# HABITAT USE, BEHAVIOR, AND LIMITING FACTORS AFFECTING THE PYGMY RABBIT (*Brachylagus idahoensis*) IN GRASS VALLEY, UTAH

By Principle Investigators:

*Jerran T. Flinders, PhD,* Professor, Wildlands and Wildlife Ecology,
Brigham Young

University, 407 Widtsoe Building, Provo, UT 84602,
jerran_flinders@byu.edu

*Jackee L. Alston, M.S.,* Research Associate, Wildlands and Wildlife
Ecology, Brigham

> Young University, 9330 N Valerie Way, Flagstaff, AZ 86004,
>
> jackeealston@yahoo.com

*Randy T. Larsen*, Research Associate, Wildlands and Wildlife Ecology,
Brigham

Young University, 401 Widtsoe Building, Provo, UT 84602,
rtl5@email.byu.edu

**ABSTRACT:**

Impaired sagebrush ecosystems are a dilemma facing managers across the
Western US. These ecotypes are being treated to either (a) create
alternate habitats for species such as Sage‑grouse, elk and mule deer,
(b) increase livestock forage production, or (c) reduce fire fuels by
replacing sagebrush with grasses. Current data are incomplete on the
impacts of these treatments on state sensitive species and federally
petitioned species, and in particular the pygmy rabbit. In Grass Valley,
Utah, well-meaning treatments of sagebrush habitat include: federally
funded wildfire fuel reduction operations; sagebrush canopy reductions;
and combinations of objectives that remove most or all of the sagebrush
canopy and replace them with grasses, forbs and even shrubs favored by
mule deer, elk, domestic sheep and domestic cattle. The objective of
this study was to determine if such activities were impacting pygmy
rabbits and to elucidate habitat use, occurrence and abundance of the
pygmy rabbit.

Pygmy rabbit abundance in Grass Valley was found comparable to estimates
found in Idaho (0.79 rabbits/ha; 0.54 rabbits/ha respectively). These
values likely represent a lower abundance estimate than historical
values, though both areas probably represent the highest abundances in
their respective state. Pygmy rabbits in Grass Valley, Utah were found
to select areas for burrow sites that comprised taller, more decadent,
and larger canopied shrubs than surrounding habitat or comparable,
random habitat. Occupied and unoccupied habitat locations had shrubs
similar in height and decadence; however shrub canopy area was
significantly larger in occupied habitat. Shrub spatial pattern was more
uniform (i.e. more open) in unoccupied random sites than in occupied
sites where habitat was more clumped in dispersion pattern.

Big sagebrush was comprised one third to almost half of the understory
found at burrow sites while in random, unoccupied habitat understory
consisted of much less a proportion. Instead, grasses and forbs were
more abundant in random, unoccupied locations than in burrow system
locations. This suggests a lack of summer foraging species in occupied
pygmy rabbit habitat. In comparing big sagebrush density at burrow sites
to other shrubs, big sagebrush is much more abundant. Sagebrush was also
more abundant at burrow sites than at random, unoccupied sites. Big
rabbitbrush was more abundant on average at burrow sites than at random,
unoccupied sites, though not at the densities of big sagebrush. Pygmy
rabbits appear to utilize habitat based on predator avoidance and browse
forage needs.

Burrows were more commonly only one opening and burrows with two or more
openings comprised 50.8% of the burrows observed. Single opening burrows
were more commonly associated with a nearest neighbor burrow with
multiple openings. Distance was correlated with whether burrows were one
opening or multiple openings. Burrows with one opening are more likely
to be closer together when the nearest neighbor is a single opening as
well. Burrows were farther apart when a multiple entry burrow was
nearest another multiple entry. This correlation is likely a function of
predator escape and valuable in habitat where foraging home range is
larger than previously documented, as is likely in Grass Valley. This
study was established to be a multi-year project and conclusions drawn
from the results should take this into consideration. Data reported here
are inconclusive until more research can be added to this study.

**INTRODUCTION.**

Throughout the Intermountain West the pygmy rabbit (*Brachylagus
idahoensis*) has seen severe population declines (Flinders 1999; Janson
2002). These have primarily occurred due to anthropogenic threats and
the limited knowledge available to properly manage this specialized
lagomorph. The pygmy rabbit is an obligate sagebrush-steppe resident
that inhabits self-made or self-altered burrows in sagebrush habitats
(Green and Flinders 1980a and 1980b). This rabbit is the smallest
leporid in North America. The home range of an individual pygmy rabbit
consists of 30 km5 in relatively high sagebrush cover (21 - 36%) and
loose, alluvial soils (Green and Flinders 1980a; Green and Flinders
1980b; Weiss and Verts 1984; Katzner and Parker 1997; Flinders 1999). In
some areas, pygmy rabbit burrow sites may be circumscribed by a mounded
area with the tallest shrubs ranging from 53-75 cm in Wyoming big
sagebrush (*A. tridentata wyomingensis - -* White et al. 1982).
Sagebrush comprises 99% of a pygmy rabbit=s winter diet and 51% of their
summer diet (Green and Flinders 1980a; Green and Flinders 1980b; Gahr
1993). Summer diet also includes 39% grasses and 10% forbs (Green and
Flinders 1980a).

Due to the recent decline of pygmy rabbit population numbers and the
severe diminution and degradation of their habitat, a petition was filed
in 2003 to the United States Fish and Wildlife Service (USFWS - -
Western Watersheds 2003). This petition calls for the listing of the
pygmy rabbit as Threatened or Endangered under the Endangered Species
Act of 1973. Before this petition, other states had initiated efforts
for conservation. Throughout its range this species has been listed as a
state species of special concern (CA, ID, WY, MT, NV, and UT).
Washington populations are listed state and federally as an Endangered
Species (Federal Register 2003).

Current and past research has been directed at identifying pygmy rabbit
abundance, distribution, forage and habitat use, genetics, and dispersal
patterns (Green 1978; Green and Flinders 1981; Katzner et al. 1997;
Katzner and Parker 1997; Katzner and Harlow 1998; Heady et al. 2001;
Bartels and Hays, 2001; Siegel et al. 2002). However, no information yet
exists on the current limiting factors facing this petitioned species
and no data have been collected on pygmy rabbit populations in Utah
since the 1970\'s, excepting limited surveys (Janson 2002). In
particular, information does not exist on how many well-meaning habitat
improvement practices are affecting pygmy rabbit habitat use and
population densities.

This cooperative study was initiated to aid land and resource managers
with the data necessary to manage this petitioned species. Investigators
incited a four-fold, long-term approach to research. First, we attempted
to identify extant populations of pygmy rabbits on Bureau of Land
Management (BLM) land. Second, in selected areas in Grass Valley, Utah,
we examined habitat use and pygmy rabbit abundance. Third, we worked to
determine the limiting factors, if any, affecting pygmy rabbits in Grass
Valley, Utah. In particular, a potential limiting factor investigated
relates to sagebrush treatments instigated by land managers. Sagebrush
ecotypes are being treated to either (a) create functioning habitats for
species such as Sage‑grouse (*Centrocercus urophasianus*), Rocky
Mountain elk (*Cervus elaphus*), and mule deer (*Odocoileus hemionus*),
(b) increase livestock forage production, and/or (c) are involved in
fuels reduction programs. These objectives or combinations of objectives
remove most or the entire sagebrush canopy and replace the sagebrush
with grasses, forbs and exotic shrubs.

