ACKNOWLEDGEMENTS
Funding and support for this project was provided by the United States Air Force,
Texas Tech University, and the United States Geological Survey-Texas Cooperative Fish
and Wildlife Research Unit. I would like to thank Dr. Phillip Zwank for providing the
opportunity for me to pursue a master’s degree and for his invariably cheerful attitude.
Tragically, Dr. Zwank passed away before completion of this project, and he is sincerely
missed by myself, as well as others who knew him. I would like to thank Dr. Clint Boal
for consenting to serve as my advisor after Dr. Zwank’s passing. His support and
guidance in seeing this project to completion is very much appreciated. I would also like
to thank the remaining members of my graduate committee, Dr. Mark Wallace and Dr.
Terry Bashore for their support and review of my thesis. I thank Dr. Warren Ballard for
aid and support, and Dr. David Wester for assistance in statistical analysis.
I am indebted to Julie and Jeff Boatright, Shawn Swearingen, Patrick Lemmons,
and Doug Knabe, for assistance in field work, and John and Tina Brunjes for frequent
guidance in logistical matters. I would also like to thank the many friends I have made in
the department for their support and friendship. I would especially like to thank my
parents for their love, patience, and financial and mental support throughout my academic
endeavors. Lastly, I would like to thank Reese Ranta for her love, patience,
psychological and medical support, positive attitude, and not least of all for
accompanying me to Lubbock to pursue a graduate degree.
ii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS........................................................................................... ii
LIST OF TABLES......................................................................................................... iv
LIST OF FIGURES....................................................................................................... vi
CHAPTER
I.
GENERAL INTRODUCTION.............................................................. 1
II.
RAPTOR ABUNDANCE IN RELATION TO
BLACK-TAILED PRAIRIE DOG COLONIES................................... 3
Introduction................................................................................ 3
Methods.....................................................................................
6
Results........................................................................................ 9
Discussion.................................................................................. 13
Literature Cited.......................................................................... 23
III.
EFFICACY OF VISUAL BARRIERS IN REDUCTION OF
BLACK-TAILED PRAIRIE DOG COLONY EXPANSION.............. 40
Introduction................................................................................ 40
Methods..................................................................................... 43
Results........................................................................................ 45
Discussion.................................................................................. 46
Literature Cited.......................................................................... 48
iii
LIST OF TABLES
2.1 Presence (denoted by an “X”) or absence of birds at Lubbock County,
Texas (LCTX) and Melrose Bombing and Gunnery Range (Range),
Roosevelt County, New Mexico, as determined by point counts in 2002......... 29
2.2 Mean number of cattle egrets detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and
non-colony plots in Lubbock County, Texas (LCTX) and at Melrose
Bombing and Gunnery Range (MBGR) in 2002............................................... 30
2.3 Mean number of turkey vultures detected at n plots (number
of surveys X number of plots) on a seasonal and annual (year) basis at
colony and non-colony plots in Lubbock County, Texas (LCTX) and
at Melrose Bombing and Gunnery Range (MBGR) in 2002............................. 31
2.4 Mean number of burrowing owls detected at n plots (number of surveys
X number of plots) on a seasonal and annual (year) basis at colony and
non-colony plots in Lubbock County, Texas (LCTX) and at Melrose
Bombing and Gunnery Range (MBGR) in 2002. All reported statistics were
calculated using a Kruskal-Wallis test............................................................... 32
2.5 Mean number of northern harriers detected at n plots (number of surveys
X number of plots) on a seasonal and annual (year) basis at colony and
non-colony plots in Lubbock County, Texas (LCTX) and at Melrose
Bombing and Gunnery Range (MBGR) in 2002............................................... 33
2.6 Mean number of Swainson’s hawks detected at n plots (number of
surveys X number of plots) on a seasonal and annual (year) basis at
colony and non-colony plots in Lubbock County, Texas (LCTX) and
at Melrose Bombing and Gunnery Range (MBGR) in 2002............................. 34
2.7 Mean number of red-tailed hawks detected at n plots (number of surveys
X number of plots) on a seasonal and annual (year) basis at colony and
non-colony plots in Lubbock County, Texas (LCTX) and at Melrose
Bombing and Gunnery Range (MBGR) in 2002............................................... 35
2.8 Mean number of ferruginous hawks detected at n plots (number of
surveys X number of plots) on a seasonal and annual (year) basis at
colony and non-colony plots in Lubbock County, Texas (LCTX) and
at Melrose Bombing and Gunnery Range (MBGR) in 2002............................. 36
iv
2.9 Mean number of American kestrels detected at n plots (number of
surveys X number of plots) on a seasonal and annual (year) basis at
colony and non-colony plots in Lubbock County, Texas (LCTX) and
at Melrose Bombing and Gunnery Range (MBGR) in 2002............................. 37
2.10 Mean number of all birds detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and
non-colony plots in Lubbock County, Texas (LCTX) and at Melrose
Bombing and Gunnery Range (MBGR) in 2002............................................... 38
2.11 Mean number of Chihuahuan ravens detected at n plots (number of
surveys X number of plots) on a seasonal and annual (year) basis at
colony and non-colony plots in Lubbock County, Texas (LCTX)
and at Melrose Bombing and Gunnery Range (MBGR) in 2002...................... 39
v
LIST OF FIGURES
2.1 Location of study sites for point counts conducted in 2002, including
Melrose Bombing and Gunnery Range in Roosevelt County, New
Mexico, and southern Lubbock County, Texas................................................. 28
3.1 Spatial arrangement of experiment addressing efficacy of visual barriers
in reduction of prairie dog colony expansion at Melrose Bombing and
Gunnery Range, Roosevelt County, New Mexico, summer 2002..................... 50
3.2 Burrows detected by survey date for each treatment of galvanized roofing,
silt fencing and control at prairie dog colonies at Melrose Bombing and
Gunnery Range, Roosevelt County, New Mexico, summer 2002..................... 51
vi
CHAPTER I
GENERAL INTRODUCTION
This project was initiated with 2 main objectives. The first objective was to
determine if the presence of active black-tailed prairie dog colonies has an impact on the
relative abundance of diurnal raptors, thus affecting the risk of bird-aircraft collisions.
The second objective was to determine if silt fencing and galvanized roofing panels were
durable and effective materials in reducing prairie dog colony expansion as visual
barriers. Research addressing the former objective was conducted at 2 sites to evaluate
species-specific patterns of relative abundance of raptors at areas occupied and
unoccupied by prairie dogs in differing landscape types. Sites included southern
Lubbock County, Texas, as well as on and within the vicinity of Melrose Bombing and
Gunnery Range (MBGR), an F-16 bombing and strafing training site in east-central New
Mexico. Research addressing the latter objective was conducted exclusively at the
Range.
Despite the fact that black-tailed prairie dogs are a candidate species, control of
this species is planned at MBGR in hopes of decreasing bird-aircraft strike hazard by
reducing raptor numbers. No previous research has compared the total number of raptors
on and off prairie dog colonies, thus prairie dog control has not been scientifically
justified as a means of raptor management. This study was implemented, in part, to
address that issue; results of this portion are included in Chapter II. Visual barriers are a
frequently used, but seldom tested non-lethal prairie dog management technique.
Efficacy of this technique was tested as part of this study; results are addressed in
1
Chapter III. Chapters II and III will be submitted for publication separately. Authors to
be included on Chapter II include Joel W. Merriman, Phillip J. Zwank, Clint W. Boal,
Terry L. Bashore, and David B. Wester. Authors to be included on Chapter III include
Joel W. Merriman, Phillip J. Zwank, Clint W. Boal, and Terry L. Bashore.
2
CHAPTER II
RAPTOR ABUNDANCE IN RELATION TO
BLACK-TAILED PRAIRIE DOG COLONIES
Introduction
Bird strike hazard is a serious economic and human safety issue that has become
increasingly problematic in recent years due to increases in air traffic and in populations
of some species of birds that pose high strike hazard (Dolbeer et al. 2000, Cleary et al.
2002, Sodhi 2002). Cleary et al. (2002) estimate that from 1990-2001, wildlife strikes
cost the United States civil aviation industry $469.8 million/year, the majority of this cost
resulting from collisions with birds. Further, bird strikes resulted in 101 human injuries
and 6 fatalities over the same time period (Cleary et al. 2002). Air travel is the fastestgrowing method of transportation, a trend that is expected to continue well into the future
(Lee et al. 2001). Therefore, it is important to conduct scientific studies to facilitate
development of sound management techniques to reduce air strikes (Sodhi 2002).
Diurnal raptors pose a potential strike threat to aircraft. Aircraft strikes involving
raptors often result in large amounts of damage due to the birds’ large body size and
propensity to fly at altitudes where aircraft are present (Thompson 1999). From 19902001, diurnal raptors (including Cathartidae and all Falconiformes) were the 3rd most
common bird group struck by U.S. civil aircraft (exceeded by gulls and doves) and the 3rd
most common group involved in strikes that resulted in aircraft damage (exceeded by
waterfowl and gulls, Cleary et al. 2002). The United States Air Force (USAF)
Bird/Wildlife Air Strike Hazard (BASH) team reports that turkey vultures (Cathartes
3
aura) were involved in 453 strikes with their aircraft from 1985-January 2003, making
them the 5th most commonly struck bird species (BASH stats website). Damage accrued
in strikes with turkey vultures totaled over $36 million, making them the 3rd most costly
species involved in aircraft strikes. Red-tailed hawks (Buteo jamaicensis), the 6th most
commonly struck species, were involved in 393 strikes. Damage accrued in strikes with
this species totaled over $14 million, making it the 6th most costly. Swainson’s hawks (B.
swainsoni) were struck 36 times, but were not ranked by number of strikes. However,
they were 22nd in cost, accruing over $1.2 million in damage. American kestrels (Falco
sparverius) were the 11th most frequently struck species with a total of 323 strikes, with
damage accrual of over $0.5 million, making them the 40th most costly species (BASH
stats website). Of 21 wildlife species or species groups ranked by relative hazard to
aircraft in the U.S., Dolbeer et al. (2000) concluded that vultures are the 2nd most
hazardous species group, hawks (Buteo spp.) ranked 8th, eagles 9th, and American kestrels
16th.
