Table of Contents
Executive Summary ............................................................................................................ 2
Introduction ......................................................................................................................... 3
Problem Statement .......................................................................................................... 3
Stakeholders .................................................................................................................... 3
Goals ............................................................................................................................... 4
Site Description ................................................................................................................... 5
Methods............................................................................................................................... 7
Research .............................................................................................................................. 8
Habitat Destruction, Alteration, and Fragmentation ....................................................... 8
Amphibian Movement Patterns and the Effects of Roads ............................................ 10
Global Amphibian Decline ........................................................................................... 20
Anthropogenic Causes of Amphibian Population Decline ........................................... 21
Consequences of Amphibian Loss ................................................................................ 25
Amphibians and Culverts .............................................................................................. 25
Culvert Replacement/Upgrade Costs ............................................................................ 27
Case Studies: Management Strategies ......................................................................... 29
Site Assessment Metric ................................................................................................. 32
Alternatives Table ............................................................................................................. 34
Alternatives Analysis and Discussion ............................................................................... 35
Recommendations ............................................................................................................. 38
Current Actions ............................................................................................................. 38
Further Research Needs ................................................................................................ 41
References ......................................................................................................................... 46
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Reducing Amphibian Mortality on Vermont Roadways
Prepared by students of NR 206 - University of Vermont
Executive Summary
Purpose of project
Talk about agency
Talk about why grand isle and franklin
Talk about evolution
Need for future information
This is designed to get the ball rolling until funding and knowledge catch up…
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Reducing Amphibian Mortality on Vermont Roadways
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Introduction
Problem Statement
Numerous species of amphibians found in Vermont wetlands have wide-ranging
habitat requirements, leading to movement around and between wetlands and into upland
habitats. This behavior coupled with the presence of roads through and near wetlands has
led to high levels of amphibian mortality due to vehicle encounters. No safe passage
currently exists for these delicate organisms to safely cross roads. Current actions in
Vermont are sparse and mainly consist of using fencing to prevent access to roadways.
This action is effective at reducing vehicle encounters but it will not work at any sites
with species that need to access habitat on the other side of the road. Existing
infrastructure contains thousands of road crossings such as culverts and bridges that are
currently not heavily used by amphibians while crossing roads. A management plan is
needed to utilize existing infrastructure to allow amphibians to safely cross the road while
remaining economically feasible. In order to maximize the benefits of this plan a detailed
site assessment metric is necessary.
Stakeholders

Vermont Agency of Natural Resources (VTRANS):
The reason that
amphibian road crossings may indeed become a reality in Vermont is due
to the commitment of the staff of the Vermont Agency of Transportation
(VTrans) Environmental Section. Currently, they are involved in several
projects, such as a kestrel nest box program, a “frog fence” to prevent frog
mortality on a busy state highway, mapping vegetation communities along
I-89 in an attempt to reconfigure mowing schedules to least impact
wildlife, as well as researching methods to implement more wildlife
crossings on state highways and to reduce impacts of storm water
discharges on water quality. It is their goal to make VTrans a proactive,
environmentally conscious transportation agency that will become a model
for other state transportation agencies.
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
Biologists and ecologists: This problem is of special concern to scientists
due to the numerous factors leading to widespread amphibian decline.
These species are already very stressed by habitat loss, pollution, UV
radiation, and numerous other challenges. Reptiles and amphibians are an
important link in wetland food webs.

Recreational people and sightseers: Many people relate the gentle
chirping of spring peepers or the rough calls of bullfrogs to the feeling of
being with nature. Catching frogs is a favorite activity for small children
and some adults. Cyclists have complained about high numbers of frog
road kill in the past as both disgusting and a potential safety hazard.

Motorists: Hopefully few people feel good about running over snakes,
turtles, or frogs. There is also a potential for accidents to occur while
swerving to avoid these animals.

The general public: The general public is the most important stakeholder
due to the potential need of taxpayer funding for any construction projects
related to addressing this problem. The general public may have cause for
concern over mosquitoes and mosquito-borne diseases such as West-Nile
due to the heavy feeding of amphibians on larval and adult mosquitoes.

Political Representatives: Political representatives have a measurable
impact on potential changes to be made. County representatives would be
an integral part of any construction activities, site assessment, and funding
arrangements.

Volunteers: A Boy Scout troop or other civilian group could be a useful
way to maintain silt fences or other impermanent structures. Civilian
groups from other parts of the country have formed bucket brigades to
move amphibians across the road.
Goals

Research causes and effects of amphibian decline on global and local
scales to emphasize the importance of reducing mortality sources when
feasible/possible
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
Develop a metric for assessing and prioritizing sites for their suitability
and need for road crossing modifications

Determine “why the frog crossed the road”: Conduct research to
determine why amphibians and reptiles move and come in contact with
roadways

Create a detailed list of short-term management actions for low-cost highreturn road crossing alternatives

Create a detailed list of long-term management actions for permanent road
crossing structures

Present recommendations for VTRANS to address vehicular mortality in
amphibian populations using crossing structures along Vermont-state
roads
Site Description
Vermont is located in the northwest corner of New England and is bordered by
Lake Champlain and New York state to the west; Quebec, Canada to the north; New
Hampshire to the east; and Massachusetts to the south. It is oriented primarily along a
north-south axis. Latitude is between 42º and 45º north, and longitude is between 70º and
73º west (Perkins Museum of Geology website). Total land area is approximately 9,250
square miles (U.S. Census Bureau website).
Vermont topography varies throughout the state, which has led to the state being
divided into six physiographic regions: the Green Mountains, the Taconic Mountains, the
Valley of Vermont, the Champlain Lowlands, the Vermont Piedmont, and the Northeast
Highlands. The Green Mountains run the entire north-south length of Vermont, down
approximately the middle of the state, and contain the highest peaks in Vermont. The
Taconic Mountains are located in southwest Vermont and are lower, rounder, and older
than the Green Mountains. The Valley of Vermont is a flat, narrow strip of land that runs
between the Green Mountains to the west and the Taconic Mountains to the east. It is
essentially an extension of the Champlain Lowlands, which is the area including Lake
Champlain and its surrounding, fertile, relatively flat basin. The Champlain lowlands are
bordered to the west by the Green Mountains, to the east by the Adirondack Mountains,
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and to the south by the Taconic Mountains. Due to the moderating effects of Lake
Champlain and the protection offered by the mountain ranges on three sides, this area
experiences the mildest climate in the state. The Vermont Piedmont runs the north-south
length of the state to the east of the Green Mountains, comprising the foothills of the
Green Mountains and characterized by rolling hills, wide valleys, and many lakes.
Finally, the Northeast Highlands are located in the northeast corner of Vermont and are
actually an extension of the White Mountains of New Hampshire, making them quite
different from any other region in Vermont. Here, the climate is second in severity to
only the highest peaks of the Green Mountains (Johnson 1998).
Generally, the climate of Vermont is considered humid continental-cool
summer, which is characterized by average temperature of the coldest month (January) <
32º F and average temperature of the warmest month < 72º F.
In Vermont, the
temperature is influenced more by altitude in the summer, by latitude in the winter, and
varies with topography statewide. The average length of the growing season also differs
depending on topography, from approximately 90 days at higher elevations and in small,
low valleys to 150 days near Lake Champlain. Lake Champlain has a considerable
buffering effect on the climate of the Champlain Valley (Meeks 1986).
Precipitation patterns mirror those of temperature, again varying with
topography. Average annual precipitation ranges from approximately 32” to 52”. In
general, higher elevations (Green Mountains) receive more precipitation, as do the
southern part of the state and the Northeast Highlands. Vermont is also one of the
cloudiest places in North America; the amount of solar energy that falls on Vermont is
nearly the smallest amount in the United States (Meeks 1986).
Dominant vegetation can be approximated into four primary zones. Northern
hardwoods (birch, beech, and maple) dominate below 2,000 feet, except in Northeast
Vermont. The central Champlain Valley is characterized by oak-hickory forest. Above
2,000 feet and in the Northeast Highlands, the primary vegetation communities consist of
spruce-fir. Finally, on the few peaks close to 4,000 feet, there are scattered spots of
alpine vegetation. In many of the lower elevations, such as in Franklin and Addison
Counties, dairy farms still comprise a large portion of the landscape, so these areas may
be less forested than other locations in the state (Meeks 1986).
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Vermont remains one of the most rural states in the nation, with an estimated
2001 population estimate of 613,090 people. In 2000, the average number of persons per
square mile was 65.8. Population is most dense in the Greater Burlington/Chittenden
County area, and also in the Rutland, Brattleboro, and Montpelier areas (U.S. Census
Bureau website). The 9, 250 square mile land area is traversed by a total of
approximately 15,009 miles of roads (14,305 miles of state public roads and 704 miles of
the National Highway System). In 2002, the grand total of urban and rural annual vehicle
miles of travel was 9,573.8 (VTrans website). Although it is difficult to summarize
traffic statistics, for there is too much variance between different roadways, a
generalization that may be made is that traffic decreases in intensity from Interstate
highways; down through Class I, II, III, and IV state highways; to town highways.
However, this is only a generalization, for town roads in more urbanized locations may
experience greater traffic intensity than state highways in more rural locations.
Historical Context
Methods

Research: We conducted an extensive literature review to determine the context,
extent, and factors related to amphibian mortality with roads and other causes.
Through email we communicated with people in Transportation Industry such as
Nelson Hoffman, Chris Slesar, and Chad Allen from VTRANS. Information was
also gathered via email with people in Construction Agencies such as Robert Flint
of the Florida Department of Transportation to determine costs of various efforts.
Email with biologists such as Scott Jackson from University of Massachusetts
was used to gather information on amphibian requirements for culverts.

