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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

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