Some diurnal raptors are associated with prairie dog (Cynomys spp.) colonies.
This is especially well-documented for ferruginous hawks (B. regalis) and golden eagles
(Aquila chrysaetos), both of which have been deemed “dependent” on prairie dogs in a
weakly facultative sense by Kotliar et al. (1999). Due to widespread government and
private eradication efforts, habitat loss, the spread of sylvatic plague (Yersinia pestis),
and unregulated hunting, black-tailed prairie dogs (Cynomys ludovicianus) have
undergone a precipitous decline (Roemer and Forrest 1996, Barko 1997, Wuerthner 1997,
Van Putten and Miller 1999). Though they were once the most abundant mammalian
herbivore of the American Great Plains (Barko 1997, Wuerthner 1997), just over 630,000
4
ha of prairie dog occupied habitat, <2% of their historical range (Luce 2003), currently
exists. Due to the drastic decline of prairie dogs, persistence of threats, and lack of
protective measures for extant populations, the National Wildlife Federation petitioned
the US Fish and Wildlife Service to list black-tailed prairie dogs as threatened throughout
their range, as discussed in Van Putten and Miller (1999). Listing was found to be
warranted, but was precluded by other, higher priority issues (Gober 2000), leaving
black-tailed prairie dogs listed as a candidate species (U.S. Fish and Wildlife Service
2002).
Currently, control of black-tailed prairie dogs is used in some localities as a
method of raptor management to decrease strike risk (Robinette 1992, David Davis,
MBGR, personal communication). This is based on the premise that prairie dog colonies
attract raptors, thereby creating a higher air strike risk. However, previous studies
addressing raptor-prairie dog relationships have focused on wintering ferruginous hawks
(Schmutz and Fyfe 1987, Plumpton and Andersen 1997, 1998, Bak et al. 2001),
abundance of raptors during plague-induced prairie dog declines (Cully 1991, Seery and
Matiatos 2000), or the relative abundance of raptors at fixed-radius point count plots in
relation to plot distances from prairie dog colonies (Berry et al. 1998). Overall, these
studies leave a paucity of information for some raptor species and seasons, particularly
migratory periods which are associated with high bird strike risk (Burger 1985, Neubauer
1990, Sodhi 2002). Cully (1991) addressed raptor-prairie dog relationships during
migration; however, he did not separate this data from that of the summer season.
Additionally, previous studies examining prairie dog-raptor relationships were, by design,
only capable of identifying positive relationships between raptors and prairie dogs. No
5
studies have been conducted to address the possibility that some species may be more
abundant off colonies.
This study was conducted to: (1) quantify the relative abundance of raptors and
other large-bodied birds whose distribution may differ in relation to active black-tailed
prairie dog colonies and uncolonized grasslands; (2) describe species-specific patterns of
relative abundance of raptors at areas occupied and unoccupied by prairie dogs at
different sites; (3) determine if raptors are detected in flight proportionately more or less
frequently in association with prairie dog towns; and (4) use the preceding information to
determine if prairie dog control would potentially be effective in management of raptors
to reduce bird strike risk.
Methods
This study was conducted at 2 shortgrass prairie sites (Figure 2.1): (1) on and
within the vicinity of MBGR, a low-level F-16 bombing and strafing training site in eastcentral New Mexico; and (2) southern Lubbock County, Texas (LCTX). The 2 sites lie
within the Southern High Plains, roughly 190 km apart. Both sites are located within the
shortgrass prairie region and are characterized by a semiarid climate and flat topography.
However, they differ in that MBGR is predominantly rangeland, while agriculture,
especially cotton (Gossypium hirsutum) production, predominates in the LCTX area.
Colony plots in LCTX were generally more heavily grazed than non-colony sites.
We measured relative abundance of raptors using 300 m fixed-radius point counts
(Berry et al. 1998, Bak et al. 2001). At each study site, we established plots occupied by
active prairie dog colonies (colony plots) and grassland plots unoccupied by prairie dogs
6
(non-colony plots). Plots were separated by at least 1 km, and non-colony plots were
located at least 1 km from the nearest prairie dog colony. Each plot consisted of at least
50% grassland, and all were traversed by power lines and associated support structures to
assure that perch site availability was similar for all plots. Seven colony plots and 4 noncolony plots were located in LCTX, and 4 colony and 4 non-colony plots were located at
MBGR. At each site, we established a fixed route encompassing all points. The
direction the route was traversed was randomly assigned for each pair of morning and
evening surveys.
We conducted counts in the morning and evening, beginning 30 minutes after
sunrise and ending 30 minutes before sunset, respectively. Each count lasted
approximately 3-3.5 hours. We conducted equal numbers of morning and evening
surveys within each season. Data collection commenced immediately upon arrival at a
plot (Ralph et al. 1995: 169), at which time we recorded all raptors detected within 10
minutes. Counts were not conducted during rain or periods of wind-blown dust that
affected visibility. Cattle egrets (Bubulcus ibis), turkey vultures, burrowing owls (Athene
cunicularia), and Chihuahuan ravens (Corvus cryptoleucus), though dissimilar from
diurnal raptors taxonomically, were also recorded due to the potential strike hazard they
pose. We used an optical range finder to assure that birds located were within the 300m
radius. Lastly, we recorded activity (perched or in flight) at first detection for each
individual of every species under consideration except burrowing owls. Activity at first
detection was not collected for burrowing owls due to large numbers of birds often
detected (thus detracting from the chance of detecting birds of other species), especially
7
after the emergence of juveniles (Table 2.4), and because the low flight generally
exhibited by owls in daylight is unlikely to render them a significant air strike hazard.
Techniques for managing birds can be categorized as either short- (e.g., scare
tactics) or long-term (e.g., altering habitat to make it unsuitable for birds). Prairie dog
control as a method of altering raptor numbers constitutes a long-term management
action (Sodhi 2002). Thus, our data collection spanned a full year. We conducted all
counts in 2002: 14 counts at each plot in winter, 18 in spring migration, 24 in summer,
and 18 during fall migration. Delineation of seasons was based on dates used by
HawkWatch International (HawkWatch International website) to define migratory
periods at hawk watch sites in central New Mexico (winter: 6 November-23 February;
spring: 24 February-5 May; summer: 6 May-14 August; fall: 15 August-5 November).
We compared the seasonal and annual mean abundances of birds detected at
colony and non-colony plots at each study site with a one-way ANOVA. This was done
on a species-specific basis for those species detected ≥ 10 times, and then only for annual
or seasonal analyses for which ≥ 10 birds were detected. Additionally, analyses were
conducted for all birds pooled as an aggregate. The latter analysis included all detected
species except cattle egrets and burrowing owls, each of which display behaviors
markedly different from the remaining species (e.g., temporal activity period,
disinclination to soar, etc.), and thus pose a dissimilar strike risk. We tested assumptions
of normality and homoscedasticity with Shapiro-Wilk’s and Levene’s tests, respectively.
If variances were heterogeneous, we used Welch’s test instead of the standard F-test. If
data were non-normal, we compared distribution functions with a Kruskal-Wallis test of
ranks, though the results were interpreted as a comparison of means (Conover 1999).
8
We compared the percent of birds detected in flight at colony and non-colony
plots with a G-test (Sokal and Rohlf 1981). This was performed for individual species
for which adequate data was collected and all species as an aggregate on both a seasonal
and annual basis. All tests used an alpha level of 0.05 and were performed using SAS
software, version 8.2 (SAS Institute, Inc., Cary, North Carolina, USA). Power analysis
was conducted using StatSoft STATISTICA 5.5 (StatSoft, Inc., Tulsa, Oklahoma, USA).
We did not attempt to compare raptor numbers between the 2 sites due to differences in
geographical range of the raptor species involved, anthropogenic influences on the
landscape, and climatological differences.
Results
During the course of the study, we detected 12 species of diurnal raptor in
addition to cattle egrets, turkey vultures, burrowing owls, and Chihuahuan ravens
between the study sites (Table 2.1). Five diurnal raptor species, including northern
harrier (Circus cyaneus), Swainson’s hawk, red-tailed hawk, ferruginous hawk, and
American kestrel, were detected in sufficient numbers to allow analysis of individual
patterns of abundance in relation to prairie dog colonies. However, the remaining
species, Mississippi kite (Ictinia mississippiensis), Cooper’s hawk (Accipiter cooperii),
rough-legged hawk (B. lagopus), golden eagle, merlin (F. columbarius), peregrine falcon
(F. peregrinus), and prairie falcon (F. mexicanus), were included in aggregate analysis.
The power of statistical tests was generally fairly low (<75%), indicating that our study
design was unable to detect some statistical differences when results may, in fact, be
9
biologically meaningful. Therefore, we have reported results of statistically significant
tests as well as results of insignificant tests that we believe to be biologically important.
Lubbock County, Texas
We observed cattle egrets during spring, summer, and fall (Table 2.2). There was
no statistical difference in the distribution of cattle egrets between plot types, but
numerically they appeared to be more abundant at colony plots, especially during the
summer (Table 2.2). Cattle egrets were detected in flight less (G = 6.49; df = 1; P =
0.011) on colony plots (51.9% of birds in flight) than non-colony plots (90.0% of birds in
flight) in summer.
