USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
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Research Topics Wildlife & Fish

Kings River Fisher Project
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Kings River Fisher Project

Fisher (Pekania pennanti) ecology in the southern Sierra Nevada – interpreting habitat use in a landscape altered by tree mortality

A male fisher in decayed old conifer snag.
Male fisher (M71) in a decayed old conifer snag. (E. Paton)

The Kings River Fisher Project (KRFP) was initiated in 2007 by PSW to gather baseline data on fisher ecology and to learn more about aspects of fisher habitat used to inform forest management in the southern Sierra Nevada (SSN). Fishers in this southernmost portion of their range are of special conservation concern due in part to low numbers and isolation from other populations. Their close ties to features of mature forest also make them a species of interest for the USFS.

PSW designed the research program to incorporate a variety of methods including radio telemetry to identify reproductive dens and locate carcasses of fishers that died in the field to determine causes of mortality. Researchers also included a non-invasive method to look at occupancy of areas over time – scat detector dog surveys to locate fisher scat in the forest.

Although KRFP staff are currently still summarizing and analyzing data from this project, quite a few products associated with the initial years of this project are currently available – including information on fisher reproductive ecology, characteristics of structures used for resting and denning, causes of mortality, and impacts of rodenticides.

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Dead trees with a fisher in a circle to demonstrate fisher habitat.
Example of an area occupied by fishers that has been impacted by tree mortality. Note that many of the conifers have died but the oaks are still alive.
New Focus on Tree Mortality

Beginning in 2012 and continuing into 2015, California experienced a period of extremely low precipitation paired with high temperatures. This extreme drought led to trees becoming water-stressed and vulnerable to bark beetles. In the years following the drought, extensive outbreaks of beetles in the southern Sierra Nevada led to wide-spread tree mortality – particularly of conifers such as Ponderosa pine, sugar pine, and white fir.

As areas with some of the highest tree mortality overlap with the habitat types and elevations commonly used by fishers on the west slope of the Sierra Nevada, funding was provided by Region 5 (USFS) to continue gathering data to better understand fisher use of this altered landscape. In fall 2017, the project transitioned to collect fine scale location data using small GPS collars. In collaboration with Oregon State University, we began creating detailed tree mortality maps for use in spatial analysis that can inform both forest management and fisher conservation in this region.

Study Area

The KRFP study area is on the High Sierra District of the Sierra National Forest near Shaver Lake, California.

A male fisher in decayed old conifer snag.
Photo guide with examples of the types of structures and microsites used by fishers for resting and denning.
[Download, 5.6 MB]

Here are a few highlights from field work and research topics we are currently working on.

Tree mortality mapping: Two products related to tree mortality: 1) a land cover classification map for the KRFP study area, and 2) a fractional cover map which includes much of the southern Sierra Nevada. For the land cover map, supervised land cover classification techniques are used to map five land cover categories, including tree mortality, at a 5-meter pixel resolution. Researchers are building on the categorical land cover product to develop a model of fractional cover (i.e., the proportion of each land cover type) across a broader area at a 30-meter pixel resolution. These products will include a raster layer each year (2014-2018).

Captures: Between 2007 – 2020, we have captured more than 170 individual fishers. In addition to attaching VHF collars in the early years, and focusing on GPS collars in the later years, we also collected samples (e.g., blood, hair, tissue, swabs) for use in collaborations: test for disease (IERC), confirm genetic identity (RMRS), evaluate diet using isotopes (Univ. of WI), and assess hormone levels (Utah State). In winter 2020, the last new female we captured, processed and released without a collar was F106.

Den location and monitoring: Between 2007 – 2019, we located reproductive dens of female fishers in spring to gather baseline data on reproductive ecology in this region and identify the types of structures (generally large trees with hollows) used as dens. In 2018, we collaborated with the USFS Region 5 Carnivore Monitoring Program to evaluate the detectability of reproductive females at cameras during the den season and develop a survey protocol for use by management. In spring 2019 (our last den survey season), we documented a female (F87) at her den on the day she moved her kit.

Characterizing patterns of fisher movement using GPS collar data: Between October 2018 and March 2020, we programmed GPS collars to collect a subset of data at frequent intervals (15-min) for 5-day bursts to understand how fishers are moving in a landscape altered by tree mortality and associated management. One of our goals was to gather data that can identify characteristics of linkage habitat as well as potential barriers to movement in order to inform landscape planning. We will be working with Mississippi State University to quantify movements relative to habitat availability in conjunction with the tree mortality spatial data.

Assessing change in fisher occupancy and diet using scat detector dogs: From 2007 – 2018, we worked with Conservation Canines (University of Washington) to perform detector dog surveys to find fisher scats. We are now using this long-term data set to conduct two interesting pre- and post-tree mortality analyses. First, we are collaborating with Oregon State University to look at occupancy over time relative to tree mortality. Second, we are working with Rocky Mountain Research Station and the University of Montana to assess changes in diet using metabarcoding techniques.