The kangaroo rats are a set of species of rodents belonging to the genus Dipodomys. These animals are characterized by having very developed hind legs and large in size with respect to the rest of their body, which allows them to move in a bipedal way, similar to the locomotion of kangaroos..
Although this characteristic is also found in the Australian kangaroo rat (or furious rat) of the genus Notomys, these genera are not related. The similarities between these animals are due to a convergent evolution, in response to their adaptation to similar environments.
Kangaroo rats have undergone a series of physiological adaptations that allow them to survive arid climates with a shortage of water. It is for this reason that most species of Dipodomys do not consume a significant amount of water, as they are capable of obtaining it through metabolic processes (oxidative phosphorylation).
The gender Dipodomys occupies arid and semi-arid regions of western North America, although some species are more associated with green habitats such as prairies and grasslands.
They can be found from southern Canada to Mexico, where they have a wide distribution. These animals reside in burrows with a complex system of cameras and tunnels..
Kangaroo rats are predominantly granivorous, and often forage in open spaces between evergreen shrubs. In addition, they are generally nocturnal and twilight..
Kangaroo rats have a prominent body, with moderately spaced ears about 15 millimeters apart. Their eyes are large and have long whiskers that function as motion sensors. Like other rodents, Diponomys It has a kind of pockets on the cheeks that allow them to store and move food.
The skull of Dipodomys It is triangular, the occiput being the base of the triangle, and the tip of the nose the apex of it. In the middle ear they present flattened auditory tubes and the mastoid antrum particularly inflated.
The front limbs are short and weak. On the other hand, the hind legs are very strong and large, with four well-developed toes. The tail is very long, about 40% longer than the body.
On Dipodomys, the dorsal color is generally yellowish brown, although in some species there are light, grayish tones with black touches. On the hips they have white stripes.
The tail exhibits blackish or brown tones in the dorsal and ventral areas, which darken towards the distal portion. Towards the middle of the tail there are two light lateral stripes, and the tip is white from about 4 centimeters to the end.
On the lower portion of the body there are hairs with white bases and leaden tones. Towards the base of the tail the fur turns yellowish.
The front legs are completely white while on the back legs there are hairs with gray bases that turn blackish towards the ankles. The hind legs are white on the dorsal area and dark brown to black on the underside..
Generally, the coloration of kangaroo rats remains stable, although in juveniles there are more grayish tones than brown. These animals usually shed their fur in autumn, showing a brighter and brownish coloration during fall, winter and spring, and duller in summer..
In kangaroo rats, a sebaceous gland is found in the middle of the back. This gland is located approximately one third of the distance between the ears and the rump and has an elliptical shape with around nine millimeters in length..
The appearance of this gland is rough and granular and on it the growth of fur is much less, which allows it to be easily located and even visible from above when the fur is worn, just before the molt..
This gland secretes oil on the coat, allowing kangaroo rats to preserve their skin and hair in a healthy way in the arid and sandy environment in which they live..
Kangaroo rat measurements do not differ significantly between non-pregnant males and females, although males are slightly heavier.
In general, they have a total length (from the nose to the tip of the tail) of approximately 32.6 centimeters. The tail, from the base to the tip, measures around 18.8 centimeters, and the hind legs are up to 5 centimeters.
The weight in females is around 113 grams, while males can weigh up to 120 grams.
There are 20 species described for the genus Dipodomys. Although 22 species were previously counted, two of these (D. insularis Y D. margaritae) were reduced to subspecies of Dipodomys merriami.
The variation in coloration among most species consists of slight changes in the length of the white color at the tip of the tail and the shades of the coat, although the pattern is maintained in most of these..
Kangaroo rats generally feed on seeds of different plant species such as the sweet mosque (Prosopis glandulosa). They can also ingest green parts of some plants and on some occasions some individuals have been recorded consuming insects.
The quantity and proportion of food items varies somewhat between species. One of the most studied kangaroo rat species is D. merriami. In these animals, the largest proportion of food is seeds. These rats are able to survive on seeds without water.
However, between the months of February to May and August, the green parts of the plants represent up to 30% of the stomach content of D. merriami. It is estimated that these items are used as sources of water in the reproductive periods..
On the other hand, D. microps It is a species that has specialized in the consumption of leaves from the bush Atriplex confertitolia. This peculiar plant accumulates more electrolytes in its leaves than other plant species present in the same habitat.
These electrolytes allow maintaining the water balance of these plants, and likewise, they give them the quality of conserving between 50 and 80% water in their leaves..
This unique adaptation in the diet of D. microps It may also be due to a decrease in competition for seeds between the different species of kangaroo rats that live in the same locality..
Kangaroo rat adults have several reproductive periods in the year. During this period, reproductive males are recognized as having an enlarged abdomen and testicles to about 5 millimeters..
In kind D. merriami It has been recorded that, in the months between February and September, up to 50% of males are sexually active. On the other hand, females show a peak of reproductive activity between the months of January and August. The species D. spectabilis shows the same breeding season, which runs from January to the end of August.