Turkey vultures were present in spring, summer, and fall, though in low numbers
during spring (Table 2.3). Turkey vultures were numerically more abundant at colony
plots annually and in fall (Table 2.3), though no statistical differences were found.
Additionally, we saw fewer turkey vultures in flight at colony plots (65.6%) than at noncolony plots (90.9%) in summer (G = 8.15; df = 1; P = 0.004), fall (37.7% and 82.1%,
respectively, G = 19.03; df = 1; P < 0.001), and over the entire year (48.7% and 87.1%,
respectively; G = 31.67; df = 1; P < 0.001).
Burrowing owls were significantly more abundant at colony than non-colony
plots in winter (Kruskal-Wallis, H = 5.66; df = 1; P = 0.017; Table 2.4), spring (KruskalWallis, H = 7.33; df = 1; P = 0.007; Table 2.4), summer (Kruskal-Wallis, H = 7.03; df =
1; P = 0.008; Table 2.4), and fall (Kruskal-Wallis, H = 7.37; df = 1; P = 0.007; Table
2.4), and over the entire year (Kruskal-Wallis, H = 7.03; df = 1; P = 0.008; Table 2.4).
10
We detected northern harriers in all seasons but summer (Table 2.5), Swainson’s
hawks in all seasons but winter, albeit in low numbers in spring and fall (Table 2.6), and
red-tailed hawks in all seasons, though in low numbers during summer (Table 2.7).
Northern harriers were more abundant and Swainson’s hawks less abundant at colony
plots, though differences were not significant. Red-tailed hawks appeared ubiquitous in
relative abundance at both plot types. Ferruginous hawks were not seen in summer, but
they were significantly more abundant at colony plots than non-colony plots in winter
(Kruskal-Wallis, H = 6.57; df = 1; P = 0.010; Table 2.8), and were numerically more
abundant at colony plots among seasons.
American kestrels were the only falconid present and numerous enough to
examine patterns of associations with prairie dogs in all seasons. Kestrels were
significantly more abundant at non-colony plots than at colony plots during spring
(Kruskal-Wallis, H = 5.99; df = 1; P = 0.014; Table 2.9), and fall (Kruskal-Wallis, H =
5.52; df = 1; P = 0.019; Table 2.9), as well as over the entire year (F = 6.84; df = 1, 9; P
= 0.028; Table 2.9). Overall, they were numerically more abundant at non-colony plots
in all seasons with the exception of winter (Table 2.9). Kestrels were detected in flight
more (G = 4.53; df = 1; P = 0.033) at colony plots (81.3%) than non-colony plots (37.5%)
in winter, as well as over the entire year (68.6% at colony, and 40% at non-colony plots,
respectively; G = 6.56; df = 1; P = 0.010).
We found no significant differences in mean abundance of total birds at colony
and non-colony plots. However, in a numerical sense, birds were slightly more abundant
at colony plots (Table 2.10). In fall, aggregate birds were detected in flight more (G =
9.03; df = 1; P = 0.003) at non-colony plots (58.1%) than colony plots (37.8%). On an
11
annual basis, aggregate birds were in flight more (G = 11.15; df = 1; P < 0.001) on noncolony plots (61.6%) than colony plots (48.3%).
The Range
We detected turkey vultures in spring, summer, and fall, though in low numbers
in all seasons (Table 2.3). In a numerical sense, vultures were less abundant at colony
plots. Burrowing owls were present in all seasons, though in low numbers in winter.
They were more abundant at colony than non-colony plots in all seasons, significantly in
spring (Kruskal-Wallis, H = 3.94; df = 1; P = 0.047; Table 2.4). We observed
Chihuahuan ravens in all seasons (Table 2.11). Statistically, they were equally abundant
at both plot types, though numerically they were more abundant at non-colony plots in
the fall (Table 2.11). However, on an annual basis, they were found in equal numbers at
both plot types (Table 2.11). Ravens were detected in flight more (G = 36.64; df = 1; P <
0.001) on colony plots (90%) than non-colony plots (55.8%) in summer, and over the
entire year (87.5% and 77.7% of birds in flight on colony and non-colony plots,
respectively, G = 12.65; df = 1; P < 0.001).
Northern harriers were present in winter, spring, and fall, though in low numbers
in winter. Harriers were numerically, but not statistically more abundant at colony plots
than non-colony plots among seasons. This pattern was especially pronounced in fall
(Table 2.5). Swainson’s hawks were present and significantly less abundant at colony
plots than non-colony plots in spring (F = 10.00; df = 1, 6; P = 0.020; Table 2.6), summer
(F = 14.55; df = 1, 6; P = 0.009; Table 2.6), and fall (Kruskal-Wallis, H = 4.98; df = 1; P
= 0.026; Table 2.6), as well as over the entire year (F = 23.70; df = 1, 6; P = 0.003; Table
12
2.6). Red-tailed hawks were present in spring, summer, and fall, albeit in low numbers in
all seasons. No significant differences or patterns were detected for this species (Table
2.7). Ferruginous hawks were present in all seasons, though in low numbers in spring
and summer. Though we did not find any statistically significant differences for this
species, they were numerically more abundant at colony plots among seasons (Table 2.8).
American kestrels were present in all seasons, but in low numbers in winter. They were
significantly more abundant at non-colony plots than at colony plots during spring
(Kruskal-Wallis, H = 4.05; df = 1; P = 0.044; Table 2.9), and fall (F = 6.38; df = 1, 6; P =
0.045; Table 2.9), as well as over the entire year (Welch’s, W = 25.92; df = 1, 5.04; P =
0.006; Table 2.9). Overall, they were numerically more abundant at non-colony plots in
all seasons. Kestrels were detected in flight more at colony plots than non-colony plots in
summer (66.7% and 12.5%, respectively; G = 4.58; df = 1; P = 0.032).
Similar to LCTX, no significant differences were detected between mean
abundance of total birds at colony and non-colony plots. Numerically, birds were slightly
more abundant at non-colony plots (Table 2.10). Total birds were detected in flight more
(G = 61.06; df = 1; P < 0.001) on colony plots (85.0%) than non-colony plots (46.2%) in
summer. On an annual basis, aggregate birds were in flight more (G = 24.66; df = 1; P <
0.001) at colony plots (80.2%) than non-colony plots (67.0%).
Discussion
We detected 9 species frequently enough to analyze of patterns of abundance.
Cattle egrets, turkey vultures, northern harriers, Swainson’s hawks, ferruginous hawks,
American kestrels, and burrowing owls exhibited some degree of differential abundance
13
with respect to presence or absence of prairie dogs. Six of these 7 species displayed
similar patterns of abundance in relation to treatment among sites and seasons. The
patterns of abundance observed for turkey vultures at the 2 plot types were slightly less
clear, and we did not detect any differences in red-tailed hawk or Chihuahuan raven
abundances with respect to presence or absence of prairie dog colonies.
Cattle egrets were found only at the LCTX site, and were more common at prairie
dog colonies. The difference in abundance of cattle egrets between plot types was
greatest in the summer, and the birds were detected in flight less on colony than on noncolony plots. This possibly lessens the overall risk of these birds in relation to prairie dog
colonies. However, cattle egrets were weakly associated with prairie dogs, and therefore
may pose an increased strike risk in the presence of colonies.
Cattle egrets are insectivorous (Telfair 1994), and may be more common at
colony plots due to higher abundances of insects on colonies compared to uncolonized
grasslands in spring and summer (Olson 1985, McCaffrey 2001, Russell and Detling in
press). However, both Russell and Detling (in press) and O’Meilia et al. (1982) found
that grasshopper densities were higher off colonies in August, suggesting a shift in habitat
use by grasshoppers in late summer. Cattle egrets showed a decrease in the proportion of
birds at colony plots between summer and fall, suggesting that the shift in grasshoppers
may have affected their selection of foraging sites. Cattle egrets are often found in
association with livestock, taking advantage of the invertebrates that they disturb (Telfair
1994). Therefore, the egrets may be responding more to the stocking density of the 2 plot
types than to the presence or absence of prairie dogs.
14
Turkey vultures appeared to be numerically more abundant at colony plots,
especially during fall migration when the birds were most abundant. During summer, the
only other season these birds were present in substantial numbers, they were found in
nearly equal abundance at both plot types. Fewer birds were detected in flight on
colonies than off in LCTX. This suggests that despite their generally higher abundance at
colony plots in LCTX, the fact that vultures are detected in flight proportionately less on
colonies may, to some extent, mitigate the strike risk of this species near prairie dog
colonies.
Interpreting patterns of vulture occurrence proved somewhat difficult. Over the
entire year, turkey vultures were more abundant at colony plots in LCTX. In contrast,
they were more abundant at non-colony plots at MBGR, though they were numerically
less abundant than at LCTX. The 2 plots nearest a vulture roost site in LCTX accounted
for 66.7% of occurrences of detecting 4 or more vultures in flight at a given plot. This
suggests that the juxtaposition of these plots to the roost site may have biased counts and
inflated the proportion of birds detected at colony plots.
Turkey vultures may also be more common at prairie dog colonies in the fall
because they feed on prey remains left by other raptors (Berry et al. 1998). Raptors
capable of killing prey larger than they can consume at one feeding are uncommon in
LCTX during the summer. This could explain why vultures are only slightly more
common at colony plots in that season. Turkey vultures were detected in flight less on
colonies in summer and fall. This could result from groups of birds feeding on kill
remains on prairie dog colonies (Kirk and Mossman 1998). However, we cannot provide
a clear answer to strike risk posed by turkey vultures with respect to presence or absence
15
of prairie dog colonies. Given the disproportionately high risk this species poses to
aircraft (Dolbeer et al. 2000), more work is needed to explore any possible relationship of
this species with prairie dogs before any definite recommendations can be made.