Current data are incomplete on the impacts of sagebrush treatments on
state sensitive species and federally petitioned species, forefront
among these is the pygmy rabbit. Such data require pre-treatment and
post-treatment monitoring at multiple scales and with multiple species.
Products from our long-term research are anticipated to aid managers
with knowledge of the habitat requirements utilized by pygmy rabbits,
limiting factors in its conservation, alternatives to recovery, and
identify the positive and negative effects of habitat manipulation.

**STUDY AREA.**

This study was conducted in south-central Utah in Grass Valley (Piute,
Sevier, and Wayne Counties). Grass Valley (hereafter known as the
Valley) is located between Monroe Mountain and the Awapa Plateau, just
southwest of the Fish Lake Mountain Range and immediately north of Otter
Creek Reservoir. Otter Creek itself runs the width of the Valley until
it reaches the reservoir. Koosharem, Sevier County and Greenwich, Piute
County are located in the center of the valley with a cumulative
population estimate of 276 (US Census 2000). The elevation of Koosharem
and Greenwich is approximately 2,113 m (6,930 ft) and annual, average
precipitation is 24.08 cm/year (WRCC 2005). Temperatures range from
29.3°C in the summer to -12.2°C in the winter. Outdoor, recreation
activities in pygmy rabbit habitat primarily include hiking, hunting,
and off-road vehicle (ORV) use. Grass Valley is commonly known for
access roads to the Piute Trail, a popular ORV trail. Other land uses
include several cattle and sheep grazing on private, BLM, and US Forest
Service (USFS) lands. Vegetation includes a relatively strict succession
of wet, grassy valley bottoms (mostly agricultural fields), big
sagebrush (*Artemisia tridentata tridentata*) foothills, juniper
(*Juniperus* spp.) and pinion pine (*Pinus edulis*) hillsides and spruce
(*Picea* spp.), fir (*Abies* spp.) and aspen (*Populus tremuloides*)
mountain tops. The research on this study, however, only focused on the
big sagebrush foothills, areas where pygmy rabbits were likely to occur.

**METHOD AND MATERIALS.**

***Occurrence, Distribution, and Abundance***

Walk transects were preformed in habitat suspected of pygmy rabbit
presence throughout Grass Valley and BLM lands. Two types of line
transects were used. First, transects of straight lengths of 250 m were
developed to assist with abundance estimates and give the best estimate
of true abundance possible. Second, transects of no set length were
walked in more imperfect line transects. Longer transects were used in
discontinuous pygmy rabbit habitat such as sagebrush removal sites or
patchy sagebrush sites and used to compare to pre-treatment surveys by
the BLM. All animals were recorded 15 m on each side of the line
transect, creating a 30 m survey strip. Where pygmy rabbit sign was
encountered a Global Position Unit (GPS) location was taken and data
such as the type of sign, if a burrow then the number of openings, the
activity level of the burrow, and the number of individual animals were
recorded. Burrow activity level is a scale defined by Rachlow and
Whitham (2004) with a "1" representing Active (known by open/intact
burrow entrance, fresh pellets, and fresh diggings); "2" representing
Recent (known by intact/open burrow entrance, old/weathered pellets, and
absent/old/few tracks); "3" describing Old (intact/open/debris present
burrow entrance, pellets absent, diggings absent/old/few; and "4"
recorded for Very Old (burrow collapsed, pellets absent, diggings
absent/old/few). ARCGIS (ESRI 2004) software was used to view pygmy
rabbit distribution based on the walk transect data and to map active
and inactive burrows in Grass Valley.

Trailmaster (TM1550) digital track cameras (i.e. remote cameras)
assisted in looking at burrow use, verify activity levels, study pygmy
rabbit behavior, and identify timing of rabbit movements outside the
burrow. An active or recently active burrow system was chosen at random
and a camera was set up approximately 1 m from a burrow opening. These
cameras were set to take a picture every 30 seconds when a rabbit
crossed the infrared trigger beam. Cameras were kept on the burrow
opening for two weeks and then moved to another site.

Walk transects also assisted in determining abundance of pygmy rabbits
in Grass Valley. Within the 30 transect strip, all wildlife were
identified and the distances from the transect line recorded. Distances
from burrow systems were analyzed using the software DISTANCE 5.0 Beta 3
(released: January 6, 2005) to obtain crude density estimates. Model
selection in this software was preformed using Akaike's Information
Criterion (Buckland 1992; Akaike 1973).

***Habitat Use***

Habitat Use data were collected by two different means. First, shrub
data were collected on walk line transects and were assumed to be
associated with animals documented nearest the GPS location of the shrub
data. This assumption was based on using a GPS location to select the
shrub data taken nearest to where the animal was recorded. Second, more
intensive habitat data were collected on randomly selected burrows
encountered on transects. These latter data were collected at a
different time when the observer would return to the location and
identify a random burrow to perform more fine scale habitat
measurements. By both means Number range CHAPTERT-square shrub
dispersion analyses were conducted (Ludwig and Reynolds 1988). The
dispersion analyses estimated the density, pattern, and occurrence of
the 2 closest woody plants to the center of the burrow (i.e. nearest
neighbor). Other relevant data were collected simultaneously on each
shrub (i.e. species, degree of shrub decadence, shrub canopy area
calculated as an ellipse, and shrub height). Decadence is defined here
as the proportion of the plant yellowed, dead, or dying and is an ocular
estimate. Statistics used in habitat assessments are by and large
descriptive, as this is only one year of research and more definitive
conclusions from sophisticated statistics could be misleading.

Fine scale habitat measurements were taken at randomly selected burrow
sites encountered on a line transect. These areas were returned to using
a GPS location after the walk transects had been completed. Habitat was
only collected on burrows that were categorized as active or recently
active. At these sites, a center location was identified by averaging
the distance between all openings in the system and choosing this
average as the middle for habitat data collection. If a system was a
single entrance burrow, then the center of the opening was the center
point. Six main habitat data collection methods were used once the
center was identified; understory quadrat data, macrohabitat parameters
(measured as distances from the burrow system), T-square shrub
dispersion analysis (previously discussed), horizontal obscurity
estimates, all shrub density at burrow sites, and plant canopy cover
using line intercept. Data were collected similarly in randomly chosen
locations in unoccupied habitat for habitat selection comparisons.

Understory quadrat data were collected by laying a one-quarter m²
quadrat square at the center location of the burrow system and then
identifying plant species, bare ground, litter, moss, and bare rock
within the quadrat. Each category is estimated as a percentage of the
whole quadrat, giving the measurements a proportional density. Once the
center point is calculated, random locations were measured with the same
methods 0-15 m away in each cardinal direction. Macrohabitat was
measured by using a rangefinder to record distances of the nearest:
natural habitat edge, human caused edge (i.e. habitat treatment or
overgrazing site), human structure (i.e. buildings or telephone poles),
ORV tracks, big rabbitbrush (*Chrysothamnus viscidiflorus*) or
greasewood (*Atriplex confertifolia*), predator sign, ungulate sign,
pygmy rabbit pellet pile, cliff or rock outcropping, and raptor perch.
The type of human caused edge, human structure, and ORV tracks were also
identified and recorded categorically.