Site Assessment: We designed a site assessment metric to prioritize sites based
on several parameters. GIS data layers containing these parameters were
downloaded Vermont Center for Geographic Information (VCGI); we utilized all
of the applicable data currently available in digital format for Grand Isle and
Franklin Counties. The metric was developed to include all culverts found within
400 meters of wetlands. This distance was chosen due to it being the approximate
maximum distance traveled by amphibians that migrate to and from wetland
habitats. Within these culverts we then prioritized sites based on traffic volume,
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viable upland habitat, and proximity to ideal amphibian habitat (wetlands). A
traffic volume of 6000 vehicles per day was selected to represent an estimated
mortality rate of >90% for amphibians crossing the road (Hels and Buchwald
2001). We then narrowed the ranges on the existing parameters to identify high
priority sites. The high priority sites were chosen based on the presence of
wetland habitat within 100 meters of a culvert (this includes the maximum
distance traveled between habitats for almost all Vermont amphibians), and a road
with a traffic volume > 6000 vehicles per day. A detailed GIS map of all highpriority sites was created including all data relevant to the metric.

Recommendations: The recommendations were compiled through analysis and
interpretation of the findings and from the results of the metric. Based on the
parameters needed for a detailed statewide site assessment metric we also
compiled a list of missing information.
Research
The following section of this report will include all of our research findings
utilized in creating recommendations for future management actions. An extensive
literature review was conducted to find both the factors and causes behind the problem as
well as potential management alternatives. Vehicle encounters are a significant source of
mortality for certain amphibian species due to movement patters and the increasing
presence of roads and vehicles near and through amphibian habitat. The need to reduce
this source of mortality is greatly strengthened by global population declines evident in
amphibian populations across the planet. These population declines are thought to be the
result of anthropogenic degradation of the global environment. This section of the report
will also present the research findings that formed the basis for our management
recommendations for future actions of the Vermont Agency of Transportation.
Habitat Destruction, Alteration, and Fragmentation
Most amphibians require both terrestrial and aquatic habitats to complete their life
cycles, which makes them even more vulnerable to habitat loss, alteration, and
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fragmentation than most other wildlife species. Loss of either habitat may have negative
impacts on amphibian populations, yet both have been greatly modified by anthropogenic
disturbances.
Some of the major land-use practices affecting amphibians include
agriculture, silviculture, industry, and urban development. These practices often lead to
the filling and draining of aquatic breeding habitat (especially wetlands and vernal pools),
the removal of trees and other vegetation in the terrestrial uplands used by adults for
feeding and refuge, and the alteration of the hydrodynamics associated with stream and
river ecosystems (Semlitsch 2003a).
Habitat destruction and habitat alteration are two distinct processes, but both have
detrimental effects on amphibian populations.
Additionally, they both contribute to
habitat fragmentation, out of which arises a host of additional problems.
Habitat
destruction is the complete, and often permanent, loss of an ecosystem and its former
biological function.
This occurs when wetlands are drained or filled; forests are
converted to parking lots, housing developments, agricultural fields, etc.; or when an
ecosystem becomes so chemically contaminated that it is uninhabitable. On the other
hand, habitat alteration occurs when an ecosystem function is changed, although not
completely or permanently. An example of habitat alteration is when trees are cut in a
forest as part of a forestry operation. Removal of the canopy will have an effect on the
microhabitat and microclimate of the forest, perhaps reducing or eliminating amphibians,
but the trees will grow back and suitable habitat will once again exist. The effects of
habitat destruction and alteration become most pronounced when they occur on a
sufficient scale that habitat fragmentation occurs (Dodd and Smith 2003).
As many amphibian populations exhibit metapopulation structure, fragmentation
of both aquatic and terrestrial habitats may lead to numerous issues. As the number of
suitable breeding sites decreases, the total number of individuals available to recolonize
extirpated populations or form new populations is diminished. This may lead to a
reduction in the number of source populations as well. The loss of aquatic habitat may
also lead to isolation of populations and the subsequent loss of genetic diversity, as they
may be too far apart to allow successful dispersal. Even more important than aquatic
breeding sites may be intact terrestrial habitat, because this provides movement corridors
that connect local populations. Because amphibians are prone to desiccation, they require
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moist microclimates provided by intact canopy cover, coarse woody debris, and leaf litter
to successfully migrate between habitats. Barriers introduced by fragmentation, such as
housing developments, roads, and agricultural fields, may restrict movement (Semlitsch
2003b).
The immediate effects of fragmentation on amphibian populations include the loss
of the most vulnerable individuals, populations, and species. As the landscape becomes
increasingly fragmented, the natural linkages between habitat patches are lost and barriers
to movement are introduced. At this point, they may become isolated from habitats
required to complete their life cycles, such as if aquatic breeding sites are cut off from
terrestrial sites.
There may be an increased risk of predation as edge effects are
introduced and cover is reduced. Fragmentation may remain a filter to movement or may
become an impenetrable barrier (Dodd and Smith 2003).
Long-term effects of fragmentation include the loss of genetic variability,
decreased survivorship, isolation, increased edge effects, and greater susceptibility to
stochastic events. Small, isolated populations confined to the tiny pieces of remaining
habitat become susceptible to the accumulation of mutations and the loss of adaptive
potential. Edge effects become more pronounced and may alter the physical structure
and microclimate of the habitat. There is often the loss of migratory routes and dispersal
corridors, compounding the problems of isolation. These long-term pressures on the
populations, combined with loss of individuals to direct mortality, can become too much
for the populations to overcome. They become more vulnerable to extirpation, and
possibly extinction, due to random stochastic events, such as disease, drought, etc. (Dodd
and Smith 2003).
Amphibian Movement Patterns and the Effects of Roads
Amphibians are frequently characterized by complex life histories, often requiring
different habitats at various life stages in order to complete their life cycles. Contrary to
popular belief, most amphibians are not entirely aquatic; in fact, some species are
completely terrestrial, and other species may require both terrestrial and aquatic habitats.
These different habitats may be widely spatially distributed, leading to the development
of metapopulation structure and dynamics.
This distribution also drives movement
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patterns in amphibians, particularly those with the biphasic life cycle, which may require
migrations between foraging, breeding, and overwintering sites.
These species are
therefore quite vulnerable to the effects of habitat fragmentation, and specifically to
mortality on roadways that bisect their home ranges (Dodd and Smith 2003).

Life History
Entirely aquatic amphibians include the salamander species hellbender
(Crytobranchus alleganiensis) and mudpuppy (Necturus maculosus), but relatively few
amphibians overall are confined to water throughout their lives. The movements of this
group are largely limited to spatial and temporal distributions within the water column
and to habitat structures within the water body. Being confined to water, they are the
group least likely to be impacted by direct mortality upon roadways, as they will not be
crossing the road and getting hit by a vehicle. The effects of roads on entirely aquatic
amphibians is probably limited to habitat destruction through road construction, impacts
from road salt and other chemicals, and other indirect impacts related to roadways (Dodd
and Smith 2003).
Other amphibians, such as the eastern red-backed salamander (Plethodon
cinereus), have entirely terrestrial life histories. These amphibians are characterized by
direct development; eggs are deposited on land and hatch into miniature adults, or they
give birth to live young (Dodd and Smith 2003). As is true for any amphibian species,
they are prone to desiccation and therefore require a humid environment, such as is
provided by the moist microclimates under deciduous forest leaf-litter and coarse woody
debris (Pough et al. 1987; deMaynadier and Hunter 1998). They may also inhabit
subterranean or arboreal habitats, and may move between subsurface, surface, and
arboreal habitats depending on season, life stage, and/or reproductive needs (Dodd and
Smith 2003). Although they may be driven to cross roads periodically, this is probably
restricted mostly to juvenile dispersal or other density-dependent causes, as roads have
been found to be the most important factor hindering amphibian movement. In fact, a
study by Gibbs (1998), in which the red-backed salamander was one of the species of
interest, demonstrated that forest-road edges are substantially less permeable than forestopen land edges and even forest-residential edges. This indicates that entirely terrestrial
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amphibians probably are not inclined to leave the forest to cross a road unless some
underlying factor necessitates it for survival.
Groups that may be forced to cross roads more frequently therefore, are the
amphibians exhibiting a biphasic life cycle, in which primarily terrestrial adults must
move to a water body to breed and deposit eggs that eventually hatch into aquatic larvae
(tadpoles). These species may be vulnerable to roadway mortality repeatedly throughout
their lives if their habitat has been fragmented by a road network.
For example,
terrestrial adults may have to cross a road to access an aquatic breeding site, and then
cross back again to return to terrestrial foraging habitat. Some species may need to cross
again to find overwintering habitat (Hels and Buchwald 2001). Upon completion of
metamorphosis, dispersing juveniles may be forced to mass migrate across roadways in
pursuit of suitable habitat. The juveniles may disperse hundreds to thousands of meters
from their natal pools, increasing the odds that they will encounter a road at some point
(Dodd and Smith 2003). As this is the group of amphibians most at risk for roadway
mortality, the remainder of this paper will focus primarily upon those with the biphasic
lifestyle.