Northern harriers were generally more abundant at colony plots, especially at
MBGR, though this was not validated statistically. Based on these results, harriers show
a weak association with prairie dog colonies, and are more likely to pose a strike risk in
their presence.
Swainson’s hawks were clearly more abundant at non-colony plots. Abundance
of cottontail rabbits, small mammals, reptiles, and amphibians is generally higher or
similar on prairie dog colonies when compared to uncolonized sites (Dano 1952,
O’Meilia et al. 1982, Agnew et al. 1986, Barko et al. 1999, Ceballos et al. 1999, Kretzer
and Cully 2001, McCaffrey 2001). Prairie dog colonies are characterized by decreased
vegetative height and density (Coppock et al. 1983, Agnew et al. 1986, Archer et al.
1987, Weltzin et al. 1997, Winter et al. 2002). Bechard (1982) reported that visibility of
prey in relation to vegetative cover was a more important factor than overall prey density
in selection of hunting sites for Swainson’s hawks. Berry et al. (1998) found that roughlegged hawks were associated with colonies, and speculated that it could be due, in part,
to the prominence of prey in the scant vegetation on colonies. Bechard’s (1982) results,
coupled with the relative abundance and general vulnerability of prey on prairie dog
colonies, intuitively suggest that prairie dog colonies would be preferred hunting sites for
Swainson’s hawks. However, non-breeding Swainson’s hawks are believed to be
primarily insectivorous and large insects constitute the majority of prey taken (Johnson et
al. 1987, Jaramillo 1993). The abundance of grasshoppers off prairie dog colonies in late
16
summer and the insectivorous nature of post-breeding and fall migrant Swainson’s hawks
may, in part, be responsible for the increased abundance of Swainson’s hawks at noncolony plots during that time period. However, during the breeding season, Swainson’s
hawks prey primarily on mammals, and to a lesser extent, birds and reptiles (England et
al. 1997), so their association with non-colony plots during that season is still perplexing.
Prairie dog burrows provide an abundance of escape cover for potential vertebrate prey
organisms such as lagomorphs and other species of ground squirrels (Koford 1958, Smith
1958, Ceballos et al. 1999). Additionally, the antipredator call and sudden movement of
escaping prairie dogs in the presence of a hunting Swainson’s hawk may serve to alert
potential prey organisms. Therefore, prey capture success might be much lower on
colonies, causing the birds to concentrate hunting effort off colonies. Whatever the
reason, our data suggest that Swainson’s hawks are strongly dissociated with prairie dog
colonies, and therefore present a comparatively lower strike risk where colonies are
present.
Ferruginous hawks were significantly more abundant at prairie dog colonies in
winter in LCTX, which is concurrent with the results of previous studies addressing the
wintering ecology of this species (Schmutz and Fyfe 1987, Cully 1991, Plumpton and
Andersen 1997, 1998, Berry et al. 1998, Seery and Matiatos 2000, Bak et al. 2001). This
indicates that wintering ferruginous hawks are strongly associated with prairie dog
colonies, probably due to the fact that prairie dogs are among their most important winter
prey species (Schmutz and Fyfe 1987, Bechard and Schmutz 1995, Plumpton and
Andersen 1997, 1998). However, despite the fact that ferruginous hawks were
numerically more abundant at colony plots in all seasons that they were present at both
17
sites, no other significant differences were detected. This suggests that the association of
ferruginous hawks with prairie dog colonies may be more pronounced in winter than in
migration. Overall, ferruginous hawks display a strong association with prairie dog
colonies, and potentially pose a greater strike risk in the presence rather than absence of
colonies.
American kestrels were overall more common at non-colony than colony plots,
likely for reasons similar to the Swainson’s hawk. However, this difference was more
distinctive and statistically significant only in migratory periods (spring and fall),
suggesting some seasonality to this phenomenon. They were detected in flight more at
colony plots than at non-colony plots, which may decrease the risk they pose at noncolony plots to some degree. However, kestrels are strongly dissociated with prairie dog
colonies, and pose a potentially greater strike risk in the absence of prairie dog colonies.
Burrowing owls were clearly more abundant at colony plots. This is consistent
with previous studies (Butts and Lewis 1982), and together with other studies examining
the relationship between burrowing owls and prairie dogs, implies that burrowing owls
are strongly associated with prairie dog colonies (Winter 1999, Desmond et al. 2000,
Sidle et al. 2001). From the standpoint of air strikes, this suggests that burrowing owls
are an increased risk in the presence of prairie dog colonies. The point count
methodology used in this study was presumably unable to detect all burrowing owls at a
given plot, due to the fact that additional owls were likely underground. However, due to
the abundance of available burrows at prairie dog colonies, it is more likely that the
number of owls was under-estimated at colony plots than at non-colony plots. Therefore,
the already distinctive observed difference in numbers of burrowing owls at the 2 plot
18
types is probably less than the actual difference, further supporting the strong association
of burrowing owls with prairie dogs.
Red-tailed hawks and Chihuahuan ravens were detected in equal numbers at both
plot types. This is especially important considering the high strike risk presented by redtailed hawks. Chihuahuan ravens were also detected in flight more on prairie dog
colonies. However, this probably does not substantially increase the strike risk posed by
this species, especially when the actual percentages of birds detected in flight (87.5% and
77.7% on and off colonies, respectively) are considered.
When all species are pooled and analyzed as an aggregate, the 2 study sites
yielded somewhat contrasting results. Numerically, there were more birds at colony plots
at LCTX, more at non-colony plots at MBGR. However, birds were detected in flight
more at non-colony than at colony plots at LCTX, while they were detected in flight less
at non-colony plots at MBGR. For both sites, the plot type that supports more birds is
also the plot type that experiences birds in flight less than the other. Therefore, even the
slight numerical differences are mitigated to a degree, as more birds at one plot type do
not necessarily increase strike risk if those birds are less likely to be in flight.
The preceding information indicates that northern harriers are weakly associated
with prairie dog colonies, while ferruginous hawks and burrowing owls show a strong
association. These species may pose an increased strike risk in the presence of prairie
dogs. Conversely, Swainson’s hawks and American kestrels are strongly dissociated
with colonies, and thus pose less strike risk in their presence.
When species are pooled, aggregate analysis indicates that prairie dog control is
unlikely to have any effect, positive or negative, on air strike risk presented by all birds.
19
However, in order to fully evaluate the strike hazard presented by these species in
relation to prairie dogs, some additional aspects of strike risk assessment must be
considered.
Bird species differ in their potential hazard to aircraft (Burger 1985, Dolbeer et al.
2000, Sodhi 2002). Dolbeer et al. (2000) ranked wildlife species and species groups by
their relative hazard to aircraft. Their intention was to provide guidelines to airport
operators enabling them to effectively allocate management effort to those species that
are more hazardous to aircraft. Using our results and bird strike hazard literature, we will
similarly formulate recommendations for the species in this study with respect to the
relative risk they pose in the presence of prairie dog colonies, and how management
effort should accordingly be allocated.
On a scale of 1-100, Dolbeer et al. (2000) assigned vultures a hazard ranking of
63 (the only taxon ranking higher was deer at 100), Buteo hawks 25, herons 22, owls 16,
American kestrel 14, and crows/ravens 12. When USAF data are considered (BASH
stats website), the total cost of damage accrued in strikes with a species per total number
of individuals of that species struck (cost/count) is a more useful metric of individual
species strike risk than overall cost or number struck. Of species in this study, red-tailed
hawks incur an average of $35,691/individual struck, $33,646 for Swainson’s hawks, and
$1,581 for American kestrels. In this relative sense, it is clear that Buteo hawks are a
much higher strike risk than American kestrels.
Despite their fairly broad geographical range (MacWhirter and Bildstein 1996),
large body size, and the fact that they are often common on airfields (Burger 1985),
northern harriers were not ranked by Dolbeer et al. (2000) or included in data provided by
20
the USAF BASH team (BASH stats website). This indicates that harriers are generally
not a significant strike risk. Some attribute this to the possibility that harriers are more
adept at avoiding aircraft than other species (Burger 1985), though as Sodhi (2002) points
out, concrete evidence for this hypothesis is lacking. Therefore, despite the fact that they
are weakly associated with prairie dog colonies, harriers are probably not a species
worthy of much concern in consideration of controlling prairie dogs for raptor
management.
Swainson’s hawks show a strong dissociation with prairie dog colonies and pose a
high general strike risk in relation to the other species considered here. Therefore,
controlling prairie dogs is not likely to decrease the strike risk posed by Swainson’s
hawks; rather, control of prairie dogs and conversion of former colonies to grasslands
may actually increase strike risk. In contrast, ferruginous hawks display a strong
association with prairie dog colonies. Therefore, prairie dog control may be an effective
method of reducing numbers of ferruginous hawks at a site and, thereby, reducing strike
risk.
Despite their strong dissociation with prairie dog colonies, American kestrels pose
a low strike hazard. Though Dolbeer et al. (2000) indicate that “owls” as a group pose
some risk to aircraft, burrowing owls are not included in BASH stats. Additionally, FAA
bird strike data provided by Cleary et al. (2002) show that burrowing owls comprise only
4.6% of identified owls that were reported as struck by US civil aircraft between 19902001. Therefore, burrowing owls as a species seem to pose little overall threat to aircraft,
despite their strong association with prairie dog colonies.
21
When the general strike risk posed by a species is coupled with the relationship of
that species with prairie dog colonies, we conclude that in the presence of prairie dog
colonies, cattle egrets present a moderately increased risk, ferruginous hawks a highly
increased risk, and Swainson’s hawks a highly decreased risk. The previously stated
conclusions suggest differing management recommendations for the 2 sites. In LCTX,
ferruginous hawks are far more abundant than Swainson’s hawks (Table 2.10). This
suggests that prairie dog control may reduce the overall strike risk at that site. In
contrast, Swainson’s hawks are more abundant than ferruginous hawks at MBGR (cattle
egrets were not present). Therefore, prairie dog control would likely be ineffective in
reduction of air strike risk at that site, and could possibly be detrimental.