Horizontal cover is important as a function of predator avoidance for
many animals. Horizontal cover is defined as high vegetation or boulders
on flat terrain that limits an animal's view of their close surroundings
(Beck et al. 1996). Horizontal obscurity was measured using a 1 m² cover
board. The obscurity board was placed at the center point and counted
from each cardinal direction at 2.5 m, 5 m, and 10 m away from the
center. The board was counted by kneeling (i.e. terrestrial predator
height) and counted in 3 sections- bottom, middle, and top- each with 12
squares and totaling 36. The number of squares devoid of any visual
obstruction was recorded and set in proportion to the total number of
squares.

All shrub species were measured in a randomly chosen quadrant from the
center point and measured between the transect tapes spread in 4
cardinal directions. All shrubs rooted within 3 meters from the center
point were identified to species and the number per species, each
individual height, widths, and decadence were recorded. Plant canopy
cover was measured using the line intercept method. The same transect
tape was spread across the habitat in 4 cardinal directions from the
center and read 15 m each way from the center point. Each species
encountered was measured as a distance in which it intersected the
transect tape. Distances were then analyzed as a proportion to the
entire distance (15 m) of the tape.

***Burrow Configuration***

Burrow systems or clusters were measured in order to identify any
pattern in the number of burrow openings, the distance between systems,
or the geometric shape of burrow clusters. At each burrow system where
fine scale habitat was measured, distances between openings and between
burrow systems were also measured. Once the average center point between
burrow openings was identified, the distance to the nearest opening was
measured. The next nearest opening to that one is measured and so forth
until all openings have been measured. The 2 farthest burrows from each
other (usually the first and the last) were measured to give an estimate
of the size of the system. A geometric shape of burrow opening placement
was also drawn and recorded. The nearest burrow system from the initial
system was found by walking concentric, ever-widening circles on the
outskirts of the burrow until the closest burrow system was found. The
distance from the center point of the initial burrow system to the
center of the second burrow system was measured with a rangefinder. The
same measurements are then made on the second burrow system as on the
first, as well as the activity classification recorded.

**RESULTS.**

***Occurrence, Distribution, and Abundance***

Walk transects were conducted for pygmy rabbit presence November 2004 to
September 2005. All evidence of pygmy rabbit presence (burrows, pellets,
tracks, and visuals of rabbits) was recorded. Surveys were also
conducted in areas where pre-treatment surveys had been conducted by the
BLM and were resurveyed by the investigators. BLM surveys identified 118
active burrow systems and 85 inactive systems. In BYU studies, 14 active
burrow systems and all others in treatments were acknowledged as
inactive systems in the same areas. Statewide occurrence surveys were
also accomplished concomitantly with the funds secured by the
cooperator, the Utah Division of Wildlife Resources (UDWR).

Derivations of pygmy rabbit abundance estimates have been documented in
various ways throughout their range (Rachlow and Whitham 2004; Bartels
and Hays 2001; Smith 1978). However most of these estimates have
included indirect surveys using burrow evidence and likely overestimate
abundance since individual rabbits seasonally utilize more than one
burrow system (Rachlow and Whitham 2004; pers. obs.). Rachlow and
Whitham (2004) have developed an extrapolation method from their live
trapping data and line transect surveys of active burrows. These methods
allow for crude density estimate comparisons by using their estimate of
1.84 active burrows per rabbit (Table 1). The investigators here
recorded burrow density from walking 250 m line transects through
homogenous big sagebrush habitat and, using a GPS, recorded where all
active and inactive burrows were seen. Active burrow measurements were
recorded and then analyzed using the software Distance 5.0 Beta 3.
Burrow densities with this method were estimated at 1.46 burrows/ha
using Akiake's Criterion for a Half-normal key function with a hermite
polynomial adjustment for a detection function model (N = 212; CI =
1.24; 1.72; AICc = 1028.8). Using this value and Rachlow and Whitham's
(2004) extrapolation, the abundance values can be compared to values
found in Idaho (Table 1).

+---+--------------------------------+-------------+------------------+
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+---+--------------------------------+-------------+------------------+
|   | **Location**                   | **Burrow    | **Extrapolated** |
|   |                                | Density**   |                  |
|   |                                |             | **Mark/Recap.    |
|   |                                |             | Density**        |
+---+--------------------------------+-------------+------------------+
| 1 | Cedar Gulch, Leadore, Idaho    | 0.7         | 0.38 rabbits/ha  |
| \ |                                | burrows/ha  |                  |
| . |                                |             |                  |
+---+--------------------------------+-------------+------------------+
| 2 | Rocky Canyon, Leadore, Idaho   | 1.0         | 0.54 rabbits/ha  |
| \ |                                | burrows/ha  |                  |
| . |                                |             |                  |
+---+--------------------------------+-------------+------------------+
| 3 | Warm Springs, Leadore, Idaho   | 5.0         | 2.72 rabbits/ha  |
| \ |                                | burrows/ha  |                  |
| . |                                |             |                  |
+---+--------------------------------+-------------+------------------+
| 4 | Grass Valley, Utah             | 1.46        | 0.79 rabbits/ha  |
| \ |                                | b           |                  |
| . |                                | urrows/ha\* |                  |
+---+--------------------------------+-------------+------------------+
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| g |                                |             |                  |
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| . |                                |             |                  |
+---+--------------------------------+-------------+------------------+

**Habitat Use**

At burrow locations, habitat characteristics were similar to
characteristics found at random, unoccupied habitat with slight
variations (Table 2). Shrub height was higher at burrow locations and
individual shrub canopy area was significantly larger than shrubs in
random sites and unoccupied sites (Tables 2 and 3). Sagebrush spatial
pattern index measures the uniformity of plant spacing and any
measurement greater than 0.5 suggests a clumped pattern (Ludwig and
Reynolds 1988). At burrow systems and unoccupied random sites spatial
pattern was slightly below a clumped dispersion pattern (SPI = 0.47).
However, occupied habitat was a clumped pattern (SPI = 0.60). Average
shrub density also gives an indication of dispersion and spacing between
shrubs, however, burrow systems had the lowest value (2,630.71 cm²),
indicating the most clumped pattern and random sites as the most open
dispersion (4,168 cm²),

Species composition in all three categories is predominantly big
sagebrush (i.e. ARTR). Occupied pygmy rabbit habitat (home range
measurements) had notably more big sagebrush than did burrow locations
or unoccupied habitat (97%, 88%, and 83% respectively). Black sagebrush
(i.e. ARNO) was only found intermixed in areas where pygmy rabbits did
not occur. Big rabbitbrush (i.e. CHNA) is noted as a disturbance species
and was found more common at burrow sites and in unoccupied habitat.