Aquatic Breeding Habitat
Although the migration towards suitable aquatic breeding habitat is necessary for
reproduction, the destination water body varies between species. Some species utilize
large, permanent water bodies, while others prefer small, ephemeral (vernal) pools.
Generally, those species that breed in large, permanent water bodies produce larvae with
slower growth and larger body sizes at metamorphosis, which leads to increased fitness
as adults (Semlitsch 2003). An example is the American bullfrog (Rana catesbeiana),
whose tadpoles take 2 to 3 years to complete metamorphosis. This is in contrast to a
vernal pool specialist, such as the eastern spadefoot toad (Scaphiopus holbrookii), in
which metamorphosis occurs rapidly in a matter of days to weeks at the expense of
reduced body size (Dodd and Smith 2003). This speedy growth process is necessitated
by the temporary nature of the aquatic habitat; these larvae must develop quickly before
the pool dries out. But the key distinction of vernal pools is the lack of predatory fish and
tadpoles (such as the American bullfrog).
Larvae in permanent water bodies often
possess anti-predator defenses, while those in vernal pools do not. Therefore, a vernal
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pool’s hydroperiod must be long enough to allow the larvae to complete metamorphosis,
but short enough to preclude predatory fish and tadpoles (Semlitsch 2003).
A discussion of vernal pools is necessary when considering where to place road
crossings, for these pools should be prioritized in any road-crossing program. They may
possess a more diverse array of amphibian species than larger water bodies; the species
may also be of more threatened status (Dodd 1992 as cited in Semlitsch 2003). However,
vernal pools are often overlooked, even in wetland protection regulations (Preisser et al.
2000). This is an unfortunate oversight, for considering the irreplaceable function that
they provide as breeding habitat for so many amphibian species, they should be of
primary concern. For example: 14 species of frogs were found breeding in temporary
ponds within upland areas in north-central Florida (Moler and Franz as cited in Dodd and
Cade 1998), 20 amphibian species were discovered in a temporary pond on the coastal
plain of Georgia (Cash 1994 as cited in Dodd and Cade 1998), 15 amphibian species
were noted in a temporary pond in north-central Florida (Dodd 1992 as cited in Dodd and
Cade 1998), and 16 species of amphibians were documented in temporary ponds in
northern Florida flatwoods (O’Neill 1995 as cited in Dodd and Cade 1998). In New
England, vernal pool obligates include the wood frog (Rana sylvatica), eastern spadefoot
toad, spotted salamander (Ambystoma maculatum), marbled salamander (Ambystoma
opacum), and Jefferson salamander (Ambystoma jeffersonianum) (Preisser et al. 2000).

Metapopulation Dynamics
The wide spatial distribution of suitable terrestrial and aquatic habitats for
biphasic amphibians, especially the vernal pool specialists, often leads to the
development of metapopulation structure (Dodd and Smith 2003).
“A metapopulation is a set of local populations…
connected by processes of migration, gene flow, extinction,
and colonization. Two primary factors control amphibian
metapopulation dynamics: 1) the number or density of
individuals dispersing among ponds, and 2) the density and
distribution of wetlands in the landscape that determine
dispersal distances and the probability of successfully
reaching ponds” (Semlitsch 2003).
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Taking into account the factors noted by Semlitsch, loss of wetlands, and particularly
vernal pools, increases the distances between ponds and leads to the isolation of
populations.
This is particularly true for amphibians, as they cannot migrate long
distances due to the physiological limitations of desiccation. This can lead to loss of gene
flow or extirpation of local populations if the remaining wetlands are too far apart to
allow for recolonization (Semlitsch 2003).

General Effects of Roads on Amphibian Populations
One can extend this reasoning to include the effects of roadways on
metapopulations. Roadways may fragment habitat, making it more difficult to migrate to
breeding sites. Also, high mortality incurred upon roadway crossing could serve to
decimate an already stressed population. Vos and Chardon (1998) discovered that road
density has a negative effect on the occupation probability of a pond by moor frogs (Rana
arvalis). In areas with high road densities, occupation probability was reduced to 55 %.
In the part of the study adjacent to a highway, occupation probability was lowered to less
than 30 %. They point out that although the size and availability of breeding habitat is
generally thought to be the limiting factor determining population size in amphibians,
there are now indications that the distribution of suitable terrestrial habitat is becoming
more critical due to high mortality in the terrestrial phase.
This high mortality is being attributed more frequently to road kill as more roads
are built and traffic densities continue to increase. Aquatic breeding amphibians are most
vulnerable to roadway mortality due to their movement patterns, population structures,
and preferred habitats (Hels and Buchwald 2001). Amphibians are small-bodied (which
makes them less visible to drivers) (Semlitsch 2003), slow-moving, and non-cognizant of
the dangers posed by vehicles (Ashley and Robinson 1996). Generally, two factors
interact to determine where, when, and how severe roadway mortality of amphibians
occurs: the movement patterns of the species and the intensity of the traffic.

Movement Patterns
Amphibians most often encounter roads during seasonal migrations between
breeding sites, summer habitat, and hibernation sites, or during dispersal to new habitat
patches (Ashley and Robinson 1996; Vos and Chardon 1998). Ashley and Robinson
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(1996), in a study conducted along a causeway on Lake Erie, observed seasonal highs in
spring and autumn, consistent with life history patterns of reproduction and dispersal.
Depending on the species, unimodal (leopard frog) and bimodal (bullfrog) patterns of
road crossing were detected between April and October, again consistent with the life
history pattern of the species. Amphibian mortality was significantly associated with the
adjacent roadside habitat and vegetation communities preferred by various species. This
indicates that some species were attempting to cross to desirable habitat on the other side
of the causeway. The amphibians crossed mostly at night when traffic flow was light,
which may have reduced the overall mortality (Ashley and Robinson 1996). Movement
patterns may also be influenced by environmental factors, such as temperature and
moisture (Sinsch 1988; Bayliss 1995; Bartlet 2000; as cited in Muths 2000).

Roadway Mortality
The Ashley and Robinson (1996) study along a Lake Erie causeway documented
that short-lived species, which produce many young and are among the more common
and abundant amphibian species, constituted the largest numbers of road kill: northern
leopard frog (Rana pipiens), American bullfrog, green frog (Rana clamitans), and
American toad (Bufo americanus americanus). It has been noted that a species often
found killed along a road may simply reflect the presence of a large and thriving
population (Huijser and Bergers 1997; Mallick et al. 1998; both as cited in Hels and
Buchwald 2001).
Hels and Buchwald (2001) describe three factors they believe affect a species
vulnerability to road mortality: 1) velocity of the species, 2) diurnal movement pattern of
the species, and 3) diurnal movement pattern of vehicles. In their study, activity patterns
of amphibians were concentrated at night, when traffic flows were lowest, yet they still
report annual mortality of 25 % of the reproductively active adult population of spadefoot
toad (Pelobates fuscus) and 21 % of the combined reproductively active populations of
the common frog (Rana temporaria) and moor frog.
The probability of being killed increases with increasing traffic intensity (e.g.,
34% - 61% probability of being killed crossing a road with 3,207 cars per day, increasing
to 89% - 98% on a busy highway). Survival increases exponentially with velocity of the
amphibian, and decreases exponentially with increasing traffic intensity. Up to a traffic
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intensity of 625 vehicles per hour (15,000 vehicles per day), the velocity of the
amphibian has a large influence on its probability of being killed. Above this traffic
intensity, the probability of being killed is very close to 100% for all species regardless of
velocity (Hels and Buchwald 2001).
Hels and Buchwald (2001) additionally note several other interesting
observations. For example, the angle of crossing also affects probability of being killed.
Survival is greater with perpendicular crossing, with survival steadily decreasing as the
crossing angle deviates from perpendicular. Unlike most animals, amphibians, due to
their small body size, are killed mostly through direct hits by a vehicle’s wheel and may
remain unharmed if they stay still under a passing vehicle, although some larger vehicles
may kill through wind speed alone. Finally, they also note that estimates of amphibian
road kill are often underestimated, as small body sizes may mean they go undetected,
repeatedly being run over may obliterate the corpse, or they may be eaten by scavengers.

