BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Brachylagus idahoensis | Pygmy Rabbit 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Age at sexual maturity - Pygmy rabbits are capable of breeding when they
are about 1 year old [8,20].

Breeding season - The breeding season of pygmy rabbits is very short.
In Idaho it lasts from March through May; in Utah, from February through
March [22].

Gestation period and litter size - The gestation period of pygmy rabbits
is unknown.  It is between 27 and 30 days in various species of
cottontails (Sylvilagus spp.).  An average of six young are born per
litter and a maximum of three litters are produced per year [8].  In
Idaho the third litter is generally produced in June [20].  It is
unlikely that litters are produced in the fall [8].

Growth rate of juveniles - The growth rates of juveniles are dependent
on the date of birth.  Young from early litters grow larger due to a
longer developmental period prior to their first winter [8].

Mortality - The mortality of adults is highest in late winter and early
spring.  Green and Flinders [8] reported a maximum estimated annual
adult mortality of 88 percent in Idaho.  Juvenile mortality was highest
from birth to 5 weeks of age [8].

Pygmy rabbits may be active at any time of day; however, they are
generally most active at dusk and dawn.  They usually rest near or
inside their burrows during midday [8].


PREFERRED HABITAT : 
Pygmy rabbits are generally limited to areas on deep soils with tall,
dense sagebrush which they use for cover and food [4,8].  Individual
sagebrush plants in areas inhabited by pygmy rabbits are often 6 feet
(1.8 m) or more in height [4].  Extensive, well-used runways interlace
the sage thickets and provide travel and escape routes [8].  Dense
stands of big sagebrush along streams, roads, and fencerows provide
dispersal corridors for pygmy rabbits [17].

Burrows - The pygmy rabbit is the only native leporid that digs burrows.
Juveniles use burrows more than other age groups.  Early reproductive
activities of adults may be concentrated at burrows [8].  When pygmy
rabbits can utilize sagebrush cover, burrow use is decreased.  Pygmy
rabbits use burrows more in the winter for thermal cover than at other
times of the year [20].

Burrows are usually located on slopes at the base of sagebrush plants,
and face north to east.  Tunnels widen below the surface, forming
chambers, and extend to a maximum depth of about 3.3 feet (1 m).
Burrows typically have 4 or 5 entrances but may have as few as 2 or as
many as 10 [8].  In Oregon, pygmy rabbits inhabited areas where soils
were significantly deeper and looser than soils at adjacent sites.  Site
selection was probably related to ease of excavation of burrows [17].
In areas where soil is shallow pygmy rabbits live in holes among
volcanic rocks, in stone walls, around abandoned buildings, and in
burrows made by badgers (Taxidea taxus) and marmots (Marmota
flaviventris) [2,8].

Some researchers have found that pygmy rabbits never venture further
than 60 feet (21.3 m) from their burrows [2].  However, Bradfield [2]
observed pygmy rabbits range up to 328 feet (100 m) from their burrows.

Winter - Some areas inhabited by pygmy rabbits are covered with several
feet of snow for up to 2 or more months during the winter.  During
periods when the snow has covered most of the sagebrush, pygmy rabbits
tunnel beneath the snow to find food.  Snow tunnels are approximately
the same height and width as underground burrows.  They are quite
extensive and extend from one sagebrush to another [2,8].  Aboveground
movement during the winter months is restricted to these tunnel systems
[2].


COVER REQUIREMENTS : 
Pygmy rabbits are restricted to areas with heavy shrub cover [4,8].
Pygmy rabbits are seldom found in areas of sparse vegetative cover and
seem to be reluctant to cross open space [2].  In southeastern Idaho,
woody cover and shrub heights were significantly (P<0.01) greater on
sites occupied by pygmy rabbits than on other sites in the same area
[7].


FOOD HABITS : 
The primary food of pygmy rabbits is big sagebrush, which may comprise
up to 99 percent of the food eaten in the winter.  Grasses and forbs are
also eaten from mid- to late summer [2,6,7,8].  In Idaho, Gates and Eng
[6] found that shrubs contributed 85.2 percent (unweighted mean) of
pygmy rabbit diets from July to December.  Shrub use was lowest in
August (73.1%) and highest in December (97.9%).  Big sagebrush was the
most important shrub in the July to December diet (54.2%), followed by
rubber rabbitbrush (Chrysothamnus nauseosus) (25.8%) and winterfat
(Krascheninnikovia lananta) (4.6%).  Grasses comprised 10 percent of the
July to December diet and were consumed mostly during July and August.
Indian ricegrass (Oryzopsis hymenoides) and needlegrass (Stipa spp.)
were the most important grasses consumed.  Forbs contributed 4.9 percent
of the July to December diet [6].

In southeastern Idaho, Green and Flinders [7] found that pygmy rabbits
ate big sagebrush throughout the year but in lesser amounts in summer
(51% of diet) than in winter (99% of diet).  Other shrubs in the area
were consumed infrequently.  Grass and forb consumption was relatively
constant throughout the summer (39% and 10% of diet respectively) and
decreased to a trace amount through fall and winter.  Thickspike
wheatgrass, bluebunch wheatgrass (Pseudoroegneria spicata), and Sandberg
bluegrass were preferred foods in the summer [7].


PREDATORS : 
Weasels (Mustela spp.) are the principal predators of pygmy rabbits.
Coyote (Canis latrans), red fox (Vulpes vulpes), badger, bobcat (Felis
rufus), great horned owl (Bubo virginianus) and marsh hawk (Circus
cyaneus) also prey on pygmy rabbits [2,8,20].


MANAGEMENT CONSIDERATIONS : 
Some populations of pygmy rabbits are susceptible to rapid declines and
possibly local extirpation.  Some studies suggest that pygmy rabbits are
a "high inertia" species with low capacity for rapid increase in density
[17].  The loss of habitat is probably the most significant factor
contributing to pygmy rabbit population declines.  Sagebrush cover is
critical to pygmy rabbits and sagebrush eradication is detrimental [10].
Protection of sagebrush, particularly on floodplains and where high
water tables allow growth of tall, dense stands, is vital to the
survival of pygmy rabbits [4].  Fragmentation of sagebrush communities
also poses a threat to populations of pygmy rabbits [17] because
dispersal potential is limited.


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Brachylagus idahoensis | Pygmy Rabbit