United States Department of Agriculture, Forest Service
Pacific Southwest Research Station
Sierra Nevada Research Center
Links between landscape condition and survival and reproduction of
fishers in the Kings River Area in the Sierra National Forest
Fishers and fire in the Sierra Nevada Mountains
Historically, the Sierra Nevadas were characterized by frequent, low-intensity surface fires
that reduced fuel loads and created a mosaic of wildlife habitat. However in the interests
of protecting developments or natural resources, 20th century forest management was
dominated by fire suppression efforts and a gradual buildup of fuels. Now, the regional
fire regime has changed; fires are larger, more intense, and outside the range of historic
variability. Faced with this fact, forest managers are now searching for ways to reduce fuel
loads and bring the fire regime back within historical bounds without harming native
species.
In particular, there is great concern that fuel reduction efforts will harm the small, native
fisher population in the southern Sierras. Isolated, reduced to less than 400 individuals,
and genetically homogeneous, the population is considered to be at high risk of extinction.
In 2004 the U.S. Fish and Wildlife Service found that protection for the west coast
population of fishers was warranted, and CA Department of Game and Fish is currently
considering a petition to list the species as state endangered.
Fishers’ preference for dense, structurally-diverse forests present a conservation challenge;
how to balance the short-term risks associated with forest thinning and fuel reduction
with the larger risk of a habitat-destroying catastrophic fire? Recently, the Conservation
Biology Institute released a comprehensive modeling effort designed to help clarify this
balance. Their conclusion was that the risk and negative impacts of a catastrophic fire
overshadowed any loss of habitat associated with fuel reduction efforts. Despite this clear
recommendation, managers are still faced with the daunting task of deciding how to
implement fuel reduction efforts in such a way that any negative impacts on fishers and
other closed canopy species are minimized.
Project Overview
In response to the challenges outlined above, in 2006 the Kings River fisher study was
initiated jointly by U.S. Forest Service Region 5 and the USFS Pacific Southwest Research
Station for two reasons: 1) to fill gaps in our current understanding of fisher ecology and
habitat requirements and 2) to address the uncertainty surrounding the effects of timber
harvest and fuels treatments on select response variables of interest, including fishers and
their habitat. Specific question include:
► What are the responses of fishers to changes in forest structure and composition?
► Are there thresholds in forest and landscape structure beyond which
habitat becomes unsuitable or reproduction declines?
► Do changes in habitat quality translate into changes in fisher population
vital rates by altering factors such as den site availability, exposure to
predation risk, or physiological stress?
► How do fishers respond to changes that are primarily a result of fuels
treatments, and at what spatial scales?
METHODS
Study Design
The Kings River fisher project is designed around two central ideas. First, using multiple, complementary research
techniques will overcome many of the limitations faced by previous studies. Second, the Kings River Project
presents a rare and unprecedented opportunity to monitor the impacts of large-scale forest management activities on
fisher using a before-after/control-impact (BACI) framework. This means that population, behavior, and
physiological data is collected in both control and treatment areas, and the effects of management activities can be
identified. For example, density is often used as an index of population stability. In the Kings River area, fisher
density will be evaluated using a combination of genetic mark/recapture, radio telemetry, and remote camera data.
Any changes in density following treatments will be used to evaluate the effects of management activities. A similar
approach is being used for other aspects of fisher ecology such as survival, reproduction, and habitat use.
LiveLive-trapping – Tomahawk box traps, equipped with an attached cubby for the animal’s
comfort and security, are placed in alternating 1km² grid cells. Traps are checked every
morning and closed when severe weather events are expected. Captured animals are
anesthetized, weighed, sexed, aged, and equipped with radio collars.
Biological sampling – Biological samples collected during captures include tissue, blood,
and hair samples as well as bioelectrical impedance (BIA). Tissue and hair samples are used
for DNA analysis, allowing us to identify parental and sibling relationships as well as link
individual animals to samples collected by scat detector dogs. Blood samples are used to
evaluate past and current exposure rates to pathogens such as canine distemper and
parvovirus. BIA measurements are a non-lethal way to calculate body fat, and changes in
scores can reflect changes in body condition related to fuel treatments.