Roadway Mortality Impact
But how much of an impact does road mortality actually have on amphibian
populations? Fahrig et al (1995) found that total number of dead and live frogs per
kilometer (km) decreased with increasing traffic intensity. The proportion of dead frogs
and toads increased with increasing traffic intensity, and the density of live frogs and
toads decreased with increasing traffic intensity. Collectively, these results indicate that
traffic mortality has a significant negative effect on local density of amphibians.
At a
rate of 24 – 40 vehicles per hour, Kuhn (1987, as cited in Clevenger et al. 2001) found
that 50 % of a cohort of migrating common toads (Bufo bufo) was killed. A study by van
Gelder (1973) on common toad breeding migration estimated that 60 cars per hour would
kill 90 % of the adult toads. In yet another study, Heine (1987, as cited in Clevenger et
al. 2001) predicted that at 26 vehicles per hour, the estimated survival rate of the common
toad is zero. Ehmann and Cogger (1985, as cited in Fahrig et al. 1995) conservatively
estimated that 5,480,000 reptiles and frogs are killed annually in Australia. Ashley and
Robinson (1996) documented 27,846 road-killed young-of-the-year leopard frogs, while
total amphibian road mortality averaged 11.65 amphibians per km per day between the
months of April and October. Clearly, road mortality may have long-term impacts on
amphibian populations (Semlitsch 2003).
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Exactly how much of an impact road mortality will have depends on the species.
Some populations may be depressed by road mortality while others may experience little
impact (Ashley and Robinson 1996). It mostly depends on whether road mortality is
additive or compensatory for a given population.
In general, for adults, density-
independent mortality factors are more important, while for larvae both densitydependent and density-independent factors matter (Duellman and Trueb 1994 and
references therein, as cited in Hels and Buchwald 2001). If a population is mainly
regulated by density-independent factors, then road mortality would be an additive effect,
and the impact to the population would be greater. If a population is regulated more by
density-dependent factors, then road mortality would be compensatory, and the overall
impact on the population would be much smaller.
However, traffic intensity may
eventually increase to the point where it has an additive effect on an otherwise densitydependent population (Hels and Buchwald 2001). For threatened species, road mortality
often does have an additive effect that is detrimental to populations and metapopulations
(Semlitsch 2003).

Management Considerations: Predicting Crossing Locations
An important management consideration is how to best predict where amphibian
roadway crossings are likely to occur, so that measures may be implemented to reduce
roadway mortality, especially for species experiencing additive effects. As mentioned
previously, those species most likely to be crossing a road are those with the biphasic
lifestyle. Therefore, two habitat requirements must be within migratory proximity of a
road: terrestrial (for most species, preferably deciduous forest) and aquatic.
The
remaining questions then concern the distance an amphibian will be likely to travel to
access a given habitat type and any evident patterns to their movement directions and
pathways.
The answers to these questions vary quite widely based on species, although a
good rule of thumb would seem to be a movement distance estimate of several hundred
meters. A review of the literature offered the following wide-ranging figures, a summary
of which appears in Table One. Semlitsch (2003) states that amphibians usually live
within a few hundred meters (m) of their natal aquatic habitat, although some do disperse
to new sites. Vernal pool specialists often breed in a single pool throughout their
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reproductive lives and live in the surrounding uplands, dispersing an average of 125 m
into the uplands after breeding (Semlitsch 1998, as cited in Preisser et al. 2000). Juvenile
salamanders may disperse up to 670 m and juvenile frogs up to 1 km from their natal
pool (J. Victoria, personal communication; Berven and Grudzien 1990, both as cited in
Preisser et al. 2000).
The mean distance traveled from breeding ponds for boreal toads
(Bufo boreas) is 721.46 m (females) and 218.15 m (males); 92 % of all movements are
within 700 m of the breeding site (Muths 2003). Spadefoot toads move a maximum of
1200 m between their hibernation sites and their breeding ponds (Nöllert 1990 in Hels
and Buchwald 2001). Moor frogs migrate a maximum distance of 350 m and common
frogs a maximum distance of 600 m (Haapanen 1970 in Hels and Buchwald 2001).
Striped newts (Notophthalmus perstriatus) will travel up to 709 m, while eastern narrowmouthed toads (Gastrophryne carolinensis) will travel up to 914 m (Dodd 1996, in Dodd
and Cade 1998). The average of all the above figures is 628 m. This indicates that
amphibians will travel considerable distances for their small sizes to reach suitable
breeding and foraging habitats.
These numbers also indicate that any road within
approximately 100 m to 1,000 m of a wetland could potentially become the site of an
amphibian roadway crossing.
Movement directions and patterns also vary considerably between species,
making the identification of corridors difficult, if even possible.
Some species are
reported to move in specific directions when entering or leaving a breeding site, and it
has been suggested that some species follow migratory corridors (Stenhouse 1985;
Verrell 1987; both as cited in Dodd and Cade 1998). For example, the mole salamander
(Ambystoma talpoideum) travels to and from breeding sites in a nonrandom manner
(Semlitsch 1981, as cited in Muths 2000). Certain toads may also move in linear patterns
away from breeding sites (Bartlet 2000, as cited in Muths 2000). Shoop (1968, as cited
in Dodd and Cade 1998) detected a travel corridor approximately 30 m wide for the
spotted salamander in Massachusetts.
Other studies have found less specificity.
Stenhouse (1985, as cited in Dodd and Cade 1998) noted that individual spotted
salamanders tend to enter and exit ponds at the same location each year, although no
specific pathway is followed among a group. Dodd and Cade (1998) found that striped
newts and eastern narrow-mouthed toads favor certain directions of movement over
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others even though no specific corridor is followed, indicating that they probably move
directly to the breeding pond from their terrestrial habitat. It does appear from some of
the studies that amphibians may follow some kind of general pathway or direction during
breeding migrations, making it likely that an under-road passageway in association with
appropriate funneling techniques could prove successful in channeling the amphibians
away from death on the roadway.
Table X. Summary of distances traveled by amphibians between habitat types.
Species
Distance Traveled Between Aquatic and
Terrestrial Habitats (meters)
Amphibians, general
400
Vernal pool specialists
125
Juvenile salamanders
670
Juvenile frogs
1000
Boreal toad, female
721
Boreal toad, male
218
Spadefoot toad
1200
Moor frog
350
Common frog
600
Striped newt
709
Eastern narrow-mouthed toad
914
Average distance traveled, all species
628
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Global Amphibian Decline
A literature review of global amphibian declines was used to strengthen the need
for reducing amphibian mortality on Vermont roadways. Globally, amphibian
populations are in dire conditions due to anthropogenic impacts on the environment.
Many of the identified factors behind these declines are global problems that have no
attainable short-term solution. The combination of these mechanisms is actually enough
to lead scientists to worry about the future of amphibians as a whole. Because of this, it
is critically important to reduce sources of amphibian mortality wherever it is feasible.
The following section of this report will describe some of the sources of global
population decline

Global Population Trends
A large-scale study of global amphibian population trends was compiled which
strongly suggested population decline is occurring at a global scale (Houlahan et al 2000).
The study consisted of 936 data sets from publications, reports, and unpublished data
from 37 countries and included 157 species. This study found that a rapid global
amphibian decline from 1960-1966 was followed by a less intensive decline from 19661997. The decline rates were approximately 15% annually and 2% annually respectively
with a total of 61 documented extinctions (Houlahan et al 2000). A majority of the
historic declines were observed in Europe, but more recent rapid declines have occurred
in Costa Rica, Panama, and Australia. Until recently, most scientists believed these
declines were simply cyclical downturns in natural population dynamics. However, new
evidence indicates that these declines suggest a more catastrophic cycle (Dalton 2000).
Many of the recent population declines are of special concern due to the fact that they
occurred in protected areas such as reserves and parks with no clear causative agent
(Halliday 1998).
Several well-documented localized population declines have been observed in
relatively undisturbed sites. These declines are strong evidence for some type of global
factor that is likely an indirect anthropogenic effect (Halliday 1998). A majority of the
species-specific declines have occurred in isolated high-altitude ecosystems (Houlahan et
al 2001). There are countless examples of species-specific declines that serve to illustrate
the global connection between local declines. The Golden Toad (Bufo periglenes) was
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discovered in a Costa Rican Cloud Forest and went from fairly common with an
estimated population of 1,000 down to a single toad within a few years. The gastric
brooding frog (Rheobatrachus silius), only discovered in 1973, was found in relative
abundance until its rapid decline to extinction in 1981 (Phillips 1990).
Anthropogenic Causes of Amphibian Population Decline
A single clear causative agent for global amphibian decline has yet to be
identified, but numerous anthropogenic influences have been shown to negatively affect
amphibian populations. Mechanisms range from direct anthropogenic impacts such as
habitat destruction, to more indirect impacts such as pesticide interactions increasing
susceptibility to parasites and fungal infections.