+-----------+------------+-------+---------+--------+-------+--------+
| **Table   |            |       |         |        |       |        |
| 2.**      |            |       |         |        |       |        |
| De        |            |       |         |        |       |        |
| scriptive |            |       |         |        |       |        |
| s         |            |       |         |        |       |        |
| tatistics |            |       |         |        |       |        |
| for       |            |       |         |        |       |        |
| habitat   |            |       |         |        |       |        |
| mea       |            |       |         |        |       |        |
| surements |            |       |         |        |       |        |
| taken at  |            |       |         |        |       |        |
| burrow    |            |       |         |        |       |        |
| sires,    |            |       |         |        |       |        |
| habitat   |            |       |         |        |       |        |
| from      |            |       |         |        |       |        |
| transect  |            |       |         |        |       |        |
| data      |            |       |         |        |       |        |
| found     |            |       |         |        |       |        |
| within a  |            |       |         |        |       |        |
| pygmy     |            |       |         |        |       |        |
| rabbit's  |            |       |         |        |       |        |
| home      |            |       |         |        |       |        |
| range,    |            |       |         |        |       |        |
| and       |            |       |         |        |       |        |
| compared  |            |       |         |        |       |        |
| with data |            |       |         |        |       |        |
| found at  |            |       |         |        |       |        |
| random,   |            |       |         |        |       |        |
| u         |            |       |         |        |       |        |
| noccupied |            |       |         |        |       |        |
| habitat.  |            |       |         |        |       |        |
+-----------+------------+-------+---------+--------+-------+--------+
|           | **Shrub    | **    | **Shrub | *      | **    | *      |
|           | Com        | Shrub | Ave.    | *Shrub | Shrub | *Shrub |
|           | position** | Ave.  | Deca    | Ave.   | Sp    | Canopy |
|           |            | Hei   | dence** | Den    | atial | Area** |
|           |            | ght** |         | sity** | Pa    |        |
|           |            |       |         |        | ttern |        |
|           |            |       |         |        | In    |        |
|           |            |       |         |        | dex** |        |
+-----------+------------+-------+---------+--------+-------+--------+
| **Burrow  | ARTR       | 69.75 | 55.74%  | 2      | 0.474 | 10     |
| Lo        |            | cm    |         | 630.71 |       | 711.88 |
| cations** | N = 205    |       | N = 288 | cm²    | N =   | cm²    |
|           | (88%)      | N =   |         |        | 24    |        |
| **(3 m    |            | 288   |         | N = 24 |       | N =    |
| radius)** | CHNA       |       |         |        |       | 144    |
|           |            |       |         |        |       |        |
|           | N = 28     |       |         |        |       |        |
|           | (12%)      |       |         |        |       |        |
|           |            |       |         |        |       |        |
|           | No other   |       |         |        |       |        |
|           | shrubs     |       |         |        |       |        |
+-----------+------------+-------+---------+--------+-------+--------+
| **I       | ARTR       | 45.68 | 50.94 % | 3      | 0.601 | 14     |
| dentified |            | cm    |         | 385.26 |       | 542.17 |
| Pygmy     | N = 967    |       | N =     | cm²    | N =   | cm²    |
| Habitat/  | (97%)      | N =   | 1000    |        | 500   |        |
| Home      |            | 1000  |         | N =    |       | N =    |
| Range**   | CHNA       |       |         | 500    |       | 1000   |
|           |            |       |         |        |       |        |
| **        | N = 27     |       |         |        |       |        |
| (transect | (3%)       |       |         |        |       |        |
| data)**   |            |       |         |        |       |        |
|           | No other   |       |         |        |       |        |
|           | shrubs     |       |         |        |       |        |
+-----------+------------+-------+---------+--------+-------+--------+
| **Random  | ARTR       | 44.61 | 47.33 % | 4      | 0.471 | 3      |
| Sites**   |            | cm    |         | 168.82 |       | 314.01 |
|           | N = 99     |       | N = 152 | cm²    | N =   | cm²    |
| **(unoc   | (83%)      | N =   |         |        | 11    |        |
| cupied)** |            | 152   |         | N = 11 |       | N = 76 |
|           | CHNA       |       |         |        |       |        |
|           |            |       |         |        |       |        |
|           | N = 1 (1%) |       |         |        |       |        |
|           |            |       |         |        |       |        |
|           | CHVI       |       |         |        |       |        |
|           |            |       |         |        |       |        |
|           | N = 4 (3%) |       |         |        |       |        |
|           |            |       |         |        |       |        |
|           | ARNO       |       |         |        |       |        |
|           |            |       |         |        |       |        |
|           | N = 15     |       |         |        |       |        |
|           | (13%)      |       |         |        |       |        |
+-----------+------------+-------+---------+--------+-------+--------+

A subsample was derived from shrub variables measured and reported in
Table 2. These subsamples were then used to compare shrub
characteristics in occupied pygmy rabbit home range, at burrow
locations, and in unoccupied habitat. Burrow sites were significantly
different than occupied and unoccupied habitat in all three parameters
identified.

+-----------------+----------------+----------------+-----------------+
| Table 3.        |                |                |                 |
| Paired-t test   |                |                |                 |
| results for 3   |                |                |                 |
| distinctive     |                |                |                 |
| parameters      |                |                |                 |
| found in pygmy  |                |                |                 |
| rabbit habitat  |                |                |                 |
| compared with   |                |                |                 |
| random,         |                |                |                 |
| unoccupied      |                |                |                 |
| habitat         |                |                |                 |
+-----------------+----------------+----------------+-----------------+
| N = 146         | Burrow to Home | Burrow to      | Unoccupied to   |
|                 | Range Habitat  | Unoccupied     | Home Range      |
|                 | Comparison     | Habitat        | Habitats        |
|                 |                | Comparison     | Comparison      |
+-----------------+----------------+----------------+-----------------+
| **Percent Shrub | T = 2.98       | T = -2.78      | T = -0.04       |
| Decadence**     |                |                |                 |
|                 | **P = 0.003**  | **P = 0.006**  | P = 0.970       |
|                 |                |                |                 |
|                 | CI = 3.88;     | CI = -20.00;   | CI = -7.93;     |
|                 | 19.18          | -3.36          | 7.63            |
+-----------------+----------------+----------------+-----------------+
| **Shrub         | T = -6.54      | T = -7.04      | T = 0.12        |
| Height**        |                |                |                 |
|                 | **P = 0.000**  | **P = 0.000**  | P = 0.902       |
|                 |                |                |                 |
|                 | CI = -34.67;   | CI = -34.62;   | CI = -6.31;     |
|                 | -18.56         | -19.45         | 7.14            |
+-----------------+----------------+----------------+-----------------+
| **Shrub Canopy  | T = -2.33      | T = -5.14      | T = -7.76       |
| Cover Area**    |                |                |                 |
|                 | **P = 0.021**  | **P = 0.000**  | **P = 0.000**   |
|                 |                |                |                 |
|                 | CI = -9064;    | CI = -9993;    | CI = -15214;    |
|                 | -752           | -4441          | -9036           |
+-----------------+----------------+----------------+-----------------+

Species composition was further investigated using quarter-meter
understory plots at burrow locations compared with unoccupied, random
habitat (Table 4). Burrow locations had consistently more big sagebrush
than random locations, and had little understory of forbs and grasses
(less than 13% total understory). Unoccupied, random habitat was
partially dominated by big sagebrush but had more forbs and grasses than
the other sites.

