Food Habits
Great Basin pocket mice consume primarily seeds, but eat some green vegetation. Prior to production of seeds, they also consume insects. Great Basin pocket mice do not use free water, they metabolize water from food. Pocket mice (Perognathus spp.) and other heteromyids are scatterhoarders, caching seeds in shallow depressions and covering the seeds with soil. The seeds are primarily those of grass species, and some preferred forb species. Indian ricegrass (Oryzopsis hymenoides), cheatgrass (Bromus tectorum), Russian-thistle (Salsola kali), antelope bitterbrush (Purshia tridentata), pigweed (Amaranthus spp.), and mustard (Brassica spp.) 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.
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.
Estimated seed intake of a Great Basin pocket mouse is from 4% to 10% 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. To conserve energy when food is scarce in summer, Great Basin pocket mice often enter a state of torpor that lasts a few hours.
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% of the time when researchers cached seeds 1.3 centimeters below ground; 42.5% of the time when seeds were cached 0.6 centimeter below ground; and 100% of the time when seeds were scattered on the soil surface.
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