Based strictly on numbers of raptors seen in relation to prairie dog colonies, it
seems that prairie dog control would be ineffective in altering diurnal raptor numbers or
strike risks at either site. However, when the relative abundance and strike risk of the
species present are considered, it appears that controlling prairie dogs may be an effective
method for reduction of air strike risk in LCTX, but may increase risk at MBGR. This
demonstrates that assessment of wildlife strike risk must be conducted on a site-specific
basis, as recommended by Dolbeer et al. (2000). They recommend that at a given site,
wildlife surveys must be conducted to determine the relative abundance of each species.
Using that information and the relative strike risk presented by each species, effort and
resources expended to reduce strike hazard can be allocated to the most important species
at that site, thus increasing efficacy of management efforts.
22
Literature Cited
Agnew, W., D. W. Uresk, and R. M. Hansen. 1986. Flora and fauna associated with
prairie dog colonies and adjacent ungrazed mixed-grass prairie in western South
Dakota. Journal of Range Management 39: 135-139.
Archer, S., M. G. Garrett, and J. K. Detling. 1987. Rates of vegetation change associated
with prairie dog (Cynomys ludovicianus) grazing in North American mixed-grass
prairie. Vegetatio 72: 159-166.
Bak, J. M., K. G. Boykin, B. C. Thompson, and D. L. Daniel. 2001. Distribution of
wintering ferruginous hawks (Buteo regalis) in relation to black-tailed prairie dog
(Cynomys ludovicianus) colonies in southern New Mexico and northern Chihuahua.
Journal of Raptor Research 35: 124-129.
Barko, V. A. 1997. History of policies concerning the black-tailed prairie dog: a review.
Proceedings of the Oklahoma Academy of Science 77: 27-33.
Barko, V. A., J. H. Shaw, and D. M. Leslie. 1999. Birds associated with black-tailed
prairie dog colonies in southern shortgrass prairie. Southwestern Naturalist 44: 484489.
BASH Stats website: http://safety.kirtland.af.mil/AFSC/Bash/stats.html. Last accessed
27 July 2003.
Bechard, M. J. 1982. Effect of vegetative cover on foraging site selection by Swainson’s
hawk. Condor 84: 153-159.
Bechard, M. J., and J. K. Schmutz. 1995. Ferruginous hawk. Number 172 in A. Poole
and F. Gill, editors. The Birds of North America.
Berry, M. E., C. E. Bock, and S. L. Haire. 1998. Abundance of diurnal raptors on open
space grasslands in an urbanized landscape. Condor 100: 601-608.
Burger, J. 1985. Factors affecting bird strikes on aircraft at a coastal airport. Biological
Conservation 33: 1-28.
Butts, K. O., and J. C. Lewis. 1982. The importance of prairie dog towns to burrowing
owls in Oklahoma. Proceedings of the Oklahoma Academy of Science 62: 46-52.
Ceballos, G., J. Pacheco, and R. List. 1999. Influence of prairie dogs (Cynomys
ludovicianus) on habitat heterogeneity and mammalian diversity in Mexico. Journal
of Arid Environments 41: 161-172.
23
Cleary, E. C., R. A. Dolbeer, and S. E. Wright. 2002. Wildlife strikes to civil aircraft in
the United States 1990-2001. Federal Aviation Administration National Wildlife
Strike Database Serial Report number 8.
Conover, W. J. 1999. Practical nonparametric statistics. Third edition. John Wiley and
Sons, New York, New York, USA.
Coppock, D. L., J. K. Detling, J. E. Ellis, and M. I. Dyer. 1983. Plant-herbivore
interactions in a North American mixed-grass prairie: I. Effects of black-tailed
prairie dogs on intraseasonal aboveground plant biomass and nutrient dynamics and
plant species diversity. Oecologia 56: 1-9.
Cully, J. F. 1991. Response of raptors to reduction of a Gunnison’s prairie dog
population by plague. American Midland Naturalist 125: 140-149.
Dano, L. 1952. Cottontail rabbit (Sylvilagus audubonii baileyi) populations in relation to
prairie dog (Cynomys ludovicianus ludovicianus) towns. Thesis, Colorado State
University, Fort Collins, Colorado, USA.
Desmond, M. J., J. A. Savidge, and K. M. Eskridge. 2000. Correlations between
burrowing owl and black-tailed prairie dog declines: a 7-year analysis. Journal of
Wildlife Management 64: 1067-1075.
Dolbeer, R. A., S. E. Wright, and E. C. Cleary. 2000. Ranking the hazard level of
wildlife species to aviation. Wildlife Society Bulletin 28: 372-378.
England, A. S., M. J. Bechard, and C. S. Houston. 1997. Swainson’s hawk. Number
265 in A. Poole and F. Gill, editors. The Birds of North America. The Academy of
Natural Sciences, Philadelphia, Pennsylvania, USA.
Gober, P. 2000. Endangered and threatened wildlife and plants; 12-month finding for a
petition to list the black-tailed prairie dog as threatened. Federal register 65: 54765488.
HawkWatch International website: http://www.hawkwatch.org. Last accessed 5 August,
2003.
Jaramillo, A. P. 1993. Wintering Swainson’s hawks in Argentina: food and age
segregation. Condor 95: 475-479.
Johnson, C. G., L. A. Nickerson, and M. J. Bechard. 1987. Grasshopper consumption
and summer flocks of nonbreeding Swainson’s hawks. Condor 89: 676-678.
24
Kirk, D. A., and M. J. Mossman. 1998. Turkey vulture. Number 339 in A. Poole and F.
Gill, editors. The Birds of North America. The Academy of
Natural Sciences, Philadelphia, Pennsylvania, USA.
Koford, C. B. 1958. Prairie dogs, whitefaces, and blue grama. Wildlife Monographs: 3.
Kotliar, N. B., B. W. Baker, A. D. Whicker, and G. Plumb. 1999. A critical review of
assumptions about the prairie dog as a keystone species. Environmental Management
24: 177-192.
Kretzer, J. E., and Cully, J. F. 2001. Effects of black-tailed prairie dogs on reptiles and
amphibians in Kansas shortgrass prairie. Southwestern Naturalist 46: 171-177.
Lee, J. J., S. P. Lukachko, I. A. Waitz, and A. Schafer. 2001. Historical and future
trends in aircraft performance, cost, and emissions. Annual Review of Energy and
the Environment 26: 167-200.
Luce, R. J. 2003. A multi-state conservation plan for the black-tailed prairie dog,
Cynomys ludovicianus, in the United States – an addendum to the black-tailed prairie
dog conservation assessment and strategy, November 3, 1999.
MacWhirter, R. B., and K. L. Bildstein. 1996. Northern harrier. Number 210 in A.
Poole and F. Gill, editors. The Birds of North America. The Academy of
Natural Sciences, Philadelphia, Pennsylvania, USA.
McCaffrey, R. E. 2001. Biodiversity associated with active and extirpated black-tailed
prairie dog colonies. Thesis, Texas Tech University, Lubbock, Texas, USA.
Neubauer, J. C. 1990. Why birds kill: cross-sectional analysis of U.S. Air Force bird
strike data. Aviation, Space, and Environmental Medicine 61: 343-348.
Olson, S. L. 1985. Mountain plover food items on and adjacent to a prairie dog town.
Prairie Naturalist 17: 83-90.
O’Meilia, M. E., F. L. Knopf, and J. C. Lewis. 1982. Some consequences of competition
between prairie dogs and beef cattle. Journal of Range Management 35: 580-585.
Plumpton, D. L., and D. E. Andersen. 1997. Habitat use and time budgeting by
wintering ferruginous hawks. Condor 99: 888-893.
Plumpton, D. L., and D. E. Andersen. 1998. Anthropogenic effects on winter behavior
of ferruginous hawks. Journal of Wildlife Management 62: 340-346.
Ralph, C. J., J. R. Sauer, and S. Droege, technical editors. 1995. Monitoring bird
populations by point counts. U.S. Forest Service General Technical Report 149.
25
Robinette, K. W. 1992. Black-tailed prairie dog management: translocation and barriers.
Thesis, Colorado State University, Fort Collins, Colorado, USA.
Roemer, D. M., and S. C. Forrest. 1996. Prairie dog poisoning in northern Great Plains:
an analysis of programs and policies. Environmental Management: 20: 349-359.
Russell, R. E., and J. K. Detling. In press. Grasshoppers (Orthoptera:Acrididae) and
black-tailed prairie dogs (Sciuridae:Cynomys ludovicianus)(Ord): associations
between two rangeland herbivores. Journal of the Kansas Entomological Society.
Schmutz, J. K., and R. W. Fyfe. 1987. Migration and mortality of Alberta ferruginous
hawks. Condor 89: 169-174.
Seery, D. B., and D. J. Matiatos. 2000. Response of wintering Buteos to plague
epizootics in prairie dogs. Western North American Naturalist 60: 420-425.
Sidle, J. G., M. Ball, T. Byer, J. J. Chynoweth, G. Foli, R. Hodorff, G. Moravek, R.
Peterson, and D. N. Svingen. 2001. Occurrence of burrowing owls in black-tailed
prairie dog colonies on Great Plains National Grasslands. Journal of Raptor Research
35: 316-321.
Smith, R. E. 1958. Natural history of the prairie dog in Kansas. University of Kansas
Museum of Natural History and State Biological Survey Miscellaneous Publication
16.
Sodhi, N. S. 2002. Competition in the air: birds versus aircraft. Auk 119: 587-595.
Sokal, R. R., and F. J. Rohlf. 1981. Biometry. Second edition. W. H. Freeman and
Company, San Francisco, California, USA.