Global Climate Change
Global climate change has been linked to two major vectors of local population
declines. Localized warming has produced niche overlapping and increased interactions
between species that historically had been isolated temporally and spatially (Walther et al
2002). Climatic warming in Britain has led to a source of population decline from a
previously insignificant interaction between populations of newts and frogs. Both species
share breeding habitats in shallow lakes and wetlands, but share different temporal
breeding niches. Warmer winters have created variable responses within the two
populations. Historically, salamanders have entered the breeding areas well after the frog
eggs have already hatched, but due to warming they are entering earlier. The frogs have
not significantly changed their breeding timing and are now suffering egg mortality from
a new source of predation (Walther et al 2002).
Climate change has also created strong warming in the air-water temperature
averages in the tropical regions of the Pacific Ocean leading to increased occurrence of
large-scale climatic oscillation cycles. These cycles drastically affect local climate in
many areas and are responsible for the recent widespread devastation observed in
numerous ecosystems from coral reefs to cloud forests (Pounds 2001). Climate change
has been implicated as an indirect cause for numerous disease outbreaks responsible for
amphibian population declines globally (Pounds 2001).
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
Fungal Pathogen Outbreaks
Global climate change has also been linked through a very complex system to
amphibian mortality through fungal infections. Numerous studies have found that certain
amphibian populations are being exposed to increased levels of UV-B radiation, resulting
in increased rates of fungal infections (Kiesecher et al 2001 and Pounds 2001).
Amphibians that breed in shallow montane lakes have been most impacted by UV-B
related mortality. Western Toads (Bufo boreas) are the most studied montane species for
this mechanism of population decline. Studies have found that their string of eggs
develop normally for a few days and then turn cloudy and white experiencing drastic
mortality from a lethal fungus infection (Pounds 2001). The fungal strain Saprolegnia
ferax has been documented as the primary cause of these population declines found in the
Northwestern United States (Kiesecher et al 2001). Most of these populations have
rapidly decreased since the 1980’s and numerous montane populations are now extinct
(Kiesecher et al 2001).
The mechanism for the
Saprolegnia ferax infection is an
example of widespread environmental
problems working together
synergistically. Previous studies had
linked fungal mortality to stratospheric
ozone depletion, but new research has
shown that climate is the primary
factor (Pounds 2001). The climatic
Figure 1: Relationship between water column depth and
hatchling survivorship (Kiesecher et al 2001)
oscillations mentioned earlier in this
report are directly correlated with
snowfall in the Cascades and therefore annual lake levels (Pounds 2001). Fungal
infections have been linked to decreased water levels, which increases UV-B exposure in
oviposition sites utilized by the Western Toad as shown in Figure 1 (Kiesecher et al
2001). This mechanism has been observed in the Western Toad and other montane
species that lay their eggs in shallow water areas. Water column depth is an efficient
filter of UV-B radiation, with eggs laid in 50 cm of water receiving half of the UV-B as
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eggs in 10cm of water (Pounds 2001). The direct mechanism for fungal infection is not
yet know but laboratory manipulation has shown in 33% increase in infection rates for
Western Toad eggs exposed to UV-B. In natural lakes, mortality rates of 80% are
common in shallow sites (20cm) while only 12% in water deeper than 50cm (Pounds
2001). Increased UV-B radiation from either stratospheric ozone depletion, or waterdraw down may also harm any other shallow water breeders as well(Pounds 2001).
Amphibian populations in Central America and the Australian Highlands are
experiencing population declines from fungal infections that appear to be from a different
mechanism. Tilarian rain frogs (Eleutherodactylus angelicus) in Costa Rica have
experienced fungal infections very similar to Western Toads, but the rain frogs lay their
eggs in shade, ruling out UV-B exposure as a causative agent (Pounds 2001). Amphibian
declines observed in Australia and Central America were caused by a chytrid fungus,
which affects cutaneous respiration. Concurrent declines in reptile populations, which
are not susceptible to this type of infection, suggest that a different mechanism must be
present (Pounds 2001). This type of chytrid fungus had not been previously documented.
The fact that it turned up on opposite sides of the world leads scientists to believe that it
is an opportunistic fungus which appeared due to compromised immune system ability,
increasing the susceptibility of amphibians to infection (Halliday 1998). Numerous other
pathogens have recently increased in abundance suggesting that environmental factors are
leading to decreased immune system function (Halliday 1998).

Herbicides
A more direct anthropogenic cause of amphibian mortality has been shown
through numerous studies relating the popular herbicide Atrazine to endocrine disruption
in frogs. Atrazine is the most commonly used herbicide in the United States, with
approximately 27,000 tons applied annually. It is also used in over 80 countries, making
Atrazine one of the most important herbicides globally (Dalton 2002). Atrazine contains
endocrine disruptors that have been linked to disruptions of sexual development in frogs
(Dalton 2002). This source of amphibian mortality was first described in the 1980’s
when researchers observed increases in frog mortality and deformities (Netting 2000).
Studies have found that levels as low as 0.1ppb cause male tadpoles to develop ovaries in
addition to testes. Levels greater that 1 ppb lead to the deformation of larynges, organs
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that are used to call for mates. Levels higher than 25 ppb are shown to cause drastic
drops in testosterone levels, which have been observed in wild leopard frogs in numerous
sites with high levels of Atrazine. Different from most lab studies of toxicity, these
numbers are ecologically relevant because American waters routinely have levels above
50ppb and in some extreme cases, concentrations can be measured in parts per million
(Dalton 2002).

