Dipodomys ingens

Geographic Range

Giant kangaroo rats ( Dipodomys ingens ) live in the Nearctic realm and are endemic to California in the United States. Their range extends from the San Joaquin Valley to western nearby valleys. They are spread across six distinct disjunct counties: San Benito, San Luis Obispo, Kings, Kern, Fresno, and Santa Barbara. In San Luis Obispo County, they inhabit several valleys, including San Juan Creek Valley, Cuyama Valley and Carrizo Plain.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Giant kangaroo rats inhabit savannas or grasslands at elevations between 90 to 885 meters, although most populations are at reported elevations of about 200 m. They are commonly found in dry valleys or flat plateaus. They inhabit areas with dry soil for easier digging. Because of the hot and dry conditions that are found in these areas they dig burrows; the burrows provide cooler conditions than the ambient temperatures. Historically, the rats were located in grasslands with perennial species and shrubs called saltbush ( Atriplex ). Currently, they inhabit locations with non-native annual grasses, although it is not the most ideal habitat. During the springtime, vegetation growth increases therefore the rats trim and manicure the vegetation surrounding the burrows to maintain a traversable environment.

They are more commonly documented in grasslands with less than 9% slope – oftentimes much less than this upper limit. Twenty-two percent of the rat population is found on slopes that lack vegetation, resulting in deterioration of land by livestock.

• Habitat Regions
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

Physical Description

Giant kangaroo rats have relatively large back limbs and shorter forelimbs. Their heads are relatively large compared to their bodies. Their tail is longer than their body length. Like all mammals, these rats exhibit bilateral symmetry and are endothermic. These rats also have external cheek pouches.

Male kangaroo rats are slightly larger than females. Males have an average mass of 157g (range 140.0 g to 174.2 g) and females have an average mass of 151.4 g (range 130.8 g to 180.0 g). Males have an average total length of 334.4 mm while females have an average total length of 332.9 mm (range 311 to 348 mm). The kangaroo rats have an average tail length that is 128% the length of their head and body. Their hind foot length averages 47 mm and they have an ear length range of 6.2 to 6.4 mm.

All adults have a brown or tan coat color on the dorsal part of their bodies with a white coat on the ventral side, and visible vibrissae. Their tail tuft is bicolored, brown on dorsal side and white on ventral side and dark compared to their body color; they also have dark stripes running longitudinally from head to tail. The rats’ flanks are usually darker compared to the tan dorsum. Juveniles tend to have paler dorsal coats than adults.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Development

Giant kangaroo rats are born in litters of three to six pups. They are taken care of by female giant kangaroo rats until weaning, which is at about four weeks. Once the young reach a weight of 50 to 70 grams, they leave burrows and are independent. Females reach sexual maturity at about twelve to thirteen weeks, there is no research about males.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

Giant kangaroo rats are likely polygynandrous and reproduce year-round. Female giant kangaroo rats choose neighboring males to mate, as familiarity (of scent) plays a big factor in their sexual interactions. Female giant kangaroo rats allow neighboring males to court them by allowing them to go into their burrows and leave their scent; sometimes males sneak into the burrows to do so. If the females reject the males (likely due to size or pelage color) females will push the males out of their territory. There is male-to-male competition for mating; the males will try and chase other males away.

Mating can be aggressive or nonaggressive. Nonaggressive behaviors include using nose-to-nose or nose-to-anus contact or males mounting onto the females backs. Males also use foot-drumming and sunbathing as methods of attraction. Aggressive measures include direct male-male attacks. In this scenario, males stand 4 cm apart and chase one another.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

The reproduction season of giant kangaroo rats is January to May, with a gestation period lasting about a month. Research suggests they can reproduce outside of their typical reproduction period if there is sporadic rainfall. Their litter size is from three to six, with an average of four pups per litter. Females tend to mate with the same males throughout their breeding season. Females reach breeding age at about twelve to thirteen weeks. They are iteroparous, meaning they breed multiple times in their lives, and give live birth.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous

Research on giant kangaroo rat parental involvement is limited. As solitary animals, they lack biparental care, males aren't involved in parental care outside of the act of mating. Males tend to kill the pups unless they belong to neighboring females. The pups are taken care of by female giant kangaroo rats until weaning, which is approximately four weeks.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

The lifespan of giant kangaroo rats is likely around 2 years, but some can reach up to 6 years. Giant kangaroo rats are not held in captivity. Limits to lifespan may include predation by San Joaquin Kit foxes ( Vulpes macrotis mutica ), and reduced suitable habitats due to urban and industrial expansions into their habitat, including oil and mineral exploration and road-building.

Behavior

Giant kangaroo rats are terricolous and sedentary individuals. They are fossorial, as they live in their self-dug burrows underground. These animals are assumed to be territorial as females chase males away or males chasing other males out of their territory. Giant kangaroo rats are motile and assumed to be diurnal, active during the day; they will leave their burrows at night if there is rain, snow, or if the moonlight is bright.

Males will travel to neighboring female burrows when they are ready to mate. Males tend to follow females into their burrows while maintaining naso-anal contact. Their mating behavior varies with population density. If there are sufficient females in an area then the males won’t travel to other places. Unless mating, they tend to be solitary creatures, staying in their individual burrow systems from 1 to 3 days at a time. During the winter months, these kangaroo rats stay in their burrow systems longer, 1 to 6 days. This is because the weather is too cold for them to scavenge like they usually do in warmer weather.