+----------------+---------+----------+----------+---------+---------+
| **Table 4.     |         |          |          |         |         |
| Spring-summer  |         |          |          |         |         |
| plant species  |         |          |          |         |         |
| composition at |         |          |          |         |         |
| burrow sites   |         |          |          |         |         |
| and            |         |          |          |         |         |
| unoccupied,    |         |          |          |         |         |
| random sites   |         |          |          |         |         |
| in understory  |         |          |          |         |         |
| ¼ m² plots are |         |          |          |         |         |
| compared here. |         |          |          |         |         |
| Shrub species  |         |          |          |         |         |
| are separated  |         |          |          |         |         |
| for dominant   |         |          |          |         |         |
| species        |         |          |          |         |         |
| comparisons    |         |          |          |         |         |
| and grasses    |         |          |          |         |         |
| and forbs are  |         |          |          |         |         |
| clumped        |         |          |          |         |         |
| because of     |         |          |          |         |         |
| variation      |         |          |          |         |         |
| between        |         |          |          |         |         |
| treatment      |         |          |          |         |         |
| sites and      |         |          |          |         |         |
| active burrow  |         |          |          |         |         |
| sites.         |         |          |          |         |         |
| Residual       |         |          |          |         |         |
| proportions of |         |          |          |         |         |
| materials were |         |          |          |         |         |
| moss/lichen or |         |          |          |         |         |
| abiotic        |         |          |          |         |         |
| factors,       |         |          |          |         |         |
| including bare |         |          |          |         |         |
| ground,        |         |          |          |         |         |
| litter, and    |         |          |          |         |         |
| rock.**        |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| **DIRECTION**  | **BIG   | **BIG    | **LITTLE | **BLACK | **FORBS |
|                | SAGE    | RABBI    | RABBI    | SAGE    | AND     |
|                | BRUSH** | TBRUSH** | TBRUSH** | BRUSH** | GR      |
|                |         |          |          |         | ASSES** |
+----------------+---------+----------+----------+---------+---------+
| N = 24         | **4     | 5.17%    | 0.00%    | 0.00%   | 7.76%   |
|                | 6.99%** |          |          |         |         |
| Burrow center  |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 24         | **3     | 3.24%    | 0.00%    | 0.00%   | 9.47%   |
|                | 9.38%** |          |          |         |         |
| North of       |         |          |          |         |         |
| Burrow         |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 24         | **3     | 0.60%    | 0.00%    | 0.00%   | 6.13%   |
|                | 3.19%** |          |          |         |         |
| East of Burrow |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 24         | **3     | 4.02%    | 0.00%    | 0.00%   | 10.56%  |
|                | 9.90%** |          |          |         |         |
| South of       |         |          |          |         |         |
| Burrow         |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 24         | **3     | 3.23%    | 0.00%    | 0.00%   | 12.80%  |
|                | 5.20%** |          |          |         |         |
| West of Burrow |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 11         | **2     | 0.00%    | 0.00%    | 7.43%   | 17.10%  |
|                | 8.35%** |          |          |         |         |
| Random center  |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 11         | **2     | 0.00%    | 0.63%    | 0.00%   | **2     |
|                | 4.39%** |          |          |         | 3.44%** |
| North of       |         |          |          |         |         |
| Random Center  |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 11         | 31.00%  | 0.00%    | 0.90%    | 0.45%   | **6     |
|                |         |          |          |         | 7.31%** |
| East of Random |         |          |          |         |         |
| Center         |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 11         | 11.85%  | 0.00%    | 0.44%    | 0.00%   | **2     |
|                |         |          |          |         | 0.20%** |
| South of       |         |          |          |         |         |
| Random Center  |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+
| N = 11         | 18.80%  | 0.00%    | 0.00%    | 0.00%   | **2     |
|                |         |          |          |         | 2.56%** |
| West of Random |         |          |          |         |         |
| Center         |         |          |          |         |         |
+----------------+---------+----------+----------+---------+---------+

The abundance of shrub species at burrow sites was investigated using an
area count method and then compared to similar data in unoccupied,
random locations (Table 5). Over 95% of plants observed in the randomly
chosen quarter of a burrow site (area = 7.07 m²; r = 3 m) were big
sagebrush plants while only 57.86% of plants were big sagebrush in
random, unoccupied sites. More shrub species were found in unoccupied,
random locations; however these species are virtually unpalatable to
pygmy rabbits (Table 5). The most abundant shrub per m² was big
sagebrush for burrow sites (2.97/ m²) and random locations (0.88/ m²).
Black sagebrush was also abundant in random sites (0.52/ m²) but only at
limited sites measured. Burrow sites had collectively more shrubs
present than did unoccupied, random sites (0.78/m² and 0.38/m²
respectively).

+------------+------------+---------------+------------+--------------+
| **Table 5. |            |               |            |              |
| All shrub  |            |               |            |              |
| density    |            |               |            |              |
| was        |            |               |            |              |
| measured   |            |               |            |              |
| in a 3 m   |            |               |            |              |
| quarter    |            |               |            |              |
| radius     |            |               |            |              |
| (7.07 m²)  |            |               |            |              |
| in a       |            |               |            |              |
| random     |            |               |            |              |
| direction  |            |               |            |              |
| from a     |            |               |            |              |
| burrow     |            |               |            |              |
| site.      |            |               |            |              |
| These      |            |               |            |              |
| me         |            |               |            |              |
| asurements |            |               |            |              |
| were then  |            |               |            |              |
| compared   |            |               |            |              |
| to random  |            |               |            |              |
| sites in   |            |               |            |              |
| unoccupied |            |               |            |              |
| habitat.** |            |               |            |              |
+------------+------------+---------------+------------+--------------+
| **SHRUB    | **Burrow   | **Proportion  | **Random   | **Proportion |
| SPECIES**  | Species    | of Total      | Species    | of Total     |
|            | Count      | Burrow Shrub  | Count      | Random       |
|            | (pl        | Species**     | (pl        | Species**    |
|            | ants/m²)** |               | ants/m²)** |              |
+------------+------------+---------------+------------+--------------+
| Big        | N = 504    | 95.45%        | N = 81     | 57.86%       |
| Sagebrush  |            |               |            |              |
|            | Ave =      |               | Ave =      |              |
|            | 2.97/m²    |               | 0.88/m²    |              |
+------------+------------+---------------+------------+--------------+
| Big        | N = 24     | 4.55%         | N = 1      | 0.71%        |
| R          |            |               |            |              |
| abbitbrush | Ave =      |               | Ave =      |              |
|            | 0.14/m²    |               | 0.01/m²    |              |
+------------+------------+---------------+------------+--------------+
| Little     | N = 0      | 0.00%         | N = 10     | 7.14%        |
| R          |            |               |            |              |
| abbitbrush | Ave =      |               | Ave =      |              |
|            | 0.00/m²    |               | 0.11/m²    |              |
+------------+------------+---------------+------------+--------------+
| Black      | N = 0      | 0.00%         | N = 48     | 34.29%       |
| Sagebrush  |            |               |            |              |
|            | Ave =      |               | Ave =      |              |
|            | 0.00/m²    |               | 0.52/m²    |              |
+------------+------------+---------------+------------+--------------+
| **Total**  | **N =      |               | **N =      |              |
|            | 528**      |               | 140**      |              |
| **Shrubs** |            |               |            |              |
|            | **Ave =    |               | **Ave =    |              |
|            | 0.78/m²**  |               | 0.38/m²**  |              |
+------------+------------+---------------+------------+--------------+

Horizontal obscurity was also measured at burrow locations and compared
to random, unoccupied habitat (Table 6). Burrow locations consistently
had a higher proportion of obscured squares on the cover board than did
random, unoccupied locations at all distances (paired t-test; T = 10.84;
p \< 0.001 N = 12; CI = 25.57%; 38.60%). Obscurity differed in cover
percent at different distances as well. In random sites, distances 2.5 m
away from the center location had lower obscurity values than distances
10 m away (paired t-test; T = 5.50; p \< 0.001; N = 52; CI = 14.28%;
30.72%). Values at burrow sites 10 m away from the center average
greater than 90% and are significantly different at the 2.5 m and 10 m
distances (paired t-test; T = 5.20; p = 0.000; N = 95; CI = 11.30%;
25.27%). In burrow locations, obscurity estimates at 2.5 m from the
center of the burrow entries are even larger than values found at 10 m
on random sites (2 sample t; T = 2.20; p = 0.028; CI = 1.4%; 24.10%).