Radio Telemetry – A combination of auditory mortality checks, remote
triangulations, rest-site walk-ins, movement path, and aerial telemetry is being
employed to monitor fisher survival, behavior, and habitat use. Experimental GPS
collars are planned for use in Fall ‘08.
Scat Detector Dog Surveys – Detector dog teams, provided by the University of
Washington’s Center for Conservation Biology, conduct fall and spring surveys of the
study area. Scats are confirmed as fisher using genetic analysis, then sent on to the USFS
RMRS Wildlife Genetics Lab for individual identification. Additional information includes
habitat characteristics surrounding collection site, prey remains, and hormone levels.
Remote Camera Surveys – Remote cameras will be used quantify the activity
levels of different carnivore species in control and treatment areas. They also allow
us to non-invasively count the number of kits surviving to independence.
PRELIMINARY RESULTS
2007 / 2008 Research Highlights
► Capture success: 28 animals captured between 1 Feb 07 and 15 July 08 [15 female (13 adult, 2 subadult), 13
male (5 adult, 6 subadult)].
► Historic recaptures: Of all adult captures, 89% of females and 20% of males were originally captured by either
Amie Mazzoni or Mark Jordan between 1999 and 2004.
► Survival: 8 animals have died (5 male, 3 female): 1 bobcat predation, 1 coyote predation, 1 unconfirmed lion
predation, 2 unknown predation, 1 drowning, 1 hit by car, 1 accidental entombment. 1 additional animal (male)
is a suspected predation-related mortality, but the carcass is currently unrecoverable.
► Reproduction: 64% of adult females showed evidence of nursing during summer, 2007.
89% of adult females raised kits during summer, 2008.
Females averaged at least 1.5 kits per litter in 2008 (9 kits in 6 litters counted)
► Denning habitat: 7 natal and 6 maternal dens located in 2008. These are the first fisher dens found on the
Sierra National Forest.
► Scat Dog Surveys: Fall ‘06, Spring ‘07, and Fall ‘07 data have been analyzed. Overall the dogs were 60%
accurate, resulting in 351 confirmed fisher scats being collected. These samples are currently being processed
Distribution of study animals with the
study area. M indicates males, F
indicates females. Ellipses represent
approximate areas used, not actual
home ranges. Den sites are
approximate. Green indicates the eight
management unit proposed for fuels
treatment under the current Kings
River Project.
Epidemiology: Serology tests show past exposure to parvovirus, canine adenovirus, and toxoplasmosis but not
canine distemper. Additional tests planned include exposure to canine herpesvirs, West Nile virus, plague, Rocky
Mountain spotted fever, leptospirosis, heartworm, and Lyme disease. (Mourad Gabriel, IERC, unpublished data)
Pathogen
Past Exposure (Serology)
Current Infection (PCR)
Canine Distemper Virus
Parvovirus
Canine Adenovirus
Anaplasma phagocytophilum
Toxoplasmosis
Completed (0 of 19 – 0% positive)
Completed (8 of 19 – 42% positive)
Completed (3 of 19 – 16% positive)
Completed (1 of 10 – 10% positive)
Completed (0 of 19 – 0% positive)
Completed (2 of 19 – 11% positive)
PRELIMINARY RESULTS—REST AND DEN STRUCTURES
Denning and resting habitat: Kings River fishers use a variety of species and structures. Dens have been found
in black oaks, incense cedars, ponderosa pines, sugar pines, and white firs. 71% of dens were in live trees, but all had
some degree of decadence and DBH ranged from 69 to 165 cm (27 to 65 in). Rest sites are more variable and have
included live and dead trees of many species, cavities, platforms, stick nests, stumps, and logs.
Live white fir
with dead top.
(natal den)
3 month old
kit napping at
the entrance
of a maternal
den in a large
incense cedar
snag.
Black oak
snag.
(natal den)
Live incense
cedar.
(rest site)
Live Jeffery
pine.
(rest site)
Live sugar
pine.
(rest site)
Incense cedar
snag.
(rest site)
Female fisher
resting in a
stick nest
located in a
ponderosa
pine.
Live ponderosa pine with
lightening
scar. (den)
Live black oak
w/ basal
hollow.
