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Heermann's kangaroo rat
Heermann's kangaroo rat, Dipodomys heermanni, is found
exclusively in the state of California. The northern boundary of the
species can be defined by a line connecting Suisun Bay to Lake
Tahoe. The range extends south for roughly 500 kilometers to Point
Conception in Santa Barbara Co. Dipodomys heermanni occurs widely
throughout the central portion of the state, and extends westward to
the coast at some points. While found in a variety of habitats,
Heermann's kangaroo rat is limited to elevations of 3000 feet and
below.
Heermann's kangaroo rat is found in a great diversity of habitats.
Some of the subspecies prefer the plains of the central California
coast, some inhabit sandy valley bottoms, and some are more likely
to be found on hilly knolls with shallow soils. These habitats
extend from the foothills of the Sierra Nevada to the interior and
coastal valleys.
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Heermann's kangaroo rat
Heermann's kangaroo rat ranges in size from 250 to 313 mm in length,
with the tail averaging 180 mm in length. It has a long tufted tail,
long hind feet/limbs, short forefeet, dorsal color varying from
tawny brown to buff, and a white stripe running along the upper
thigh. The hip stripe is conspicuously absent in the subspecies D.
h. morroensis. Dipodomys heermanni has 5 toes on the hind foot, and
is a member of the "broad-faced" kangaroo rat group. The combination
of five toes and broad face distinguish D. heermanni from all other
sympatric species of kangaroo rats (except the significantly larger
D. ingens).
Heermann's kangaroo rat is sexually dimorphic in both external and
cranial measurements, with males larger in all cases. TDipodomys heermanni has a secretory gland located between the
shoulders which is thought to play a part in scent communication or
pelage maintenance. The gland does not show seasonal dimorphism in
D. heermanni. Variation in tail and body color, among other
characters, helps to differentiate the nine recognized subspecies.
Reproduction
Heermann's kangaroo rat breeds from February to October. Breeding
peaks in April. The gestation period lasts 31 days, with litters of
up to 6 pups being produced. Average litter size has been reported
to range from 2.6 to 3.7. The newborn kangaroo rat is mostly
hairless, and the eyes and outer ears are closed. The cheek pouches
at this stage are simple folds. By day 3, the young rat is able to
crawl and begins to grow dorsal and cranial hairs. It has skin
pigmentation that matches adult pelage patterns. By day 9, the sex
of the rat can be determined by checking for swellings in the
genital area (swellings are present in males, absent in females). By
day 14 the kangaroo rat pup can stand, and achieves bipedality by
day 20. The weaning process begins in the third week and is
completed by day 25. Sexual maturity is achieved at some point past
the third week; in congenerics of D. heermanni, maturity was
achieved at times ranging from day 32 to day 56. Foraging begins at
4 weeks, adult weight is reached at 2.5-4 months, and the molt to
adult pelage is complete by the fifth month.
Behavior
Heermann's kangaroo rat is a nocturnal, solitary species and lives
in a nest burrow. Depending on the soil composition, the burrows
leading to the nest may be complex with many twists and turns, or
may be a simple tunnel of relatively shallow depth. Increasing soil
sandiness and shallowness is correlated with decreasing burrow
complexity. The rat may spend up to 23 hours a day in the burrow.
Foraging for food takes place along defined runways. Dipodomys
heermanni tends to leave the burrow very soon after dark, but it
will avoid going outside when bright moonlight is present. The rat
can reach a top speed of 5 meters/second. Dust bathing is a common
activity after foraging. This is necessary to keep the pelage and
skin in good condition. When the rat is denied the opportunity to
dust-bathe, the fur mats up and sores may appear on the rat's back.
Heermann's kangaroo rat does not seem to vocalize in the field, and
very few noises have been heard in the lab. The rat does "footdrum",
however, by beating the hindfeet against the ground. This
footdrumming is sometimes aimed at predators, specifically snakes.
The purpose seems to be to show the predator that the rat is aware
of the threat. Kangaroo rats may also footdrum in order to advertise
their presence within a territory.
Heermann's kangaroo rat is a solitary animal, and shows high levels
of aggression to conspecifics in captivity. Even when females are at
the height of estrus, aggression levels (for both sexes) are high
and can sometimes be fatal.
Food Habits
Heermann's kangaroo rat feeds on a variety of plant species. Grasses
are eaten as the kangaroo rat forages on the ground surface, while
seeds are stored in the cheek pouches and taken home to the burrow
for storage and later consumption. Dipodomys heermanni feeds on
different plants as seasons change. In spring, Erodium species are
the prominent source of food. In the dry season, Bromus mollis is
taken most frequently, while Eromocarpus is the favored food in
fall. With the onset of winter, Erodium becomes the primary food
source once again. The kangaroo rat will also feed on insects such
as moths, beetles, and grasshoppers.
In captivity they should be offered a complete diet of lab blocks, and rat or mouse
mix, with bits of fruit or veggies regularly. Cheerios or wheat
bread are great treats, in small quantities. Do NOT feed chocolate,
fried foods, salted foods, candy or junk food! They may enjoy
crickets and mealworms if they are captive bred, never feed wild
insects as they may carry parasites. Vitamins, like Nutri-Cal are a good addition to their diet, and added calcium
during nursing and growth due to demands on their systems at those
times, but take care not to overdo it. Water bottles should be used
to proved constant, clean water. Ceramic or stoneware food dishes
work well for keeping seeds or fresh foods off the floor, and a wire
mesh hopper that allows them to eat the lab blocks through without
extra waste.
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