Telfair, R. C. 1994. Cattle egret. Number 113 in A. Poole and F. Gill, editors. The
Birds of North America. The Academy of
Natural Sciences, Philadelphia, Pennsylvania, USA.
Thompson, M. M. 1999. Using a GIS to integrate seasonal raptor distributions into a
bird avoidance model for aircraft. Journal of Raptor Research 33: 53-58.
U.S. Fish and Wildlife Service. 2002. Endangered and Threatened Wildlife and Plants.
Federal register 67: 40657-40679.
Van Putten, M., and S. D. Miller. 1999. Prairie dogs: the case for listing. Wildlife
Society Bulletin 27: 1110-1120.
26
Weltzin, J. F., S. L. Dowhower, and R. K. Heitschmidt. 1997. Prairie dog effects on
plant community structure in southern mixed-grass prairie. Southwestern Naturalist
42: 251-258.
Winter, S. L. 1999. Plant and breeding bird communities of black-tailed prairie dog
colonies and non-colonized areas in southwest Kansas and southeast Colorado.
Thesis, Kansas State University, Manhattan, Kansas, USA.
Winter, S. L., J. F. Cully, and J. S. Pontius. 2002. Vegetation of prairie dog colonies and
non-colonized short-grass prairie. Journal of Range Management 55: 502-508.
Wuerthner, G. 1997. Viewpoint: the black-tailed prairie dog – headed for extinction?
Journal of Range Management 50: 459-466.
27
New Mexico
Texas
Lubbock County, TX
Melrose Bombing and
Gunnery Range
200
0
200
400
600
800
1000 Kilometers
Figure 2.1. Location of study sites for point counts conducted in 2002, including Melrose
Bombing and Gunnery Range in Roosevelt County, New Mexico, and southern Lubbock
County, Texas.
28
Table 2.1. Presence (denoted by an “X”) or absence of birds at Lubbock County, Texas
(LCTX) and Melrose Bombing and Gunnery Range (Range), Roosevelt County, New
Mexico, as determined by point counts in 2002.
Species
LCTX
Cattle egret
X
Turkey vulture
X
Mississippi kite
X
Northern harrier
X
Cooper’s hawk
X
Swainson’s hawk
X
X
Red-tailed hawk
X
X
Ferruginous hawk
X
X
Rough-legged hawk
X
X
Golden eagle
X
X
American kestrel
X
X
Merlin
Range
X
X
X
Peregrine falcon
X
Prairie falcon
X
X
Burrowing owl
X
X
Chihuahuan raven
X
X
29
Table 2.2. Mean number of cattle egrets detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and non-colony plots in
Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR)
in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
1.347
0.463
0.462a
Non-colony
296
0.834
0.316
Colony
98
0
0
Non-colony
56
0
0
Colony
126
0.135
0.135
Non-colony
72
0
0
Colony
168
1.125
0.537
Non-colony
96
0.104
0.055
Colony
126
3.905
1.845
Non-colony
72
3.292
1.234
Colony
296
0
0
Non-colony
296
0
0
Colony
56
0
0
Non-colony
56
0
0
Colony
72
0
0
Non-colony
72
0
0
Colony
96
0
0
Non-colony
96
0
0
Colony
72
0
0
Non-colony
72
0
0
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Kruskal-Wallis test.
30
0.450b
0.195a
0.849b
Table 2.3. Mean number of turkey vultures detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and non-colony plots in
Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR)
in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
0.365
0.152
0.493a
Non-colony
296
0.209
0.097
Colony
98
0
0
Non-colony
56
0
0
Colony
126
0.048
0.048
Non-colony
72
0.014
0.014
Colony
168
0.363
0.128
Non-colony
96
0.344
0.163
Colony
126
0.968
0.469
Non-colony
72
0.389
0.186
Colony
296
0.014
0.006
Non-colony
296
0.034
0.007
Colony
56
0
0
Non-colony
56
0
0
Colony
72
0.014
0.014
Non-colony
72
0.028
0.028
Colony
96
0.031
0.010
Non-colony
96
0.052
0.020
Colony
72
0
0
Non-colony
72
0.042
0.014
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Kruskal-Wallis test.
31
0.779b
0.928a
0.924b
0.069b
0.850b
0.350b
0.040b
Table 2.4. Mean number of burrowing owls detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and non-colony plots in
Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR)
in 2002. All reported statistics were calculated using a Kruskal-Wallis test.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
6.151
1.025
0.008
Non-colony
296
0.044
0.035
Colony
98
0.337
0.124
Non-colony
56
0
0
Colony
126
2.754
0.665
Non-colony
72
0
0
Colony
168
2.363
2.363
Non-colony
96
0.135
0.109
Colony
126
6.135
0.709
Non-colony
72
0
0
Colony
296
1.510
0.932
Non-colony
296
0.007
0.007
Colony
56
0.018
0.018
Non-colony
56
0
0
Colony
72
1.361
0.787
Non-colony
72
0
0
Colony
96
3.375
2.115
Non-colony
96
0.021
0.021
Colony
72
0.333
0.297
Non-colony
72
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
32
0
0
0.017
0.007
0.008
0.007
0.091
0.317
0.047
0.091
0.131
Table 2.5. Mean number of northern harriers detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and non-colony plots in
Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR)
in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
0.125
0.032
0.462a
Non-colony
296
0.088
0.032
Colony
98
0.184
0.058
Non-colony
56
0.161
0.034
Colony
126
0.246
0.064
Non-colony
72
0.125
0.062
Colony
168
0
0
Non-colony
96
0
0
Colony
126
0.127
0.040
Non-colony
72
0.111
0.075
Colony
296
0.101
0.034
Non-colony
296
0.024
0.016
Colony
56
0.054
0.034
Non-colony
56
0.018
0.018
Colony
72
0.125
0.014
Non-colony
72
0.056
0.039
Colony
96
0
0
Non-colony
96
0
0
Colony
72
0.250
0.151
Non-colony
72
0.028
0.016
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Kruskal-Wallis test.
33
0.787a
0.246a
0.840a
0.085a
0.405b
0.178b
0.225b
Table 2.6. Mean number of Swainson’s hawks detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and non-colony plots in
Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR)
in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
0.014
0.007
0.078b
Non-colony
296
0.047
0.020
Colony
98
0
0
Non-colony
56
0
0
Colony
126
0.016
0.010
Non-colony
72
0.056
0.039
Colony
168
0.018
0.012
Non-colony
96
0.094
0.055
Colony
126
0.016
0.016
Non-colony
72
0.014
0.014
Colony
296
0.074
0.034
Non-colony
296
0.389
0.055
Colony
56
0
0
Non-colony
56
0
0
Colony
72
0.083
0.048
Non-colony
72
0.361
0.073
Colony
96
0.146
0.063
Non-colony
96
0.781
0.154
Colony
72
0.028
0.028
Non-colony
72
0.194
0.036
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Kruskal-Wallis test.
34
0.375b
0.120b
0.779b
0.003a
0.020a
0.009a
0.026b
Table 2.7. Mean number of red-tailed hawks detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and non-colony plots in
Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR)
in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
0.141
0.034
0.989a
Non-colony
296
0.142
0.068
Colony
98
0.265
0.081
Non-colony
56
0.232
0.054
Colony
126
0.183
0.063
Non-colony
72
0.153
0.076
Colony
168
0.006
0.006
Non-colony
96
0.010
0.010
Colony
126
0.183
0.072
Non-colony
72
0.236
0.182
Colony
296
0.027
0.015
Non-colony
296
0.014
0.010
Colony
56
0
0
Non-colony
56
0
0
Colony
72
0.014
0.014
Non-colony
72
0.014
0.014
Colony
96
0.010
0.010
Non-colony
96
0.021
0.021
Colony
72
0.083
0.053
Non-colony
72
0.014
0.014
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Kruskal-Wallis test.
35
0.781a
0.619b
0.673b
0.847b
0.468a
1.000b
0.850b
0.321b
Table 2.8. Mean number of ferruginous hawks detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and non-colony plots in
Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR)
in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
0.280
0.104
0.088b
Non-colony
296
0.064
0.032
Colony
98
0.776
0.285
Non-colony
56
0.107
0.046
Colony
126
0.357
0.161
Non-colony
72
0.139
0.092
Colony
168
0
0
Non-colony
96
0
0
Colony
126
0.190
0.081
Non-colony
72
0.042
0.014
Colony
296
0.135
0.047
Non-colony
296
0.068
0.021
Colony
56
0.143
0.051
Non-colony
56
0.107
0.046
Colony
72
0.028
0.016
Non-colony
72
0.028
0.028
Colony
96
0.010
0.010
Non-colony
96
0.010
0.010
Colony
72
0.403
0.148
Non-colony
72
0.153
0.035
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Kruskal-Wallis test.
36
0.010b
0.253b
0.136b
0.240a
0.620a
0.739b
1.000b
0.151a
Table 2.9. Mean number of American kestrels detected at n plots (number of surveys X
number of plots) on a seasonal and annual (year) basis at colony and non-colony plots in
Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR)
in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
0.068
0.021
0.028a
Non-colony
296
0.152
0.020
Colony
98
0.163
0.046
Non-colony
56
0.143
0.101
Colony
126
0.056
0.021
Non-colony
72
0.222
0.075
Colony
168
0.036
0.017
Non-colony
96
0.063
0.021
Colony
126
0.048
0.031
Non-colony
72
0.208
0.035
Colony
296
0.051
0.022
Non-colony
296
0.006b
0.010
Colony
56
0.018
0.018
Non-colony
56
0.071
0.051
Colony
72
0.042
0.014
Non-colony
72
0.111
0.023
Colony
96
0.063
0.050
Non-colony
96
0.083
0.083
Colony
72
0.069
0.035
Non-colony
72
0.431
0.139
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Welch’s test.
c
Results from Kruskal-Wallis test.