Species Introduction
Species introduction is yet another anthropogenic influence that is leading to
amphibian population decline. The introduction of predatory fish to water bodies has led
to an indirect source of stress and mortality in tadpoles. When in the presence of
predatory fish, tadpoles take cover on the lake bottom and remain relatively motionless.
This behavior reduces fish predation, but it greatly increases the risk of parasite
infestation. Parasitic infestations rarely result in direct mortality, but the attacks damage
kidneys and other organs, leaving a legacy of increased susceptibility to disease as adults.
Increased stocking programs have introduced predatory fish to countless aquatic systems,
greatly increasing this mechanism of amphibian population decline (Netting 2001).
Wetland destruction can also lead to increased parasitism by concentrating tadpoles and
snails that host the parasites, in the remaining wetland patches (Netting 2001). Another
factor increasing parasitism is the potential for some pesticides to reduce vigor and
mobility of tadpoles (Netting 2001).
Bull-frog (Rana catesbeiana) and exotic fish introduction has become common
practice among permanent wetlands in the United States for aquaculture and sport-fishing
purposes, and have recently been shown to reduce populations of native anurans (Adams
1999). Bull-frogs are generalist feeders and predators that negatively impact native
amphibians through predation and competition. Many of the exotic fish commonly
introduced to aquatic systems prey on tadpoles and adult amphibians. Tadpole mortality
from fish predation can be incredibly high in some species that evolved in the absence of
predatory fish. This source of predation is very prominent in more developed areas,
where most wetlands have bullfrog or fish introduction. Some studies have found that it
is very rare to find any native amphibians in systems once bullfrogs have become
established (Adams 1999).
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Consequences of Amphibian Loss
The loss of amphibian species, through numerous mechanisms, has far-ranging
implications for ecological food-webs and ecosystem structure. Amphibian diet consists
primarily of insects, followed by other invertebrates and vertebrates. Amphibians
convert invertebrate biomass into a food source more available to higher trophic levels
(Cofrin Center for Biodiversity, 2003). Due to very small body size, amphibians are also
able to consume prey too small to be accessible to birds and mammals. An individual
Blanchard’s cricket frog consumes close to 4800 insects a year(Cofrin Center for
Biodiversity, 2003). This, coupled with very low metabolic rates, makes the conversion
of insect biomass into amphibian biomass very efficient (Pough et al, 1987). Many
amphibian species provide important ecotone interactions by foraging for insects in
upland habitats. In some Vermont forests, eastern red-backed salamander (Plethodon
cinerus) biomass is greater than birds and small mammals (Cofrin Center for
Biodiversity, 2003). The annual biomass production of red-back salamanders in these
forests can be greater than that of all birds and mammals (Pough et al, 1987). The
importance of amphibians as ecosystem and food-web components stresses the
consequences of widespread declines.
Amphibians and Culverts
Some types of amphibian crossings have been more successful than others. To
keep amphibians from crossing the road, there are a couple of options. Silt fences can be
used to deter the amphibian from crossing. They are relatively inexpensive, requiring
only wooden stakes, and canvas. However, silt fences are labor intensive and necessitate
maintenance. A community group or a Boy Scout troop could provide this upholding.
Concrete walls also deter amphibians from crossing the road. Concrete walls are more
expensive than silt fences, but require much less maintenance.
Box-shaped culverts and round culverts are options for amphibian to cross under a
road. The choices of pipes are bituminous-coated corrugated steel, High Density Polythene
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Pipe, corrugated aluminum pipe, and reinforced concrete pipe. The choice for box culverts
is concrete (LWDD, 2003).
Vermont is beginning to turn its focus towards protecting amphibians from road
mortality. Because there is less human population in Vermont, the roads have different
amounts of travel than heavily traveled Florida roads. Therefore different measures
should be taken to protect them. VTRANS could be guided by the research done at the
University of Massachusetts.
At University Of Massachusetts, Scott Jackson has led the way for the study of
amphibian culvert research. The variables affecting use are said to be size, placement,
moisture, hydrology, temperature, and noise (Jackson, 2000). It is important to consider
what amphibians prefer, when crossing under a road. “Relatively small amphibian and
reptile tunnels may be a cost effective means of mitigating highway impacts where roads
and highways are located between wetlands and upland habitats” (Jackson, 2000).
Scott Jackson recommends using box culverts over pipes. As for the size, he
suggests bigger culverts with a wider diameter. This will
be more accessible for animals meaning less mortality.
Jackson advises at least two feet by two feet squared at
the openings. Open tops that allow light will attract more
amphibians. Jackson suggests using concrete. If a pipe is
to be used, he also suggests a good standard culvert
Image of a box culvert from
http://www.acousa.com/wildlife.htm
diameter is fifteen inches (Jackson, 2000).
Gino Guimarro the senior project manager at Woodlot Alternatives, an
environmental consultant firm, states that a square bottom would have more usable
bottom area (Guimarro, 2003). He also believes culverts should be up to 36 inches
diameter to allow bigger animals such as racoons through (Ruediger, 2003).
The substrate of the culvert is important for promoting amphibian crossing.
Jackson advocates using sandy soil for the bottom of the culvert as well as providing
cover such as tree stumps. Bill Ruediger, the Ecology Program Leader for Highways at
the USDA Forest Service’s Washington Office recommends a natural bottom surface
such as rock or dirt (Ruediger, 2003).
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Culvert Showing natural substrate and wing walls to guide amphibians under the
road.http://www.fhwa.dot.gov/environment/wildlifecrossings/photo25.htm
Wing walls are used to funnel the amphibians into the tunnel. The wing walls
ought to extend at forty-five degrees to funnel the amphibians toward the culvert. The
walls should extend vertically at least eighteen inches. The vertical walls should extend
one hundred to two hundred feet outward and the tops of the walls should be parallel with
the ground surface on the side closest to the road. Jackson recommends that the crossing
structures should be placed less than one hundred feet apart (Jackson, 2000).
Comparison of different culvert types is important for Vermont so that the least
expensive measure can be used. “There is evidence that amphibian and reptile tunnels are
effective when used with two lane roads…. it is not known how effective they will be for
facilitating passage beneath highways of four or more lanes” (Langston et al in Jackson,
2000). Ruediger recommends in order of preference, cement box culverts, cement round
culverts, PVC pipe, then corrugated steel as the least preferable (Ruediger, 2003).
Culvert Replacement/Upgrade Costs
Round culverts are less expensive than box shaped culverts, so in the interest of
budget; this paper will focus on them. The four types of materials used for pipe culverts
are steel, aluminum, and concrete, and HDPE, or High Density Polythene Pipe. Table 11
shows the cost of production and the installation price for two lane roads. The table also
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shows the budget for VTRANS in 2004. $50,722,184 goes to maintenance, which is
where the culvert replacement would take place (Hoffman, 2003).
Table 1. The price of different culvert materials and installation.
Culvert Type
2 lane cost (per foot) + $750 installation
HDPE 15 inch diameter
21.04
Concrete Box Culvert 2x2 ft
350-700
Reinforced Concrete Pipe
28
Corrugated Metal Pipe
26.12
Total Budget for VTRANS 2004
Amount of VTRANS available for Culverts
$301,404,219
$50,722,184
Dave Lathrop of (??) averages culvert replacement costs between $5,000 $10,000 dollars. He states that amphibian culverts are closer to $5,000 because they are
dug at a small depth. However, the figures depend on many variables such as size and
length of culvert, traffic control, and depth of culvert (Lathrop, 2003).
Gil Newbury of (???) states that the minimum culvert size used under state
highways is 18 inches. Also culverts less than 4 feet in diameter are primarily made of
plastic. Gil adds that cost depends not only on depth, but also on the wetness of the site.
He expects a cost of between $3,000 and $5,000 (Newbury, 2003).
Chris Slesar of VTRANS states that access to a site will affect the cost. He uses
the example that if a culvert needs to be installed on a steep slope, then more labor will
increase the costs. Other variables he lists are traffic volumes and guard rail presence
(Slesar, 2003).
Chad Allen of VTRANS says that the material cost of HDPE, CMP, and RCP (reinforced concrete pipe) are $21.04/LF, $26.12/LF, and $28.00/LF correspondingly.
Therefore if a 35 to 40 foot pipe was fitted under a 2 lane road, then the difference in
material only comes out to about $150-$200. For a $5,500 job, this is fairly unimportant.
Allen also states that the District's first choice is to install HDPE. The other materials
such as CMP, are used in areas where the culvert needs to be installed deep within the
ground (Allen, 2003).
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The problems encountered are that price of the pipes depends on how much the
consumer will buy. Robert Flint of the Florida Department of Transportation explains
that the more bulk of pipe bought, the less expensive it will be. He said “ we may have a
price for a 24" pipe (Concrete Pipe) that is 8 ft. long. If the quantity needed is 1,000 ft.,
then the price is $23.00 per foot” (Flint, 2003). Also, a potential problem is the culvert’s
function in a storm event. Chad Allen, District 5 Transportation Program Manager,
recommends that the culvert equalize water between wetlands or push water away from
the road (Allen, 2003).
Case Studies: Management Strategies

Switzerland
Switzerland has a long history of research and action based on animal crossing.
Swiss scientists have developed a Geographic Information System (GIS) that shows
animal habitat and corridors where many animals travel across roads. In these places, the
Swiss have adapted numerous methods for preventing animal collisions with cars. When
the concern is only larger game like deer, they have constructed warning signs that can
detect animal movement along roadside. When an animal moves across the motion
detector the sign flashes on warning oncoming traffic that something is close to the road.
Constructing large animal overpasses is another method used by the Swiss.
Through many studies the Swiss have determined that the best overpass for animal use
would have a minimum width of 50 meters (Bank, 2002). By incorporating vegetation
and water, the overpass is like the natural environment (Figure 1). This method has
proven successful with a wide variety of users from large game to small amphibians and
insects. Overpasses are constructed with video cameras and tracking plots to measure
their effectiveness. Tracking plots are built in the crossings and have either ink pads that
dirty up the animals feet causing it to leave tracks, or fine sand pits that the animal must
cross over. When crossed the fine sand will have imprints of the animal’s feet (Sauvajot
2002).
When the target animals are small mammals or amphibians an underpass may be
used. There are many different methods for building underpasses but one that the Swiss
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have used is a one-way tunnel system. This system funnels amphibians from upland
habitats to breeding sites in the spring and fall. The only way for the animal to cross the
road is through the one-way viaduct, this lowers animal death and still allows the
amphibians to reach their breeding ground without major difficulty. One major method
the Swiss use to ensure the safety of animals at road crossing is teamwork between
transportation and environmental planners. Without teamwork and concern for the
animals not much can be accomplished (Sauvajot 2002).

Germany
Germany has gone in slightly a different direction when dealing with overpasses.
They have created their overpasses to be used by more then just animals. They have
created their overpasses to incorporate humans as well as animals. In farm areas, they
have built overpasses with tractor trails as well as pathways for walking and biking. This
method is beneficial to animals and the
local communities. These overpasses not
only connect habitat but also farmland. In
addition, Germany has focused on
underpasses that are built specifically to
prevent noise pollution. Passing cars
create noise that prevents some animals
Figure 2: Cement underpass without sound buffers
from using the tunnels. By building
tunnels deeper under the road, it cuts down on some of the noise pollution. In Figure 2,
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the underpass is built just under the road’s surface. This underpass does not sufficiently
cut down on noise. Different types of fences can also be used to cut down on the noise
near roads (Hagood, 2002).

The Netherlands
The Netherlands has used similar methods as the other countries. Overpasses are
built for all types of animals, from large mammals to small insects and many underpasses
have been built for small mammals and amphibians. In their underpasses they have built
in wood or earth shelves that are built for mammals to cross in watery culverts. In all, the
Netherlands have approximately 600 culverts, with only ten built specifically for
amphibians (Gray, 2002).

The United States
The United States has come a long way since concern over wildlife began around
roadways. Many states have begun planning and building crossings. Florida for
example, has already created many amphibian crossing areas. They have progressed
faster then most of the other states and they have an extensive system of crossing
culverts. In one two mile stretch on Route 441 in Florida, they have built a 3 1/5 foot
high concrete wall with a 6 inch lip at the top (as seen in Figure 3) that directs reptiles
and amphibians along the road to an underpass (Southall, 2000). This wall prevents
animals from climbing to the roads and it has been a success.
Figure 3: Florida roadway
Concern throughout the United States has been growing and something must soon
be done. Many planning committees have used the methods discovered and implemented
in Europe. There is no one solution, each situation is separate and can be handled
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differently. The future for animal crossings here in the United States looks promising.
As long as there is public concern, animals will be protected.
Site Assessment Metric

The Purpose of a Metric
From measuring the success and excellence of businesses, to quantifying a range
of ecological factors, metrics can be used for a multitude of useful applications. In recent
years, they have been used to assess biodiversity, degrees of environmental degradation
(Sutter 1992), population dynamics, and habitat suitability (Mitch and Gosselink 2000).
Indeed, metrics, also often referred to as indices, can be used to evaluate largely anything
that a scientist might desire to study. In the environmental field, the use of metrics has
proven to be a successful method for quantifying otherwise subjective environmental
factors.