• Key Behaviors
• terricolous
• fossorial fossorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial

Home Range

Giant kangaroo rats have a home range size of 60 to 350 m^2. The males’ home range changes only when seeking females for mating. Their territory size has not been quantified.

Communication and Perception

Giant kangaroo rats produce vibrations to communicate via foot drumming. They use tactile foot drumming as a way to declare territorial ownership, to prove their dominance over other rats during a competition, to show they're ready to mate, and to alert others of the presence of predators. Giant kangaroo rats use many different techniques to detect and decoy predators. Acoustically, they use their hind legs to drum on the floor and alert other rats of the prey's presence. The rats also employ jump backs to evade predators. They hop backwards in the air creating distance between them and the predator, then they use their hind legs to kick sand towards the predator (a visual and tactile maneuver).

These rats have a strong olfactory sense as well, which helps them tell the difference between familiar and unfamiliar rats using the lipids present on their skin.

Giant kangaroo rats have large eyes and night vision that allow for better navigation in the dark. They see color which helps them notice their environment better. A member of the same genus has been proven to be able to in UV spectrum, although not proven it is likely that the giant kangaroo rat does as well.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• scent marks scent marks
• vibrations vibrations

• Perception Channels
• visual visual
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

Giant kangaroo rats are omnivores (granivores and insectivores). Their diet primarily consists of seeds, but they also eat green plants and insects. They eat the heads of ripe grasses, caching them in an area over their burrow system. These caches include seed pods with scattered seeds mixed in an upper layer of soil. When gathering their seed heads they store them in their cheek pouches and then cache them by burying them. Female rats fill their cheek pouches with green foliage that is vital to their diet when nursing. Juvenile females and adult males typically store grass and green foliage in their cheeks. Among seeds and grasses, some rats store insects such as bees and wasps.

Giant kangaroo rats typically scavenge the ground for food around sunset to sunrise, typically starting 2 hours after sunset. During the spring, the rats forage for seeds more often because the plants are at their ripest. During droughts, the rats depend on the hoarded food they have near their burrows which allows them to survive despite the lack of available resources.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
• herbivore herbivore
  • granivore granivore
• omnivore omnivore

• Animal Foods
• insects

• Plant Foods
• seeds, grains, and nuts

• Foraging Behavior
• stores or caches food stores or caches food

Predation

Giant kangaroo rats use vibrations from the ground to know when there is an incoming predator. They have large auditory cavities that help them hear low-frequency sounds. They use foot-drumming to communicate with their predators. Their main predators are rattlesnakes (Crotalus), gopher snakes ( Pituophis catenifer ), and San Joaquin kit foxes ( Vulpes macrotis mutica ). To successfully escape from their predators, they use gymnastic-like techniques to jump away from them. When rattlesnakes attack, rats' will jump vertically above the snakes or backwards to escape the snakes’ strike. They will also use their hind legs to strike the snakes in the face or throw sand in their faces. Gopher snakes will enter the giant kangaroo rats’ burrows and attack. Rat burrows have multiple entrances for escape routes; once out of the burrow, these kangaroo rats will push substrate into the entrance to trap the snakes.

Ecosystem Roles

Giant kangaroo rats have a diet that consists of seeds, grains, and nuts. They are eaten by snakes and San Joaquin kit foxes ( Vulpes macrotis mutica ). Giant kangaroo rats are parasitized by rodent fleas ( Hoplopsyllus anomalus , Meringis californicus ), and bird fleas ( Echidnopohaga gallinadea ). Fleas can infest their burrow systems. Ticks ( Ixodes ) also parasitize giant kangaroo rats. Harvester ants ( Pogonomyrmex ) and giant kangaroo rats have a mutualistic relationship; ants also use the burrows made by the rats.

• Ecosystem Impact
• creates habitat

Economic Importance for Humans: Positive

Giant kangaroo rats have no reported positive economic impacts on humans.

Economic Importance for Humans: Negative

Giant kangaroo rats have no reported negative economic impacts on humans.

Conservation Status

Giant kangaroo rats is listed as “Endangered” by the IUCN Red List and the federal list. They fall under Appendix I of CITES, which means they cannot be collected or commercially traded. They have no species status on the State of Michigan list.

The rats are threatened by environmental and biological factors. The increase in urbanization has led to habitat loss. Excessive livestock has also impacted the population size of these rats due to them crushing their burrows. Fires and the lack of grazing have caused a loss of vegetation which threatens the survival of the rats. Due to the urbanization of their natural habitat, giant kangaroo rats now occupy only 6 percent of their original home range.

There are some conservation actions in place limiting experimental research on the rats and they also live on conservation sites over many ranges. Giant kangaroo rats and other endangered species, San Joaquin kit foxes ( Vulpes macrotis mutica ) are protected under the San Juaquin Valley recovery plan for upland species. The recovery plan focuses on the protection of their habitat, banning rodenticides, and limits livestock grazing the land. There are efforts to regulate the oil and gas extractions due to giant kangaroo rats dying in the contaminated drainage. There is constant monitoring of their populations.

Additional Links

Encyclopedia of Life

Contributors

Eliany Garcia-Bermudez (author), Radford University, Natalie May (editor), Radford University, Alexander McVicker (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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