The dark kangaroo mouse, also known as Owyhee River kangaroo mouse, is named for its dark-furred back, long hind feet, and the way it moves around by hopping on its hind legs like Australian kangaroos. It belongs to the order Rodentia and Family Heteromyidae. Its head is large in comparison to its body size due to enlarged auditory bullae. It has a relatively short neck large ears, prominent eyes, a long snout, long whiskers and a fat, haired tail. The coat of dark kangaroo mouse is long, silky, and soft with its back being brownish to greyish black while its belly having a greyish or whitish hue. Its tail is swollen in the middle. The fat deposits vary in size as season changes because it is used as a source of energy during dormancy. The tails are thickest before entering winter hibernation and thin in the spring, when they come out of hibernation and assume normal activity. This is unique among North American small mammals. There is no sexual dimorphism shown in dark kangaroo mouse except for zymomatic breadth. Length of hind foot, cranial measurement, and mandibular length vary little while weight is highly variable in the population. The total length ranges from 138 to 177 mm with an average of 160 mm, length of tail: 68–103 mm, hind foot length: 23–27 mm, weight of adults ranges from 10 to 16.9 g with an average of 13.1 g.
Distribution and habitat
The dark kangaroo mouse species is native to the west of United States. They prefer to live in loose sand and gravels. This species is listed as "Least Concern" on the Red List because it is relatively widespread, although there has been a slight reduction in its population due to loss of habitats caused by modern agriculture. Their main predators are owls, foxes, badgers and snakes.
Diet
Dark kangaroo mice mostly eat small seeds, which are carried back to their burrows in their cheek pouches. They also feed on some insects in the summer. This change in diet is suggested to be caused by pocket mice being at its peak activity and competing for food with the dark kangaroo mice. Kangaroo mice do not drink water actively, instead, utilize water from their food source. They also have adaptation mechanisms to further conserve water: being active at night, concentrating their urine, and producing dry feces.
Behavior
Dark kangaroo mice are mostly bipedal which move around by hopping on their two hind legs. Using bipedalism is suggested to be a result of foraging behaviors and using it as a locomotion mode only serves as a side function. They also have been seen to be moving on all 4 limbs when moving in contained spaces such as a cage. These kangaroo mice are nocturnal animal with peak of activity in the first 2 hours after sunset. Their activity is only observed from March through October while they go into hibernation during winter months. These animals are also sensitive to moonlight and temperature. Their activities are decreased when the temperature is out of their optimal range and in presence of moonlight.
