| kangapoo rat Temporal range: Late Pliocene - Recent |
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|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Rodentia |
| Family: | Heteromyidae |
| Subfamily: | Dipodomyinae |
| Genus: | Dipodomys Gray, 1841 |
| Species | |
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Dipodomys agilis |
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Kangaroo rats, genus Dipodomys, are small rodents native to North America. The common name derives from their bipedal form: as they hop in a manner similar to the much larger kangaroo, although they are not related. It has been noted that they are not properly characterized as "rats" at all.
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Kangaroo rats are six-toed endotherms with large hind legs, small front legs and relatively large heads. Adults typically weigh between 70-170 g.[1] The tails of kangaroo rats are longer than both their bodies and their heads. Another notable feature of kangaroo rats are their fur lined cheek pouches which are used for storing food. The coloration of kangaroo rats varies from cinnamon buff to dark gray, depending on the species.[2] There is also some variation in length with one of the largest species, the Banner-tail kangaroo rat being six inches in body length and a tail length of eight inches.[2] Sexual dimorphism exists in all species, with males being larger than females.
Kangaroo rats stay in one place bipedally. The Merriam kangaroo rat can leap 7-8 feet and quickly change its direction when landing. The Banner-tailed kangaroo rat can move rapidly which minimizes energy costs and predation risks.[3] It will also go into a “move- freeze” mode which may reduce predation at night.
Kangaroo rats live in arid and semi-arid areas particularly on sandy or soft soils[2] which are suitable for burrowing. They can, however, vary in both geographic range and habitat. In particular, the Merriam kangaroo rat ranges though Southern California, Utah, Southwest New Mexico, Arizona, and northern Mexico and live in areas of low rainfall and humidity, and high summer temperature and evaporation rates.[4] They can be found in areas of various elevations ranging from below sea level to about 4500 feet.[4] The Merriam kangaroo rat lives in stony soils including clays gravel and rocks, which is harder than soils preferred by some other species like the Banner-tail kangaroo rat.[2] Merriam kangaroo rats live in hot and dry areas, conserve water, and only use metabolic sources.[5] They survive by breaking down of the seeds they eat with their metabolism and not needing to drink water. They can also conserve water by lowering their metabolic rate, which reduces loss of water through their skin and respiratory system.[5]
The Banner-tailed kangaroo rat ranges from Northeastern Arizona southward to Aguascalientes and San Luis Posi, Mexico and from Arizona to Western Texas. They generally live in grasslands and scrublands. Banner-tailed kangaroo rats live in dry areas but have more water available to them than Merriam kangaroo rats. All kangaroo rat species are sensitive to extreme temperatures and remain in their burrows during rain storms and other forms of inclement weather.[2] Kangaroo rats are preyed on by coyotes, foxes, badgers, weasels, owls, and snakes.
Kangaroo rats are primarily seed eaters.[6] They will, however, sometimes eat vegetation at certain times of the year and some insects.[2] They have been observed storing the seeds of mesquite, creosote, bush, purslane, ocotillo and grama grass in their cheek pouches. Kangaroo rat will store extra seeds in seed caches.[4] This caching behavior has an impact on the rangeland and croplands where the animals live.[2] Kangaroo rats must harvest as much seeds as possible in as little time as possible.[6] They need to decrease the time away from their burrows as they are cool and dry. In addition, being away from their burrows also makes them vulnerable to predators.[6]
When on foraging trips, kangaroo rats hoard the seeds that they find. It is important for a kangaroo rat to encounter more food items than are consumed, at least at one point in the year, as well as defend or rediscover food caches and remain within the same areas long enough to utilize food resources.[3] Different species of kangaroo rat may have different seed caching strategies to coexist with each other, as is the case for the Banner-tailed kangaroo rat and the Merriam kangaroo rat which have overlapping ranges.[1] Merriam kangaroo rats scatterhoards small clumps of seeds in many small holes.[7] This is done close to the burrow and travel costs are minimized and harvest rates are maximized.[7] Banner-tailed kangaroo rats larderhoard on large mounds.[7] This could give them extra time and energy and decrease the risk of predation. They also spend less time on the surface digging small caches.
Kangaroo rats inhabit overlapping home ranges. These home ranges tend to be small with much activities within 200-300 ft and rarely 600 ft.[2] Home range size can vary within species with Merriam kangaroo rats having larger home ranges than Banner-tailed kangaroo rats. Recently weaned kangaroo rats move into new areas not occupied by adults. Within its home range, a kangaroo has a defended territory consisting of its burrowing system.
Kangaroo rats live in complex burrow systems. The burrows have separate chambers for specific proposes like sleeping, living and food storage.[2] The spacing of the burrows depends on the number of kangaroo rats and the abundance of food. Kangaroo rats also live in colonies that range from six to several hundred dens.[4] The burrow of a kangaroo rat is important in providing protection from the harsh desert environment. To maintain a constant temperature and relative humidity in their burrows, kangaroo rats plug the entrances with soil during the day.[2] When the outside temperature is too hot, a kangaroo rat stays in its cool, humid burrow and leaves it only at night.[5] To provide large amounts of moisture through respiration when sleeping, a kangaroo rat buries its nose in its fur to accumulate a small pocket of moist air.[5] The burrows of Merriam kangaroo rats are simpler and shallower than those of Banner-tailed kangaroo rats. Banner-tailed kangaroo rats also mate in their burrows, unlike Merriam kangaroo rats.
Kangaroo rats are generally solitary animals with little to no social organization. Kangaroos rats do sometime cluster together in some feeding situations. Groups of kangaroo rats that do exist are aggregations and colonies.[2] There appears to be a dominance hierarchy among kangaroo rats with males competing for access to females.[8] Male kangaroo rats are generally more aggressive than females and are more dominant over them. Females are more tolerant of each other than males are and have more non-aggressive interactions. This is likely become the home ranges of females overlap less than the home ranges of males.[8] There appears to be linear dominance hierarchies among males but it is not known if this is the case for females.[8] Winners of aggressive encounters appear to be the most active ones.
Kangaroo rats have a promiscuous mating system. Their reproductive output is highest in summer following high rainfalls.[9]