Assessing Sites of Amphibian Mortality
The development of a metric is a somewhat arbitrary practice. However, in this
instance a metric is simply a useful by-product of a landscape/habitat assessment.
VTRANS, the state of Vermont’s transportation department, has expressed a desire to
implement a program designed to prevent amphibian mortality due to road crossings.
Each year, large quantities of amphibians are flattened by passing cars, which presents
both environmental and safety problems. VTRANS has experimented with small-scale
structures designed to prevent amphibians from crossing state highways, however, they
are interested in more permanent solutions to a problem they anticipate will otherwise be
long-term.

Inherent Limitations of Metrics
As is true with any metric, there will be flaws inherent to the final product, most
often related to incomplete, insufficient, or inaccurate data.
Please refer to the
“Recommendations for Further Research” section of this paper for information on
missing data related to our metric. In any instance, it is recommended that any necessary,
or otherwise helpful, data be obtained as soon as possible in order to facilitate the further
development of the metric. Lack of funding may preclude extensive data collection,
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although the hiring of college interns or other relatively inexpensive help could assist in
making the data collection possible.
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Alternatives Table
Decrease
Mortality
Habitat
Connectivity
No Action
Temporary Road
Closing
No Change
100% decrease
when implemented
No Change
Temporary Barriers
to Crossing
Close to 100%
No Change
Reduced by
almost 100
Percent
Slight Decrease
No Change
Decrease
Warning Signs
Add Temporary
Funneling Walls to
Culverts
Replace Existing
Culverts to be More
Suitable Towards
Amphibians
Humans Moving
Amphibians in
Buckets
Permanent Funnel
Wall Construction
Specific Culverts for
Amphibians
Wilderness
Overpass
Public Support/
Involvement
Volunteers
Needed
None
None
Costs
No
Change
Maximum
None
Low
Minimum
Maximum
Low
Minimum
Minimum
Low
Increase
No Change
Barriers will be visible
from road, but will
decrease roadkill
Slight Decrease due to
more signs
Walls will be visible
from road, but will
decrease roadkill
Minimum
Maximum
Low
Decrease
Large decrease
only when
implemented
Increase
Decrease roadkill
Minimum
Minimum
Low
No Change
Minimum
Maximum
Low
Decrease
Increase
Decrease Roadkill
May be visible from
road, will decrease
roadkill
Maximum
Minimum
High
Decrease
Increase
Decrease roadkill
Maximum
Minimum
Decrease
Increase
Personal Preference
Maximum
Minimum
Medium
Very
High
Aesthetics
Continue to see dead
amphibians on road
Need 1 sentence qualifiers in footnote for maximum, etc
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Alternatives Analysis and Discussion

No Action
This alternative suggests the Agency of Transportation to continue with the same
policies that they currently have. There would be no increase in spending or change in
policy. This alternative does not address the problem. It does nothing to prevent
amphibian mortality, raise public awareness, or raise the level of connectivity.

Closing Roads
This alternative addresses the problem and would prevent amphibian mortality,
but only a couple times a year. It does nothing to address the problem during the rest of
the year. It does nothing to increase connectivity. By closing the roads the public may
be upset but it will cause them to question why this is happening, raising overall
awareness of the topic.

Temporary Barriers to Crossing
By building temporary barriers the mortality rate will be decreased almost
completely. The barriers will prevent amphibians from getting onto the roads. They are
cheap and easy to install but will need volunteer help with installation, upkeep and
deconstruction. One problem with this alternative is connectivity. Barriers from the road
with no crossing mechanism completely decrease connectivity.

Warning Signs
Warning Signs are fairly inexpensive and they have little upkeep. They are easy
to implement and do not need much public support. This alternative does little to prevent
amphibian mortality. It does nothing to prevent amphibians from going onto roads. It
only makes a suggestion to drivers to be careful and does nothing to enforce driver safety.
This alternative does not help with connectivity.

Add Temporary Funneling Walls to Culverts
This alternative will decrease mortality because it will direct amphibians toward
the culvert entrance. It will increase the amphibian populations because less will be killed
in the roads. However, the wall could confuse the amphibians that don’t move along the
fence. This would make them likely to be predated on by birds. Habitats would be
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connected using this alternative, unless wear and tear happens to the silt fence. The
aesthetics of a silt fence would be intermediate because they are used commonly for
house construction. This alternative requires a great amount of labor. The fence must be
constructed in the late spring or early summer and taken down in the fall and could be
done by civilian groups such as boy scouts. The prices of the drift fences are minimal in
comparison with a more permanent lipped concrete wall.

Replace Existing Culverts
This alternative would decrease amphibian mortality by making the culverts more
accessible for amphibian to cross. This alternative would increase habitat connectivity
and would have the potential to increase aesthetics. The public support would be minimal
as well as the volunteers needed. In this case, existing culverts will need to be replaced
anyway. The cost would depend on what alterations needed to be done and could range
greatly.

Humans Moving Amphibians in Buckets
This alternative would require a lot of volunteer work moving amphibians across
the road. It would mean a decrease in mortality in the high migration points of the year,
but could not guarantee 100% survival and does nothing for any other times throughout
the year. It would have no affect on habitat connectivity, and would not affect aesthetics
because nothing is being changed. It would be positive because it would encourage
community interactions with each other and the environment. This alternative would cost
nothing to the state but could have an effect on the traffic, such as causing people to slow
down.

Permanent Funnel Wall Construction
This alternative would decrease mortality and would be beneficial because it
would not require much maintenance. This alternative would connect two habitats almost
seamlessly. The aesthetics of a concrete wall would be negative. In order to get the
funding for a project like this, public support would be needed. Volunteers would not be
needed for this project. The cost of this project would be high.
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
Specific Culverts for Amphibians
These culverts would nearly eliminate mortality and would maximize habitat
connectivity. Amphibian specific culverts are seamless which could have the potential to
increase aesthetics. Public support would be needed to encourage VTRANS to install this
type of culvert. No volunteers would be needed. The price of these culverts is high.

Wilderness Overpass
The potential for a wilderness overpass could nearly eliminate mortality by
naturally connecting two habitats. An overpass would be aesthetically pleasing to people
who view nature as good. Public support for this project would be needed to encourage
VTRANS funding. No volunteers would be needed. The cost would be very expensive
taking into consideration that bridges cost more than digging a culvert.
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Recommendations
The main goal of this report is to provide management recommendation for the
Vermont Agency of Transportation to address the problem of amphibian mortality on
Vermont roadways. This report has thus far presented background information on the
problem and has provided a list of possible management alternatives. Our
recommendation to the agency is not to select a single alternative, but to work within the
framework of actions utilizing adaptive management. Due to funding and public support
limitations many of the alternatives are not currently feasible. If the project is successful
public support and funding will gradually increase making further actions possible. This
section of the report will first outline our short-term management recommendations, and
then discuss the importance of public support and the information that is still needed to
finalize the metric for statewide usage. Our long-term recommendations are based on the
compilation of currently lacking datasets as well as increased funding, which will
hopefully be available in the future.
Current Actions
In order to maximize the benefits to amphibians while working within the
constraints of funding limitations, we strongly recommend that VTRANS work to
implement several of the low-cost alternatives at high-priority sites. The initial actions
should be directed at both reducing mortality while raising public awareness. We
recommend a combination of amphibian crossing signs and installation of silt-fence
funnel walls into existing culverts. We also recommend the continued usage of silt-fence
barrier walls at sites where the amphibians do not need to cross the road, similar to the
current program on Rt. 2 at Sandbar. The site assessment metric was used to identify 3
high priority sites based on proximity to wetlands and high traffic volume. These sites
would be a good starting point to test the effectiveness and feasibility of implementing
the alternatives presented in this report. If these sites are successful in both raising
awareness of the issue and in reducing amphibian mortality, then more sites should be
selected for action. By proving the effectiveness of these actions it will be possible to
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gain further public support and funding to allow the implementation of more expensive
and more permanent management alternatives.