  ------------------ ------------------------- --------------------------
  **Table 6. Average                           
  percent horizontal                           
  obscurity from                               
  selected distances                           
  from burrow sites                            
  and compared to                              
  random sites in                              
  unoccupied                                   
  habitat.**                                   

  **Direction and    **Percent Obscurity at    **Percent Obscurity at
  Distance**         Burrow Sites (N = 24)**   Random Sites (N = 13)**

  **North @ 2.5      66.00%                    29.06%
  Meters**                                     

  **North @ 5        77.00%                    44.02%
  Meters**                                     

  **North @ 10       91.00%                    53.21%
  Meters**                                     

  **East @ 2.5       75.00%                    41.45%
  Meters**                                     

  **East @ 5         84.00%                    59.62%
  Meters**                                     

  **East @ 10        86.00%                    67.74%
  Meters**                                     

  **South @ 2.5      76.00%                    26.07%
  Meters**                                     

  **South @ 5        87.00%                    43.80%
  Meters**                                     

  **South @ 10       94.00%                    54.06%
  Meters**                                     

  **West @ 2.5       71.00%                    50.85%
  Meters**                                     

  **West @ 5         84.00%                    65.17%
  Meters**                                     

  **West @ 10        91.00%                    62.39%
  Meters**                                     

  **t-test:**        **T = 10.84; P = 0.000**  
  ------------------ ------------------------- --------------------------

Macrohabitat was measured quantitatively by measuring the distances of
specific parameters from the center point of the burrow and then
compared to random, unoccupied habitat measurements. Sample sizes were
too small to analyze any important data; however averages are reported
(Table 7).

  -------------------------- ---------------------- ----------------------
  **Table 7. Average                                
  distances from 8                                  
  macrohabitat parameters                           
  are shown here. Nearest                           
  known parameter was                               
  measured.**                                       

  **Macrohabitat Parameter** **Burrow Site          **Random, Unoccupied
                             Habitat**              Habitat**

  **Distance from            **48.5 m (N = 24)**    **25.3 m (N = 11)**
  Human-caused edge**                               

  **Distance from Natural    **413.8 m (N = 23)**   **405.8 m (N = 10)**
  edge**                                            

  **Distance from Human      **102.5 m (N = 24)**   **52.0 m (N = 11)**
  Structure**                                       

  **Distance from ORV        **93.3 m (N = 23)**    **32.5 m (N = 11)**
  trails**                                          

  **Distance from big        **0.51 m (N = 23)**    **0.53 m (N = 7)**
  sagebrush plant**                                 

  **Distance from big        **119.1 m (N = 22)**   **79.4 m (N = 9)**
  rabbitbrush plant**                               

  **Distance from ungulate   **12.9 m (N = 15)**    **13.8 m (N = 2)**
  sign**                                            

  **Distance from predator   **13.8 m (N = 15)**    **65.5 m (N = 2)**
  sign**                                            

  **Distance from nearest    **302.3 m (N = 24)**   **245.7 m (N = 11)**
  raptor perch**                                    
  -------------------------- ---------------------- ----------------------

**Burrow System Configuration and Activity Levels**

Burrow system configuration (i.e. geometric shape), activity level
classification (Rachlow and Whitham 2004), number of entries, and the
distance between burrow openings and between systems were measured.
Burrow systems were recorded and given an activity classification and
the number of openings recorded as well (Table 8). The number of burrow
openings averaged 1.98 per system (N =250) with 7 as the maximum
openings in line transect surveys. The proportion of active burrows
(category 1) was almost as much as all other classifications combined
(47.44% of burrow systems were category 1 and 52.56% total burrow
systems were in categories 2-4).

  ------------------------- --------------------- -----------------------
  Table 8. Number of                              
  burrows observed and the                        
  total per activity                              
  classification.                                 

  Burrow Classification     Total Burrow Systems  Proportion of Total
                            Encountered           Burrow Systems
                                                  Encountered

  Cat. 1 = Active burrow    N = 102               47.44%
  openings                                        

  Cat. 2 = Recently active  N = 49                22.79%
  burrow openings                                 

  Cat. 3 = Old burrow       N = 23                10.70%
  openings                                        

  Cat. 4 = Very old burrow  N = 41                19.07%
  openings                                        

  **TOTAL:**                **N = 215**           
  ------------------------- --------------------- -----------------------

The number of burrow openings was recorded on each burrow system
included in habitat analyses (Table 9). The most abundant type were
single opening burrows and 49.2% were found with only one entry (N = 32)
while multiple entry burrows were only slightly more common (50.8%; N =
33). Single opening burrow systems were the most common nearest neighbor
of the random burrow being measured (N = 33). On the nearest neighbor
measurements, 75.76% (N = 25 of 33) of burrows had a single opening
burrow adjacent to it. Of these nearest burrows, single entry burrows
were 60.6% more common adjacent to a multiple entry burrow system (N =
20 out of 33) while a multiple entry, adjacent burrow was not as common
next to a multiple entry burrow (24.2% or N = 8 out of 33). Using a
Chi-square maximum likelihood test, a nearest neighbor burrow was 99.7%
more likely to be a single entry burrow next to a multiple opening
burrow than a multiple entry burrow system (p = 1.00; X² = 0.997; N =
65).

Distance to the nearest neighbor burrow system also appeared to be
correlated with whether the burrow system was a single opening or
multiple opening burrow system (Pearson = 0.414; p = 0.018; N = 65).
Burrow systems with multiple entries averaged 114.0 m away from the next
nearest burrow system where there were multiple entries while nearest
systems with multiple entries to single entry burrows averaged 52.2 m
away. Single entry burrow systems averaged 12.8 m away from the nearest
systems with one entrance.

  ----------------- ------------- ---------------- ------------------ ------------
  **Table 9. The                                                      
  number of burrow                                                    
  openings or                                                         
  entries per                                                         
  burrow system                                                       
  encountered as                                                      
  well as the                                                         
  geometric shape                                                     
  of the burrow                                                       
  systems are                                                         
  reported here.**                                                    

  **No. Openings/   **Total       **Proportion**   **Burrow System    **Number**
  Entries**         Observed**                     Shape**            

  1 Entry           32            49.2%            One opening        9

  2 Entries         7             10.6%            Triangle Shaped    9

  3 Entries         8             12.3%            "Y" Shaped         1

  4 Entries         9             13.8%            Oval Shaped        7

  5 Entries         6             9.2%             Boot Shaped        2

  6 Entries         3             4.5%             "T" Shaped         1

  No habitat                                       Diamond Shaped     1
  completed on 7                                                      
  entries to date                                                     

  Total Multiple    33            50.8%            Box/Square Shaped  1
  Entries                                                             

  **Total:**        **65**                         **8 General        **31**
                                                   Shapes**           
  ----------------- ------------- ---------------- ------------------ ------------

Within a burrow system the distances between openings were measured.
Burrows with multiple entries had nearest to next nearest entrances
measured until all burrows were measured. Burrow openings became
increasingly farther apart as the number of burrows increased (Table
10). Though sample size is relatively small (Table 10), the variation in
distances between the first and second entries to further out openings
(i.e. third to fourth, fourth to fifth and fifth to sixth openings) is
significantly different, with first and second openings closer than the
progressive openings (t-test: T = -3.92; p = 0.001; CI = -151.5; -47.3;
N = 28).

