BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Perognathus parvus | Great Basin Pocket Mouse 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
In late fall and winter, Great Basin pocket mice remain in their burrows
in a state of torpor [33,34].  They emerge from their burrows and mate
in early spring [33,34,43].  Males emerge slightly before females.  In
south-central Washington, Great Basin pocket mice emerged from March to
April [23].  Prebreeding enlargement of ovaries and testes begins in
winter in the complete darkness of the burrow.  Following emergence from
the burrow, the lengthening photoperiod of spring apparently triggers
final enlargement and development of gonads for breeding [27].  Access
to succulent green vegetation in spring may enhance reproductive success
of females.  Captive female Great Basin pocket mice from eastern
Washingon fed lettuce and seeds had significantly larger ovaries than
control females fed only seeds.  Great Basin pocket mice remain
reproductively active through summer.  Females produce one or two
litters per year.  Most first litters are delivered in May and second
litters in August [38,43].  Reports of average litter size have ranged
from 3.9 in south-central Washington [38] to 5.6 in Nevada [20].
First-litter subadults first leave the natal burrow in early summer;
subadults from the second litter first emerge in fall.  In a 2-year
study in south-central Washington, first-litter subadults first emerged
in June, and second-litter subadults first emerged in October (1974) and
November (1975) [23].

As it signals the beginning of the breeding season, photoperiod may
often signal its end.  In the laboratory, an artificial short day-long
night summer photoperiod caused gonadal shrinkage in Great Basin pocket
mice.  A favorable diet apparently overrides this effect, however,
extending the breeding season.  In nature, Great Basin pocket mice
remain reproductively active through fall in years of favorable plant
production.  Juveniles typically breed in their second year, but
first-litter individuals may first reach breeding condition before
winter when plant productivity is high [27].


PREFERRED HABITAT : 
Great Basin pocket mice occupy open, arid terrain.  They seek friable
soil of a variety of textures for burrowing [5,22,42].

Home ranges of 7,060 to 9,630 square feet (656-895 sq m) have been
reported for Great Basin pocket mice in British Columbia.  Males may
have larger home ranges than females.  Average home ranges reported from
south-central Washington are 23,030 square feet (2,140 sq m) and 33,640
square feet (3,125 sq m) for adult males and 15,564 square feet (1,446
sq m) for adult females [38].  In big sagebrush habitat on the Malheur
National Wildlife Refuge, Oregon, home ranges of adult males were
significantly greater (p < 0.001) than home ranges of females.
Reproductively active adult males had significantly (p < 0.05) larger
home ranges than adult males with unenlarged testes.  In black
greasewood (Sarcobatus vermiculatus) habitat, however, there were no
significant differences between male and female home ranges or between
home ranges of reproductive and nonreproductive adult males [14].


COVER REQUIREMENTS : 
Great Basin pocket mice are nocturnal and use burrows for daytime cover.
They also use burrows during periods of winter and summer torpor
[30,32,38,43].  The winter burrow consists of a 3- to 6-foot- (0.9-1.8 m-)
deep tunnel leading to a chamber lined with dry vegetation.  The
summer burrow is shallow.  Except for mothers with young, the burrow is
occupied by a single individual [43].


FOOD HABITS : 
Great Basin pocket mice consume primarily seeds, but eat some green
vegetation [33,34].  Prior to production of seeds, they also consume
insects [11].  Great Basin pocket mice do not use free water [36]; they
metabolize water from food [43].  Pocket mice (Perognathus spp.) and
other heteromyids are scatterhoarders:  They cache seeds in shallow
depressions and cover the seeds with soil.  The seeds are primarily
those of grass species, and some preferred forb species.  Indian
ricegrass (Oryzopsis hymenoides) [29], cheatgrass (Bromus tectorum),
Russian-thistle (Salsola kali), [38], antelope bitterbrush (Purshia
tridentata) [16,43], pigweed (Amaranthus spp.), and mustard (Brassica
spp.) [43] seeds are important Great Basin pocket mouse food items.  In
productive years, cheatgrass seeds formed a major portion of the diet of
Great Basin pocket mice in southeastern Washington [38].