Monitoring
One crucial aspect of implementing amphibian-crossing measures is monitoring
their effectiveness. In order for the statewide effort to gain momentum and public
support, results must be evident. Installation of amphibian crossing structures must be
proven to be both used by amphibians and to reduce roadway mortality. Currently,
VTRANS documents amphibian mortality by spray painting carcasses on the roadway so
that they are not counted again in the future. This method is fairly effective, but it does
not capture all of the mortality due to some amphibians being obliterated upon impact, or
taken off of the road by scavengers before they are counted. This method is very
inexpensive and will be an integral part of any effectiveness monitoring. One-time
counts at previously un-assessed sites can also be used to estimate the degree of mortality
rates.
Monitoring will also be crucial in determining the usage of crossing structures.
Jim Andrews recommended using bucket traps set in the ground at the mouth of culvert
on the far side of the road. Amphibians simply fall into these buckets after crossing the
road and are trapped by the steep smooth walls. The buckets must be checked several
times a night to identify, count, and release all of the organisms. This method is very
effective but there are two major concerns. Any predator lucky enough to stumble upon a
bucket full of tasty frogs is a serious threat, but the use of a raised grate can easily keep
predators out. Another concern is the amount of labor needed to maintain these traps.
Volunteers are the best option to work through the night checking the traps. Monitoring
to prove the effectiveness of crossing structures will be a integral part of gaining public
support to continue the evolution of this project in Vermont.

Public Support
An effective amphibian road-crossing program could end up being quite costly,
and if implemented by a state agency, the funds could primarily come from tax dollars.
Therefore, public support will be essential to any amphibian road-crossing plan.
However, as amphibians are not at the forefront of most wildlife activism crusades,
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public support may be more difficult to gain than it would be for more majestic wildlife
species. A comprehensive plan for gathering public support must be developed prior to
enacting any amphibian-crossing project.
Although the intent of this paper is not to develop a plan for developing public
support, several brief suggestions will be noted. A concern is that public support will be
difficult to procure, because many people do not value amphibians the way they may
value more visible and well-understood wildlife species. One way to educate the public
about these critters is to hold a series of informational public meetings across the state
when the decision is made to fund a crossing program, at least partially, with tax dollars.
Another medium that may be used to reach the public is the media, such as descriptive
articles in local newspapers or segments on local news programs.
An additional
suggestion is to appeal to fishermen, birdwatchers, and other outdoors people by
including information about amphibians’ importance at the base of the food chain, and
the implications of this for other wildlife, in fishing regulation books and at wildlife
refuges and other access areas.
One way to reach a large segment of the public in a positive manner is through
enlightened children.
Guest speakers on amphibians, along with live specimens,
incorporated into elementary school curriculums would raise the interest and awareness
of the students. The students would then, hopefully, go home and inform their families of
what they learned; that is, they would relay to the adults the importance of amphibians
and how a road crossing program can help reduce mortality. A child’s enthusiasm for a
given subject is often a more effective method for swaying an adult’s opinion than is any
public service announcement.
One of the most important aspects of public support involved with this project is
the need for volunteer efforts and ownership. Unfortunately, most of our short-term
management recommendations require a large degree of labor. The labor needs include
installing, maintaining, and removing the silt fencing every year, to checking bucket traps
used in monitoring, to carrying amphibians across to safety in a bucket brigade. We
suggest that community groups such as Boy Scout troops or Science classes be
approached to take ownership of the labor needs at the sites. As discussed earlier, public
involvement can be used to benefit both the public through education and the amphibians.
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Further Research Needs
INTRO PARAGRAPH

Culvert Data – More comprehensive culvert data would be useful to
determine replacement needs.
Specifically, it should be noted that data
pertaining to size and the date of last replacement for each culvert are not
available in digital format at this time; it will take a substantial amount of time
and effort to compile this data into a usable format. In addition, it will be
necessary to collect data regarding the average “wetness” of the culverts
contained within the study area. The amount of water that flows through a
culvert dictates whether or not an amphibian would be capable of passing
through it (Andrews 2003). Since such a database does not currently exist, it
will be necessary to develop one before the metric can be truly completed.

Endangered Species Data - It should be noted that the endangered species
database for the state of Vermont has not been updated since 1997 (VT FWS
1997); this data may need to be updated accordingly. This may be done,
specifically for amphibians, utilizing town-level documented species data for
the state. This data, developed as part of the Vermont Biodiversity Project, is
available through the Vermont Center for Geographic Information and was
most recently updated in 2000 (Buford 2000).

Known Crossing Sites – It is important to include all known sites of high
amphibian mortality (due to road crossings) in the state, and any known sites
of high amphibian movement/migration. This data will aid in determining
which areas are most in need of amphibian crossing structures. However,
such data has not been compiled as of date (Hoffman 2003) and will therefore
need to be collected and put into digital format before addition to the metric.
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
Species Distribution, Density and Diversity – Data is lacking as to exactly
where amphibian populations occur in Vermont. For this project, we could
only consider wetlands and other habitat where amphibians may be likely to
occur. It would be more helpful to know those locations where, indeed, they
do occur.

More Information On Locations of Vernal Pools - The state currently
provides access to National Wetlands Inventory (NWI) wetland location maps
for the state. However, NWI maps are developed at a 1:250,000 scale (Tuggle
and Wilen 2003), and all of the data available carries a disclaimer regarding
the inherent limitations of data developed at this scale (US FWS 2003).
Essentially, in treeless areas, wetlands ¼ of an acre and larger are accurately
depicted, in forested areas, the minimum wetland size depicted ranges
between 1 and 3 acres (CGDB 2003, WGISC 2003).
This means that
although wetlands provide an ideal habitat for most amphibians, not all
wetlands within the state will be included in the analysis of available habitat.
This is especially true for small, temporary wetlands, such as vernal pools.
We recommend the collection of data on the location of these important
habitats.

Global Populations - A lack of clear scientific understanding is the largest
hurdle in addressing the global amphibian crisis. A majority of our current
understanding is from the US, Europe, and Australia, all of which are areas of
relatively low amphibian diversity (Houlahan et al 2000). The fact that largescale declines have been observed in many isolated and relatively undisturbed
sites can be extrapolated to mean that numerous declines have and are
occurring in poorly documented sites with high diversity (Young et al 2001).
Latin America is a strong example of the lack of scientific understanding and
the implications of this issue. Latin America contains over half of the world’s
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amphibian richness, some declines have been documented, but it is estimated
that 5-10% of the species in Latin America are undocumented. Because of
this it is impossible to fully understand and quantify population declines
(Young et al 2001).

Cause of Global Decline - Current research has found numerous sources of
local population mortality, but a clear global causative agent is lacking. Due
to the sensitive nature of amphibian species it is possible that a host of
different stresses are working synergistically to harm populations globally.
Further research is needed to document all amphibian populations, particularly
those in the lesser studied areas of high diversity. Many of the studies suggest
that protecting habitat is only a beginning due to the insidious nature of some
of the threats such as UV-B radiation. The fact that many of the identified
causative agents can not be easily reversed emphasizing the importance of
identifying and remediating all other mechanisms such as Atrazine to reduce
the stresses on amphibian populations and reduce the risk of global extinctions

Long-term recommendations for VTRANS
INTRO PARAGRAPH

Larger Culverts - Our research has indicated that most amphibians found
within the state are likely to move through larger culverts, as they allow more
natural light to pass through. They are also more conducive to the long-term
maintenance of natural ground cover throughout, providing further appeal to
amphibians. Finally, it should also be noted that larger culverts are more
likely to have room to allow for both water flow and amphibian passage
(Andrews 2003).

Focus on Rare, Threatened, and Endangered Species - This is not only for
environmental purposes but political purposes as well; amphibians carry a
public stigma and thus funds will be more readily available to develop
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crossing alternatives if rare or threatened species are at the forefront of the
issue (Andrews 2003).

Focus on Areas with High Species Density and/or Diversity - It makes the
most sense, both in terms of environmental conditions and economic
conditions, to first consider sites that are surrounded by a high density and
diversity of amphibians. This idea plays into the policy of getting the “most
bang for your buck”.

Addition of Raised Structures Within Culverts with Regularly Flowing
Water - While most amphibians require a moist environment, a culvert with
consistently flowing water would not provide an ideal crossing environment.
The state should consider installing culverts with modifications that would
allow the amphibians to bypass the water flow (i.e. culverts with raised
centers, designed to provide a transport route while directing channel flow
along either side of the route).

Replacement of Culverts on an As-Needed Basis - Logically, it is most
cost-effective to replace culverts only when they need to be replaced due to
structural damage to either the culvert itself or the road above it. Therefore,
we recommend that the final culverts selected to serve as amphibian crossings
be replaced on an “as-needed” schedule (unless ecologic conditions dictate
replacement sooner), to reduce costs to the state and ultimately, to taxpayers.

Focus on Sites with Documented Road Mortality - Since there have been
documented amphibian mortality problems at these sites, it would be helpful
to both motorists and the environment to take action.

Focus on Sites with High Traffic Intensity - If necessary (if the selection
processes described above yield a high number of potential sites), traffic
volume data may be used to further prioritize sites. If this is the case, we
suggest that the above prioritizations be followed, but within each category,
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those sites with the largest amount of traffic volume be considered for action
first.

Adaptive Management - Finally, as with any project designed to address
specific environmental problems, the practice of adaptive management will
need to be implemented to garner the most successful results.
The true
outcome of a project can never be known until it has been implemented in the
real world; if problems or complications arise, it will be necessary to go back
to the original plans and alter them accordingly.

GO MORE INTO ADAPTIVE MANAGEMENT
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Contact’s List
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Relevant appendices
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