These animals are polygamous, which indicates that females and males reproduce with several pairs in each reproductive phase. In some species, courtship consists of mutually sniffing each other's anus, until the female allows the male to mount her. In other species, short chases and grooming are carried out.
The gestational period varies between 20 to 30 days, depending on the species. Females give birth to their young in chambers built into burrows. These pups are born without hair and with very little developed eyesight..
Between their first 10 and 15 days, they have already developed their sight and are covered by a thin layer of hair. After three to four weeks, the juveniles are almost fully developed and become independent.
Kangaroo rats are usually solitary and a bit territorial. For this reason, when an individual invades the territory of another, this one actively attacks it, although these fights are short and consist mainly of hitting the hind legs in the air. On the other hand, these animals are shy in the presence of humans.
The greater interaction that individuals from Dipodomys takes place in the reproductive periods. There is usually a certain degree of dominance among males, although females lack any hierarchical order.
As in other nocturnal animals, in Dipodomys there has been a change in the activity pattern related to the different lunar phases.
In such a way that, in the full moon phase, animals avoid open spaces and stay close to their burrows longer at night, going out to look for food only during twilight hours (dusk and dawn).
It is believed that this behavior occurs to avoid nocturnal predators, exposing less to them on clearer nights.
Kangaroo rats generally inhabit semi-arid areas in temperate deserts and many of the species share these territories. However, temperate scrubs are also used by these animals, and up to 12 species can be found in these areas..
Another habitat frequently used by Dipodomys It is the prairie, where it is common for them to build their burrows under bushes.
Temperate forests and dry savannas are territories where some species of kangaroo rats can also be found, such as the giant rat D. ingens. This species usually inhabits plains in the foothills and areas with shrubs and perennial grasses.
The extreme desert is used by D. gravipes, D. phillipsii Y D. merriami. Due to the replacement of the natural ecosystems of these species, it is common for them to inhabit artificial grasslands and some crops. Some rocky areas like cliffs, are rarely used by D. microps.
The gender Dipodomys It is found in western North America and can be found from Canada to much of Mexico. In Canada species have been recorded in Vancouver and Calgary.
The United States has records from the north of the country, through Dakota and Seattle, to California, Arizona and New Mexico to the south.
In Mexico they are found from Chihuahua to San Luis Potosí, with some populations found on the coast of Tijuana, Hermosillo and Culiacán.
Kangaroo rats, like other animals that live in areas with little water availability, have developed characteristics that allow them to conserve body water very effectively.
Some species of Dipodomys ingest water from the medium, being able to consume up to 10 to 12 milliliters of water per day, as is the case with Dipodomys ordii columbianus. On the other hand, Dipodomys merriami does not consume water, as it is able to obtain it from the seeds on which it feeds.
In these animals, the structures of the kidneys located in the medulla of the same, known as loops of Henle, are highly developed. These structures have descending and ascending tubules or branches, up to four times longer than in the case of humans..
In this way, the tubular fluids in the kidney are very close to osmotic equilibrium with the interstitial fluid. This occurs due to the efficient reabsorption of water through the tubules of the loop of Henle during the urine production process..
This reabsorption process causes the production of urine with a high concentration, of more than 6000 mosmol / KgHtwoOR.
The species of the genus Dipodomys that inhabit extreme arid environments, they are able to conserve the metabolic water produced from oxidative phosphorylation, reducing their metabolic and respiration rates. This explains the low activity of these animals, which spend most of the day in the cool, humid chambers of their burrows..
Several studies have shown that when these animals are subjected to a diet with little water availability, the respiratory rate drops from an average of 93.7 breaths per minute to between 44 and 53 breaths per minute. In this way, the loss of water through steam in respiration is reduced..
On the other hand, they prevent the loss of water through the integument, thanks to an oil gland that protects their fur and skin from heat and desiccation, thus reducing the activity of the sweat glands..
Within the genre Dipodomys, 14 of the 20 species described, (70% of the species) are in the category of “least concern” (LC).
The species D. stephensi, D. nitratoides Y D. elator are considered vulnerable (VU), while D. spectabilis is near threatened (NT), D. ingens is considered endangered (EN) and D. gravipes It is the most threatened species, considered critically endangered (CR) according to the IUCN.
Although the population trend in general is increasing, some populations tend to decrease mainly due to the displacement of their habitat..
The development of agriculture has produced various problems for kangaroo rats. Some species turn out to be very sensitive to ecosystem modifications, being seriously affected by crops and crops that have replaced their natural habitats..
It is presumed that the species D. gravipes, that used to inhabit western Baja California, is extinct in nature, due to the almost total reduction of its habitat, due to the establishment of agriculture in said area.
On the other hand, the agricultural industry has exercised a strong control over rodents, as a measure of protection of crops and harvest. These measures have caused large population declines in species such as D. stephensi Y D. elator.