Direction of the next nearest burrow system was also recorded. The most
common direction for a nearest burrow system from the randomly chosen
burrow system was southwest (N = 7 out of 23 or 30.43%) and no burrows
were found in a northwest direction (N = 0 out of 23). Additional
information needs to be collected on this, as the sample size is too
small to investigate these data further.

+------------------------------------+-----------+--------------------+
| Table 10. Average distances in     |           |                    |
| burrow configurations both between |           |                    |
| openings per cluster (i.e. burrow  |           |                    |
| system) and next closest cluster   |           |                    |
| are reported.                      |           |                    |
+------------------------------------+-----------+--------------------+
|                                    | Average   | Sample Size        |
|                                    | Distance  |                    |
+------------------------------------+-----------+--------------------+
| Average distance from center of    | 66.20 cm  | N = 35             |
| the burrow system to the first     |           |                    |
| opening                            |           |                    |
+------------------------------------+-----------+--------------------+
| Average distance from the first    | 100.53 cm | N = 34             |
| opening to the second opening      |           |                    |
+------------------------------------+-----------+--------------------+
| Average distance from the second   | 160.69 cm | N = 26             |
| opening to the third opening       |           |                    |
+------------------------------------+-----------+--------------------+
| Average distance from the third    | 174.83 cm | N = 18             |
| opening to the fourth opening      |           |                    |
+------------------------------------+-----------+--------------------+
| Average distance from the fourth   | 185.11 cm | N = 9              |
| opening to the fifth opening       |           |                    |
+------------------------------------+-----------+--------------------+
| Average distance from the fifth    | 216.00 cm | N = 3              |
| opening to the sixth opening       |           |                    |
+------------------------------------+-----------+--------------------+
| Average distance between the       | 193.86 cm | N = 90             |
| nearest and farthest openings      |           |                    |
+------------------------------------+-----------+--------------------+
| Average distance from one burrow   | 58.84 m   | N = 32             |
| system to the next nearest burrow  |           |                    |
| system                             |           |                    |
+------------------------------------+-----------+--------------------+
| Major direction of nearest burrow  | Southwest | N = 7 southwest    |
| system (S, SE, SW, N, NE, NW, E,   |           |                    |
| or W)                              |           | N = 23 total       |
|                                    |           | directions         |
|                                    |           | recorded           |
+------------------------------------+-----------+--------------------+

**Camera Data**

Aside from identifying species utilizing pygmy rabbit burrows, remote
cameras were useful in recording times of use. Pygmy rabbits caught on
camera were also recorded with a time and date log. Pygmy rabbits were
more often active during crepuscular times (Table 11) and were seen
71.76% more frequently at these times. Using a binomial probability
distribution depicting crepuscular activity, pygmy rabbits were 51.70%
more likely to be found active at crepuscular hours than at night or day
(z = 0.517, N = 665). Time and temperature likely play a factor in
activity patterns, however summer sample size was too small to see if
there was seasonality to the activity times.

  ------------------ -------------------------- --------------------------
  Table 11. Pygmy                               
  rabbit activity at                            
  burrows was                                   
  observed using                                
  Trailmaster 1500                              
  digital cameras                               
  and the time of                               
  capture recorded.                             
  Crepuscular was                               
  defined as two                                
  hours before or                               
  after daylight.                               

                     **Count Number**           **Proportion**

  **Night Activity** 42                         16.03%

  **Crepuscular      188                        71.76%
  Activity**                                    

  **Day Activity**   32                         12.21%

  ***TOTAL:***       **262**                    
  ------------------ -------------------------- --------------------------

**CONCLUSIONS.**

**Occurrence and Distribution**

Fewer active burrows remained on re-walked treatment sites. However,
some GPS locations could have been incorrect because some were in the
middle of treatment areas where all sagebrush had been removed, the soil
disturbed, and no burrows could be found. The numbers of active burrow
systems were much smaller in areas where investigators re-surveyed
former BLM surveys prior to sagebrush treatments. This is likely because
some burrows were missed in BLM surveys and active colonies are still
present. Many burrows labeled active in BLM surveys are now inactive,
however.

**Abundance**

Our density estimation value for Grass Valley is intermediate in
comparison to recent (2002-2003) data in Idaho. However, these data may
be considered a low density population because it only documents areas
where pygmy rabbits were active during this study and not areas where
rabbits were formerly found. This estimate is subsequently of patchy
areas at a small scale and loss of metapopulations and connectivity is
not attributed in this estimate.

The comparable Idaho densities were also considered by Rachlow and
Whitham (2004) as low at all of their study areas yet represented some
of the most robust pygmy rabbit populations in Idaho. By reference,
these abundance estimates also likely represent the largest in the
entire range as Idaho is thought to have the largest distribution,
highest densities and best habitat. Caution should also be used in using
the density estimations, as not all areas may have 1.84 burrow systems
per rabbit. Months where no young are present an individual rabbit can
likely use 3-10 different burrow systems per season (Rachlow and Whitham
2004). Camera data have elucidated such likely behaviors in our study,
however individual identification tags on rabbits are needed to validate
camera data as only one rabbit had identification on it this year.

**Habitat Use**

Burrow sites were significantly different than occupied and unoccupied
habitat in all three parameters identified. This suggests a site
selection process for burrow placement by pygmy rabbits, though
surrounding habitat is also utilized for foraging and cover (i.e. home
range habitat). Within the three parameters, the only significant
difference between occupied and unoccupied habitat was shrub canopy
cover size.

Shrub habitat characteristics at burrow sites compared with occupied and
unoccupied pygmy rabbit habitat support a selection pattern of pygmy
rabbits for areas where shrubs are higher and have a larger canopy than
surrounding habitat. This could be a function of older shrubs, but is
more likely a function of cover from predators, as more big rabbitbrush
(only useful for cover) was encountered at burrow sites than in the
other two habitats. However, shrubs at burrows were significantly more
decadent than those at the other habitats and are likely older as well
as taller. In the future, sagebrush should be aged by counting growth
rings to answer this question.

Grass Valley is unique to other pygmy rabbit habitats the investigators
have observed in that pygmy rabbits heavily utilize former Utah prairie
dog (*Cynomys parvidens*) burrows when they occur in sagebrush-dominated
habitat. This behavior likely skewed nearest neighbor measurements of
shrubs and thus is why parameters such as shrub overstory (i.e. shrub
canopy cover) seem on average higher estimates at burrow sites than in
surrounding home range habitat. However, consistent with other pygmy
rabbit habitat studies, shrubs are significantly taller at burrow sites
than in the other habitat categories and cover is likely more important
in foraging areas (i.e. home range habitat category) than at the burrow
where escape into the burrow is available.