37
0.837a
0.014c
0.326c
0.019c
0.006b
0.405c
0.044c
0.741c
0.045a
Table 2.10. Mean number of all birds detected at n plots (number of surveys X number
of plots) on a seasonal and annual (year) basis at colony and non-colony plots in Lubbock
County, Texas (LCTX) and at Melrose Bombing and Gunnery Range (MBGR) in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
1.039
0.227
0.416a
Non-colony
296
0.740
0.233
Colony
98
1.408
0.302
Non-colony
56
0.643
0.189
Colony
126
1.016
0.217
Non-colony
72
0.764
0.244
Colony
168
0.423
0.137
Non-colony
96
0.563
0.208
Colony
126
1.595
0.523
Non-colony
72
1.028
0.353
Colony
296
1.716
0.193
Non-colony
296
1.997
0.115
Colony
56
0.911
0.279
Non-colony
56
0.964
0.156
Colony
72
2.556
0.264
Non-colony
72
2.389
0.348
Colony
96
1.740
0.645
Non-colony
96
1.938
0.092
Colony
72
1.472
0.422
Non-colony
72
2.486
0.381
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Kruskal-Wallis test.
38
0.109a
0.482a
0.573a
0.571b
0.259a
0.872a
0.716a
0.772a
0.125a
Table 2.11. Mean number of Chihuahuan ravens detected at n plots (number of surveys
X number of plots) on a seasonal and annual (year) basis at colony and non-colony plots
in Lubbock County, Texas (LCTX) and at Melrose Bombing and Gunnery Range
(MBGR) in 2002.
Site
Season
Plot type
n
x̄
SE
P
LCTX
Year
Colony
518
0
0
0.186c
Non-colony
296
0.003
0.003
Colony
98
0
0
Non-colony
56
0
0
Colony
126
0
0
Non-colony
72
0
0
Colony
168
0
0
Non-colony
96
0.010
0.010
Colony
126
0
0
Non-colony
72
0
0
Colony
296
1.267
0.144
Non-colony
296
1.284
0.173
Colony
56
0.625
0.263
Non-colony
56
0.732
0.223
Colony
72
2.222
0.254
Non-colony
72
1.792
0.400
Colony
96
1.458
0.596
Non-colony
96
0.990
0.152
Colony
72
0.556
0.143
Non-colony
72
1.597
0.411
Winter
Spring
Summer
Fall
MBGR
Year
Winter
Spring
Summer
Fall
a
Results from one-way ANOVA.
b
Results from Welch’s test.
c
Results from Kruskal-Wallis test.
39
0.186c
0.943a
0.767a
0.399a
0.475a
0.080b
CHAPTER III
EFFICACY OF VISUAL BARRIERS IN REDUCTION
OF BLACK-TAILED PRAIRIE DOG COLONY EXPANSION
Introduction
Once the most abundant mammalian herbivore of the American Great Plains
(Barko 1997, Wuerthner 1997), black-tailed prairie dogs (Cynomys ludovicianus) have
undergone a precipitous decline. Recent estimates suggest that just over 630,000 ha of
prairie dog occupied habitat, <2% of their historical range (Luce 2003), currently exists.
Factors contributing to the decline of prairie dogs include widespread government and
private eradication efforts (Roemer and Forrest 1996, Barko 1997), habitat loss due to
urban development and conversion of grassland to cropland, the spread of sylvatic plague
(Yersinia pestis), and unregulated hunting (Wuerthner 1997, Van Putten and Miller
1999). Due to the drastic decline of prairie dogs, persistence of threats, lack of protective
measures for extant populations, and the importance of prairie dogs in grassland
ecosystems, the National Wildlife Federation petitioned the US Fish and Wildlife Service
to list black-tailed prairie dogs as threatened throughout their range, as discussed in Van
Putten and Miller (1999). Listing was found to be warranted, but was precluded by other,
higher priority issues (Gober 2000), leaving black-tailed prairie dogs listed as a candidate
species (U.S. Fish and Wildlife Service 2002).
Zinn and Andelt (1999) conducted a survey of 87 people living near prairie dog
colonies and a random sample of 559 people in the Fort Collins, Colorado, USA area.
Those living near colonies held more negative views about prairie dogs than the general
40
population, and favored poisoning as a prairie dog removal technique. Conversely, the
general population favored capture and relocation. If black-tailed prairie dogs were to be
listed as threatened or endangered in the future, lethal control techniques (including
poisoning with treated baits or burrow fumigants; Hygnstrom and Virchow 1994), would
be prohibited. Poisoning may not always be socially acceptable or legal, emphasizing the
need for effective non-lethal prairie dog management techniques.
Non-lethal techniques currently available for prairie dog management include
deferred cattle grazing (Snell and Hlavachick 1980, Uresk et al. 1982), a temporary
chemosterilant (Garrett and Franklin 1983), live capture for subsequent relocation (Truett
et al. 2001), and visual barriers (Franklin and Garrett 1989). Of these, visual barriers
may have the greatest potential for use in the shortgrass prairie. Hygnstrom and Virchow
(1994) suggest that rotational or deferred grazing practices may have little effect on
prairie dogs in semiarid or shortgrass prairie regions, though this has not been tested.
Garrett and Franklin (1983) found diethylstilbestrol (DES), a temporarily chemosterilant,
to be effective in curtailing reproductive capability in prairie dogs in a small, controlled
study. However, they warned that use of this technique should remain probationary until
it has been tested for effectiveness on a larger scale. Additionally, DES must be handled
with extreme care (Franklin and Garrett 1989). Capture and relocation is extremely
labor-, time-, and cost-intensive (Hygnstrom and Virchow 1994), and often results in low
survival of translocated animals (Truett et al. 2001).
Use of visual barriers is based on the premise that prairie dogs prefer a visually
unobstructed environment to facilitate visual contact and communication between coterie
members, as well as to aid in detection of predators (Hoogland 1979). The importance of
41
an unobstructed view is evidenced by the tendency of prairie dogs to clip visually
interfering vegetation, even if it is not subsequently consumed (Koford 1958, Hoogland
1995). Use of visual barriers involves placing a barrier on the side of a prairie dog town
from which colony expansion is hoped to be diverted. This barrier blocks the view of the
colony residents, and discourages colony expansion in that direction beyond the barrier.
Visual barriers were first shown to be effective in reducing prairie dog site use
and colony expansion in South Dakota by Franklin and Garrett (1989). They stressed
that barriers constructed with burlap did not create a physical obstruction, implying that
the observed effect was due strictly to the visual obstruction. Since then, barriers have
become a standard recommendation for prairie dog management (Hygnstrom and
Virchow 1994), though the efficacy of the method has received little testing. Hygnstrom
(1996) evaluated the technique using snow fencing and found it to be ineffectual.
However, at 60% porosity, this material would be insufficient in creation of a visual
barrier.
Materials used as visual barriers have included burlap attached to steel stakes, 1-2
m high ponderosa pine trees (Franklin and Garrett 1989), and snow fencing (Hygnstrom
1996). Franklin and Garrett (1989) cautioned that barriers required almost daily repairs.
Damage incurred was due to rubbing by elk (Cervus elaphus) and bison (Bison bison).
They further cautioned that if this technique were applied on rangeland, domestic
livestock may cause similar damage (Franklin and Garrett 1989). Similarly, the first of 2
types of snow fencing used by Hygnstrom (1996) was damaged by wind and removed;
the second persisted with some maintenance.
42
Hygnstrom and Virchow (1994) assert that visual barriers have little utility due to
the comparatively high cost of construction and maintenance. However, if a material was
effective as a visual barrier and durable enough to be used multiple seasons with little
maintenance, the benefits may outweigh the initial cost. This study was conducted to:
(1) assess the efficacy of visual barriers in reducing prairie dog colony expansion; and (2)
assess the utility and durability of silt fencing and galvanized roofing as materials for
construction of visual barriers.
Methods
Visual barriers were constructed on 2 large prairie dog colonies at Melrose
Bombing and Gunnery Range (the Range), a 24,057-ha military installation in the
shortgrass prairie region of east-central New Mexico. The Range is characterized by a
semiarid climate, flat topography, and scattered, low shrubs, especially mesquite
(Prosopis spp.), and cholla and prickly pear cactus (Opuntia spp.). Colony 1 was
occupied by livestock and encompassed 111 ha at the time of barrier construction,
Colony 2 was ungrazed and 155 ha.
Three experimental sites were established at each prairie dog colony. One
treatment of galvanized roofing, silt fencing, and a control (no barrier) was randomly
assigned to each experimental site so that each colony contained a full complement of
treatments. Experimental sites were established and barriers constructed in late April
2002, before emergence of juvenile prairie dogs (as recommended by Franklin and
Garrett 1989) and subsequent colony expansion (Garrett 1982). Experimental sites were
separated by at least 200 m (Franklin and Garrett 1989).
43
Each barrier consisted of 2 parallel, 100 m rows of panels erected 3 m apart
(Figure 3.1). Panels were 6.1 m long by 1 m high, and were separated by 1.5 m breaks to
allow livestock to move freely between them. Rows were constructed so that the
midpoint of a break in one row corresponded with the midpoint of a panel in the next row
(Figure 3.1). This provided a 2.3-m panel overlap on both sides of an opening in any
row, thus creating an effective visual barrier without creating a physical barrier. Panels
were placed with their bases flush with the ground. Galvanized roofing panels were
painted gray to avoid image reflection (Robinette 1992).