Seeds of medusahead (Taeniatherum caput-medusae) were not used by Great
Basin pocket mice in Lassen County, California, and areas with heavy
medusahead invasion were avoided [29].

Estimated seed intake of a Great Basin pocket mouse is from 4 to 10
percent of total body weight daily.  Assuming a wholly cheatgrass diet,
an individual requires 870 to 1,000 seeds per day in spring and summer,
and about 750 seeds per day in fall.  Estimated daily maintenance energy
requirement ranges from a winter low of 2.4 kilocalories (males) and 2.6
kilocalories (females) to a high of 7.0 kilocalories (males) and 6.6
kilocalories (females) in spring.  A total of about 1.8 to 2.1 ounces
(50-60 g) of seed must be cached to meet the winter energy requirement
[38].  To conserve energy when food is scarce in summer, Great Basin
pocket mice often enter a state of torpor that lasts a few hours
[23,38].

Great Basin pocket mice are fairly successful at finding buried seed
caches, even those buried by other individuals.  In a laboratory
experiment, Great Basin pocket mice found Indian ricegrass seeds 17.5
percent of the time when researchers cached seeds 1.3 centimeters below
ground; 42.5 percent of the time when seeds were cached 0.6 centimeter
below ground; and 100 percent of the time when seeds were scattered on
the soil surface [25].  


PREDATORS : 
Owls (Tytonidae and Strigidae) [43], including northern saw-whet owls
(Aegolius acadicus) [8] and burrowing owls (Speotyto cunicularia) [24],
hawks (Accipitridae) [43], coyotes (Canis latrans) [12,40], foxes (Vulpes
and Urocyon spp.), weasels and skunks (Mustelidae), and snakes
(Serpentes) [43] prey on Great Basin pocket mice.


MANAGEMENT CONSIDERATIONS : 
As scatterhoarders, Great Basin pocket mice and other heteromyids have
great ecological importance.  Some native desert plant species including
Indian ricegrass, antelope bitterbrush, and palo verde (Cercidium
microphyllum) have no seed appendanges to facilitate dispersal, and
apparently require heteromyids for seed dispersal [29].  Many seed
caches of these granivores are not consumed, and unconsumed seed in
caches has a greater probability of germinating and establishing than
does uncached seed.  McAdoo and Klebenow [32] found that Indian
ricegrass seeds from scatterhoards often had 100 percent germination.
This is probably because only seeds with filled seedcoats were cached,
and because seedcoats are often cracked and embryos germinate more
easily when seeds are handled by heteromyids.  Furthermore,
scatterhoards are not vulnerable to bird and ant granivores [29].

Schreiber [38] concluded that Great Basin pocket mice probably do not
reduce cheatgrass importance in southeastern Washington even though they
consume large numbers of cheatgrass seeds.  Surviving cheatgrass plants
have reduced competition for soil nutrients and water, and respond with
increased seed production.

Disturbance tends to favor Great Basin pocket mice, especially when the
disturbance favors growth of herbaceous species.  In Oregon, Great Basin
pocket mouse populations were greater in logged than in unlogged forest
[4].  In southern Utah, populations were larger in pinyon-juniper
(Pinus-Juniperus spp.) chained and seeded to grasses than in untreated
pinyon-juniper [1].  Grass seeding attracts Great Basin pocket mice to
scattered seed and later, to new herbaceous growth [2].

Light- to moderate-intensity livestock grazing apparently does not
reduce Great Basin pocket mouse numbers.  In Nevada, populations were
actually larger in riparian zones grazed by cattle than in ungrazed
riparian zones [9].  In northwestern Nevada, Oldemeyer and Allen-Johnson
[35] found no significant differences between in Great Basin pocket
mouse abundance on ungrazed sites and on an allotment subjected to
a light-to-moderate-use deferred grazing system.


REFERENCES : 

Related categories for Wildlife Species: Perognathus parvus | Great Basin Pocket Mouse