Shrub species at burrow locations, occupied home range habitat, and
unoccupied habitat were all predominantly big sagebrush (greater than
83% shrub composition). Little rabbitbrush was observed as1% of the
shrubs in unoccupied habitat. No little rabbitbrush or black sagebrush
was recorded in pygmy rabbit habitat. Big rabbitbrush was the next most
common shrub and was more abundant at burrow locations than the other
habitat types. A larger proportion of big rabbitbrush at burrow sites
(12%) can likely by accounted for by (1) soft soils that would be
present since big rabbitbrush is an indicator of soil disturbance and
(2) big rabbitbrush may not be a palatable species to pygmy rabbits but
is an excellent cover species with a wide overstory canopy. Big
rabbitbrush also folds over when it becomes older making ideal above
ground tunnels that rabbits may use temporarily and therefore may
occasionally be selected for by pygmy rabbits (pers. obs.).

Almost all shrubs encountered in pygmy rabbit home range habitat were
big sagebrush. Big sagebrush is most important in these foraging
grounds, since pygmy rabbits rely on sagebrush as their primary food
source. It should also be noted that though there is little diversity of
other shrubs in all 3 categories, the other 2 species identified were
more undesirable, disturbance species and that big sagebrush was the
species most conducive to active cover, foraging, and a positive,
dominant ecotype species for most wildlife. Shrub density data support
this and show big sagebrush as the most common shrub species 95.45% of
the time and big rabbitbrush occurring only 4.55% of the time.

While big sagebrush dominated all burrow sites, there was a lack of
forbs and grasses in understory data. Forbs and grasses were more common
in random locations and collectively dominated the ratio of big
sagebrush on average. While some of these forbs are exotic and/or are
unpalatable, the presence of forbs and grasses in pygmy rabbit diet in
the summer is critical. The disparity of forbs and grasses in pygmy
rabbit burrow habitat is likely a negative factor and could explain why
individual rabbits appear to have such large home ranges compared to
former studies (Smith and Flinders 1980b).

Shrub cover was also directly measured with the horizontal obscurity
board. Obscurity was significantly denser at burrow locations than at
random, unoccupied habitat. Pygmy rabbits likely select habitat with the
most cover and rely on this as a major function of predator avoidance.
As expected, in both burrow and random locations horizontal cover is
heavier farther away from the center point (i.e. 10 m versus 2.5 m).
However, cover at burrow systems is so thick that estimates close to the
burrow (2.5 m) are comparable to estimates at the densest points (10 m)
at the random sites.

**Burrow Configuration**

Active burrows were much more common than other activity classifications
and support the assertion that pygmy rabbits maintain more than one
burrow system. However, inactive burrows likely play a crucial role in
escape cover, as seen by video from remote cameras. Cameras have been
placed on burrows classified as old or very old and pygmy rabbit use has
been recorded.

Single entry burrow systems were more common than expected, particularly
since they are so much harder to detect than multiple entry burrows.
Former surveys took single entry burrows into little consideration
(Greenwood, pers. comm.) because they were thought to not be important
to pygmy rabbit habitat needs. However, single burrows maybe a function
of a larger distance needed for foraging and habitat data collected here
elude to this. Anecdotal evidence supports that rabbits, particularly
juveniles, will flee observers to a nearest burrow (which is usually
only one opening). Often these burrows are shallow and less than half a
meter in depth and could likely be used exclusively for escape cover.
Distance between a burrow system and its nearest neighbor also supports
the use of single entry burrows as escape cover. The fewer openings the
burrow system had, the closer the system was to its next nearest burrow.

Multiple burrow systems were more often in a triangular or oval shape.
The distance between openings also increased with the increase in number
of openings. Both the system shape and the distance between openings may
be a function of the burrows being former Utah prairie dog burrows.
Pygmy rabbit burrow systems outside of Grass Valley would have to be
looked at to draw any conclusions about burrow shape and size selection.

**Camera Data**

Pygmy rabbit activity times were examined using remote cameras. Pygmy
rabbits were primarily crepuscular, but appeared to be active at other
times as well. Seasonality and/or temperature likely play a strong role
in activity times, however our sample size was too small to break the
data into seasons or climatic changes.

**DISCUSSION.**

This study was established to be a multi-year project and conclusions
drawn from the results should take this into consideration. Data
reported here are inconclusive until more research can be added to this
study. Occurrences of pygmy rabbits throughout the Valley were
comprehensively studied yet some colonies may have been missed. Research
into where rabbits are, their abundances, movement behavior, and habitat
use ideally needs to be studied further.

The abundance of pygmy rabbits in Grass Valley, Utah were found to be
midrange when compared to values estimated in Idaho. In the habitat most
similar to Grass Valley (i.e. Rocky Gulch), estimated density was 0.54
rabbits/ha and is comparable to our extrapolated value of 0.79
rabbits/ha. These values likely represent a lower abundance estimate
than historical values, though both areas probably represent the highest
abundances in their respective state. This is based on the observation
by managers and researchers that these two areas have the most rabbits
in each of their states (Rachlow and Whitham 2004).

Pygmy rabbits appear to utilize habitat based on predator avoidance and
browse forage needs. This makes big sagebrush puts in a critical role in
pygmy rabbit habitat use (Green and Flinders 1980b). Rabbits rely on
this shrub for cover and food and at least three-quarters of all shrubs
found in pygmy rabbit selected habitat was big sagebrush. Other species
also utilize sagebrush as a forage and cover species. Among these are
several species that are considered sagebrush obligate species (i.e.
besides the pygmy rabbit, the sage thrasher, sage sparrow, greater
sage-grouse, Brewer's sparrow, and mule deer are also considered
obligate - - McEwan et al. 1987; Braun et al. 1976). All but the sage
sparrow were encountered in Grass Valley and were found in large patches
of sagebrush also occupied by pygmy rabbits.

Burrows that were formerly prairie dog mounds were more open in
overstory cover. However, horizontal cover was consistently denser at
all burrows systems. This implies the importance of wide strips in
sagebrush removal projects so that cover is still available from
terrestrial predators. Burrow locations also had significantly taller
shrubs and suggests the need to leave patches of taller brush standing
for habitat expansion and not just areas where burrow openings occur.

Forb and grass species richness at burrow sites was significantly lower
than at random sites. Grasses in particular are important summer diet
materials for pygmy rabbits. Forbs and grasses important to get back
into pygmy rabbit home range, but caution should be used in sagebrush
removal. Treatment projects would likely be beneficial if sagebrush
stands were left in wide, connected corridors for rabbits to utilize
sagebrush as cover for movement and browse forage. Connectivity appears
to play an important role in whether pygmy rabbit will still occupy
sagebrush treatment mosaics. Active burrows encountered on re-walked
surveys of BLM treatment surveys were only found in sagebrush treatment
mosaics that were connected to other stands of sagebrush or swaths of
removal were much smaller and distances between one treatment island to
the next were minimal. Smaller, patchy removal of sagebrush was likely
the natural fire regime historically anyway. Big sagebrush is naturally
fire-limiting and can retard swift, large blazes more efficiently than
can grass-dominated ecotypes (Miller and Rose 1999; Winward 1991;
Winward 1984; Lommasson 1948).

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