Galvanized roofing panels were fastened to metal T posts with plastic zip ties or
metal wire. Silt fencing is manufactured in 30 m rolls with wooden stakes attached every
3 m. Additional staples were added to reinforce the silt fencing against high spring winds
that are characteristic of the region. To further fortify silt fence panels against the wind,
each panel was reinforced midway between the wooden support stakes with 2 pieces of
rebar, one on each side of the panel and attached at the top with wire or a plastic zip-tie.
Necessary repairs were made to barriers 2-4 times per month, with the exception
of the first month, during which no repairs were made. Repairs included patching holes
in silt fencing with duct tape, replacement of whole or half panels, and reinforcement of
wooden support stakes with rebar in the event of breakage. Due to the relative
infrequency of visits to the study site to make repairs to the barriers and the amount of
damage often sustained between visits, barriers constructed with silt fencing provided a
complete visual obstruction only intermittently throughout the season.
At each experimental site, total prairie dog burrows (excluding burrows that were
plugged or caved in) were counted on a 100 X 50 m plot external to the colony, bordering
44
the outer row of the visual barriers (Figure 3.1). Plot location was spatially similar
among treatments with respect to colony edge; all plots were permanently marked with
rebar. Burrows were located by walking 12.5 X 100 m transects within each plot, during
which each burrow was marked with a flagged metal stake. Subsequently, each plot was
traversed a second time to pick up stakes and search for any missed burrows. Counts
were conducted prior to visual barrier construction and at 4, 6, 8, 10, 12, and 14 weeks
post-barrier implementation.
Comparison of mean number of burrows was made between treatments using a
two-way ANOVA for the pre-treatment (26 April) count. To remove the influence of the
difference in initial number of burrows at each plot, similar comparisons were made for
subsequent dates/counts with ANCOVA, using the pre-treatment count as the covariate.
A conclusion that visual barriers had hindered colony expansion into adjacent,
uncolonized prairie would require that the number of total burrows for the control would
exceed that of galvanized roofing or silt fencing. All tests used an alpha level of 0.05 and
were performed using SAS software, version 8.2 (SAS Institute, Inc., Cary, North
Carolina, USA). Unequal means were separated using a protected least significant
difference (LSD) test.
Results
Four hundred m of barriers required 82 person-hours, or 20.5 person-hours per
100 m, to construct. A single 6.1 m galvanized roofing panel cost approximately $29,
translating to $4.75/m (not taking into account the cost of t-posts necessary for support).
In contrast, silt fencing cost approximately $1.30/m. No difference in mean number of
45
burrows was detected among treatments prior to barrier construction. Though the
number of burrows generally increased for all treatments, the galvanized roofing plots
experienced a slight decrease in the adjusted mean number of burrows from the first to
the second post-barrier construction counts, and increased by only 0.23 burrows from the
second to the third count (Figure 3.2). Concurrently, the number of burrows for both
other treatments increased, resulting in a differing number of burrows between
galvanized roofing and both silt fencing (t = -18.58; df = 1; P = 0.034) and control (t = 19.32; df = 1; P = 0.033) treatments on the third count. However, counts made ≥10
weeks post barrier construction did not differ among treatments.
There was a considerable difference in durability between the two materials used
to construct visual barriers. Barriers constructed with galvanized roofing sustained
damage sufficient to require repairs (replacement of broken zip-ties) on only 2 occasions
throughout the duration of the study. Conversely, the silt fencing required multiple (and
generally more substantial) repairs on almost every visit. The majority of damage was
caused by cattle, which broke the wooden support stakes and trampled the silt fencing.
This was further evidenced by the fact that the silt fencing barrier at the grazed colony
needed considerably more repairs than the silt fencing at the ungrazed colony, though the
number of repairs made was not quantified.
Discussion
Our results indicate that the presence of visual barriers did not hinder prairie dog
colony expansion. Though differences in number of adjusted mean burrows were
detected for the third post-barrier construction count, we believe that the lack of
46
significant differences in subsequent counts indicate that this difference was of no import.
Gaps in the barriers clearly did not deter cattle-induced damage. One possible measure
for reducing ungulate-caused damage to barriers would be to attach them to existing
fences. This could also potentially reduce cost by eliminating the need to purchase
support structures (for those materials which require such structures).
These results conflict with Franklin and Garrett’s (1989), and suggest that further
study is needed to determine the conditions and methods for which barriers are effective.
Future research should focus on: (1) spatial placement of barriers with respect to colony
edge; (2) multiple rows of barriers; (3) extension of barriers beyond the colony edge; and
(4) burying the base of the barriers (thus assuring that no light will show at the bottom
and providing some degree of a physical barrier). A longer-term study would be
beneficial to determine if barriers are effective in the same location over multiple seasons
or need to be moved periodically.
Galvanized roofing would be a suitable material for use in future study of visual
barriers due to its durability and low maintenance requirement. However, galvanized
roofing is somewhat expensive. Hygnstrom (1996) reported that the snow fencing he
used cost about $1.80/m. Franklin and Garrett (1989) did not report material costs, but
the burlap and road-cleared ponderosa pines (Pinus ponderosa) they used would be less
expensive. For purposes of future research, silt fencing may be adequate for use in some
situations (i.e., no ungulates present or when barriers are attached to existing fences,
preventing ungulate damage). However, for long-term use or in situations where it is not
possible to make necessary repairs, galvanized roofing may be a more sensible material.
47
Literature Cited
Barko, V. A. 1997. History of policies concerning the black-tailed prairie dog: a review.
Proceedings of the Oklahoma Academy of Science 77: 27-33.
Franklin, W. L., and M. G. Garrett. 1989. Nonlethal control of prairie dog colony
expansion with visual barriers. Wildlife Society Bulletin 17: 426-430.
Garrett, M. G. 1982. Dispersal of black-tailed prairie dogs (Cynomys ludovicianus) in
Wind Cave National Park, South Dakota. Thesis, Iowa State University, Ames, Iowa,
USA.
Garrett, M. G., and W. L. Franklin. 1983. Diethylstilbestrol as a temporary
chemosterilant to control black-tailed prairie dog populations. Journal of Range
Management 36: 753-756.
Gober, P. 2000. Endangered and threatened wildlife and plants; 12-month finding for a
petition to list the black-tailed prairie dog as threatened. Federal register 65: 54765488.
Hoogland, J. L. 1979. The effect of colony size on individual alertness of prairie dogs
(Sciuridae: Cynomys spp.). Animal Behaviour 27: 394-407.
Hoogland, J. L. 1995. The black-tailed prairie dog: social life of a burrowing mammal.
University of Chicago Press, Chicago, Illinois, USA.
Hygnstrom, S. E. 1996. Plastic visual barriers were ineffective at reducing
recolonization rates of prairie dogs. Pages 74-76 in R. E. Masters, and J. G.
Huggins, editors. Proceedings of the Twelfth Great Plains Wildlife Damage Control
Workshop.
Hygnstrom, S. E., and D. R. Virchow. 1994. Prairie dogs. Pages 85-96 in S.
Hygnstrom, R. Timm, and G. Larson, editors. Prevention and Control of Wildlife
Damage. U.S. Department of Agriculture, Lincoln, Nebraska, USA.
Koford, C. B. 1958. Prairie dogs, whitefaces, and blue grama. Wildlife Monographs: 3.
Luce, R. J. 2003. A multi-state conservation plan for the black-tailed prairie dog,
Cynomys ludovicianus, in the United States – an addendum to the black-tailed prairie
dog conservation assessment and strategy, November 3, 1999.
Robinette, K. W. 1992. Black-tailed prairie dog management: translocation and barriers.
Thesis, Colorado State University, Fort Collins, Colorado, USA.
48
Roemer, D. M., and S. C. Forrest. 1996. Prairie dog poisoning in northern Great Plains:
an analysis of programs and policies. Environmental Management: 20: 349-359.
Snell, G. P., and B. D. Hlavachick. 1980. Control of prairie dogs – the easy way.
Rangelands 2: 239-240.
Truett, J. C., J. L. D. Dullum, M. R. Matchett, E. Owens, and D. Seery. 2001.
Translocating prairie dogs: a review. Wildlife Society Bulletin 29: 863-872.
Uresk, D. W., J. G. MacCracken, and A. J. Bjugstad. 1982. Prairie dog density and
cattle grazing relationships. Pages 199-201 in R. M. Timm, and R. J. Johnson,
editors. Proceedings of the Fifth Great Plains Wildlife Damage Control Workshop.
Lincoln, Nebraska, USA.
U.S. Fish and Wildlife Service. 2002. Endangered and Threatened Wildlife and Plants.
Federal register 67: 40657-40679.
Van Putten, M., and S. D. Miller. 1999. Prairie dogs: the case for listing. Wildlife
Society Bulletin 27: 1110-1120.
Wuerthner, G. 1997. Viewpoint: the black-tailed prairie dog – headed for extinction?
Journal of Range Management 50: 459-466.
Zinn, H. C., and W. F. Andelt. 1999. Attitudes of Fort Collins, Colorado residents
toward prairie dogs. Wildlife Society Bulletin 27: 1098-1106.
49
Figure 3.1. Spatial arrangement of experiment addressing efficacy of visual barriers in
reduction of prairie dog colony expansion at Melrose Bombing and Gunnery Range,
Roosevelt County, New Mexico, summer 2002. Closed circles indicate prairie dog
burrows. Visual barriers were constructed with either silt fencing or galvanized roofing
panels, each was replicated twice.
50
Adjusted Mean Burrows
40
35
Galvanized Roofing
Silt Fencing
Control
30
25
20
15
10
5
0
4/26
5/10
5/24
6/7
6/21
7/5
7/19
Date
Figure 3.2. Burrows (adjusted for number at initial count) detected by survey date for
each treatment of galvanized roofing, silt fencing and control at prairie dog colonies at
Melrose Bombing and Gunnery Range, Roosevelt County, New Mexico, summer 2002.
51