(natal den)
COLLABORATORS
For additional information, contact:
Dr. Craig Thompson, Research Wildlife Ecologist
cthompson@fs.fed.us
(559) 760-9995
Dr. Kathryn Purcell, Research Wildlife Biologist
kpurcell@fs.fed.us
(559) 868-6233
Dr. Peter Stine, SNRC Program Director
Kings River Fisher Project study area within the Sierra
National Forest. The Kings River Administrative Area
is outlined in red. The appropriate elevation range for
fisher is shown in green.
SIERRA FISHER FACT SHEET—MARTES PENNANTI
Common name: Fisher
Species: M. pennanti
Genus: Martes
Family: Mustelidae
Order: Carnivora
Average weight
Males: 3.7 kg
Female: 2.1 kg
Description
Fishers are mid-sized carnivores, weighing between 2 and 7 kg (4-15 lbs). They are
sexually dimorphic, with males often being twice as large as females. They are arboreal
carnivores, meaning they move easily and hunt throughout the forest canopy. All four
feet have five toes with retractable claws, and because they can rotate their hind paws
180 degrees, they can easily grasp limbs and run down trees head first.
Habitat preferences
Gestation period
11-12 mo (delayed
implantation)
Being arboreal, fishers prefer areas of dense overhead
cover and structural diversity. They avoid open spaces,
yet can be found in shrub or regenerating stands
where sufficient biomass and cover are present.
Zielinski et al. (2004) found that fisher rest sites were
strongly correlated with dense canopies, large trees,
and steep slopes. In the Sierra Nevadas, they are
limited to an elevation range of approximately 3000 to
7500 feet (915-2286m), presumably due to a Fisher, a member of the weasel
family, are also known as Americombination of temperature and snow depth.
Number of kits per
litter: 1-4, average 1.5
Reproductive Ecology
Primary prey
Scurids
Lagomorphs
Insects
Fungi
Reptiles
Birds
Berries
Carrion
Breeding season: April
Habitat associations
Dense canopy cover
Steep slopes
Large trees
Sources of mortality
Intraguild predation
‘Accidents’
can sables or fisher cats.
In the southern Sierra Nevada, 1 to 3 kits are born
mid to late April. Prior to giving birth, females
carefully select a ‘natal’ den based on a number of
characteristics including cavity size, entrance size, and
solar exposure. Females will remain in the natal den
for 1-4 weeks before beginning to move kits to a
series of ‘maternal’ dens. By mid July kits are capable
of following the females while they hunt, and by late
August some may begin dispersing.
Fishers, with rotating hind claws,
are as comfortable in the trees as
Distribution and conservation status
they are on the ground and often
Fishers are found across central Canada, from New England down into the leap between trees.
Appalachians, around the Great Lakes, down into the Rocky Mountains, and again
down the Cascade and Sierra Nevada ranges into California. Once widespread, fisher
populations were decimated in the late 1800s and early 1900s due to fur trapping and
other habitat changes (Krohn et al. 1997). Current populations in the Rocky
Mountains, Oregon, and Washington are the result of translocations (Drew et al.
2003).
In 1937, Grinnell described the distribution of fishers in California as a continuous
arc from the Coast Range eastward to the southern Cascades, then south throughout
the Sierra Nevada. By 1942 the fisher was described as “near extinction in
California” (Hall 1942), and trapping was banned in 1946. Despite this reprieve,
fisher numbers continued to decline throughout the latter half of the twentieth
century. By 1987, Gould (1987) concluded that fishers had disappeared in the
northern Sierras. Today, a small native population of fishers persists in the southern Female fishers frequently move
their kits between dens. This one
Sierras, separated from the nearest source population by 400 km.
is carrying a kit down a tree by
Particularly vulnerable due to extreme population fragmentation and habitat loss the holding it’s head in her mouth.
West Coast fishers are considered a “species of special concern” by the California
Department of Fish and Game (CaDFG) and a “sensitive species” by the U.S. Forest Service. In 2004 the U.S. Fish
and Wildlife Service ruled that listing this population under the Endangered Species Act was “warranted but
precluded” (USDI 2004) and CaDFG is currently considering a petition to list the species as state endangered.