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Desert Kangaroo Rat - Dipodomys deserti
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Desert Kangaroo Rat - Dipodomys deserti

[Image: 0395.jpeg]

Scientific classification
Kingdom:  Animalia
Phylum:  Chordata
Class:  Mammalia
Order:  Rodentia
Family:  Heteromyidae
Genus:  Dipodomys
Species:  Dipodomys deserti  Stephens, 1887

The desert kangaroo rat (Dipodomys deserti) is a rodent species in the family Heteromyidae that is found in desert areas of southwestern North America. It is one of the large kangaroo rats, with a total length greater than 12 inches (30 cm) and a mass greater than 3.2oz (91g).

Range
The desert kangaroo rat is found in arid parts of southwestern North America, including Death Valley, the Great Basin, the Mojave Desert, and portions of the Sonoran Desert. Though kangaroo rats persist in a variety of soils, desert kangaroo rats live exclusively in areas with loose sand, often dune terrain. The places on this list constitute some of the most extreme deserts in the United States including Death Valley, which has the record for the hottest place on the continent.

Habitat
Desert kangaroo rats are denizens of desert areas with sandy soil; vegetation is typically sparse and consists of creosote bush, a variety of grasses, and cacti. Desert kangaroo rats live in burrow systems under slight mounds of soil 6-9m across; they sleep in a den, which is sealed off at extreme temperatures, during the day. Groups of 6-12 widely spaced burrows may constitute a colony of this species, which is otherwise solitary.

Ecology
Foraging ecology

Seeds are the dominant component of the diet of desert kangaroo rats. The size of the seeds consumed by the species tends to be larger than seeds consumed by other, sympatricheteromyids. When presented with patches with variation in seed sizes and densities—which in combination vary total profitability—desert kangaroo rats tend to choose large-seed patches but reduce profitability of a set of patches to similar levels. Seed selection also appears correlated with nutritional content, with this species choosing seeds with high carbohydrate content. Although some kangaroo rats will consume green vegetation, desert kangaroo rats do not. Feeding occurs in fits and starts of movement and at relatively discrete locations, with an average distance of ~7 m (22 ft.) between stops.

Water ecology
Most kangaroo rat species live in arid environments and are known for their ability to make use of metabolic water rather than requiring it from the environment. While the desert kangaroo rats do consume available water, the vast majority of their water requirements are met from byproducts of metabolic processes. Adaptation to very low quantities of water (free or metabolic) is highlighted by the very long water turnover times for the species, on the order of 2–3 weeks.

Special Physiology
Kidneys

Kangaroo rats achieve the ability to be sustained on limited water by having incredibly derived kidneys. To remove waste without losing water, many species have developed mechanisms to concentrate their urine. This happens in the kidneys. There seems to be an inverse correlation of body mass to ability to concentrate urine. So naturally small rodents can persist in much more water deficient environments than larger animals. The desert kangaroo rat has a kidney structure very similar to those of other rodents, but it has much longer papilla (mammalian species). Papilla lengths, along with number of nephrons, play a crucial role in urine concentration.

Skull Anatomy
Desert kangaroo rats have the longest nasal cavity of all the kangaroo rats, which allows for better water conservation. Hot, dry air can remove water from the body. The long nasal cavities reduce this water loss by cooling the air leaving the lungs. Cooling air releases moisture for reabsorption to the body so its loss can be avoided in a situation where water is a precious resource.

Group Interaction
Foot Drumming

Kangaroo rats drum their feet. Many different species of kangaroo rats' drumming pattern have been previously studied. They are thought to have evolved independently. Some use drumming to communicate location and other kangaroo rats respond in kind. This is not the case with the desert kangaroo rat. The desert kangaroo rat, living in a sand dune environment, has the highest level of food scarcity. When the desert kangaroo rat hears a drum from another rat, it comes out of its burrow and chases it away or engages in a rollover fight.

Predation

Desert kangaroo rats function under a high risk of predation for a variety of reasons. The first of which is they forage alone. They do not have a community of other rats to watch out for snakes or other predators. Secondly, in the desert, food is scarce and spread out, so desert rodents have to spend a substantial amount of time out of their holes searching for food. Because of these reasons, the desert kangaroo rat has had to evolve a few adaptations to protect itself.

Snakes
Though the more commonly studied Merriam's kangaroo rat protects itself by predator avoidance, the desert kangaroo rat behaves more aggressively. In the case of a snake, the desert kangaroo rat drums its feet and moves within striking distance of the snake and kicks sand in the air. Though this is an incredibly dangerous activity for a small rodent, it does these things to let the snake know it is alert to its presence. Snakes are less likely to attack a rodent if the prey knows the snake is there. Desert kangaroo rats exclusively kick sand due to their natural environment being characterized by loose sand dunes.



High-speed videos capture how kangaroo rat escapes rattlesnake attack

March 27, 2019, University of California - Riverside

Kangaroo rats are abundant and seemingly defenseless seed-eating rodents that have to contend with a host of nasty predators, including rattlesnakes—venomous pit vipers well known for their deadly, lightning-quick strikes.

Research by a student-led team from UC Riverside, San Diego State University, and UC Davis now shows that desert kangaroo rats frequently foil snakes through a combination of fast reaction times, powerful evasive leaps, and mid-air, ninja-style kicks.

Timothy Higham, an associate professor in the Department of Evolution, Ecology and Organismal Biology at UCR, is a coauthor on two papers published today in Functional Ecology and the Biological Journal of the Linnean Society that present detailed analyses of the behaviors and biomechanics of both kangaroo rats and rattlesnakes.

"Both rattlesnakes and kangaroo rats are extreme athletes, with their maximum performance occurring during these interactions," Higham said. "This makes the system excellent for teasing apart the factors that might tip the scale in this arms race."

The research team documented the interactions between kangaroo rats and rattlesnakes in the wild by using radio telemetry to patiently track the hunting behavior of free-ranging rattlesnakes, and then placing high-speed cameras to record snakes hunting in locations frequented by kangaroo rats. The resultant videos provide the first ever detailed look at the maneuvers that kangaroo rats use to defend themselves against a deadly predator.


Video of kangaroo rat defensively kicking a rattlesnake while jumping

"These lightning-fast and powerful maneuvers, especially when executed in nature, tell us about the effective strategies for escaping high-performing predators," Higham said. "Those that are successful at evading the strike will suggest ways in which the kangaroo rat might be evolving in response to the intricacies of the predatory movements."

A blink of the human eye can last just 150 milliseconds. In contrast, the research team found that the rattlesnakes frequently launched from absolute stillness to reach the kangaroo rats in less than 100 milliseconds. The researchers were surprised to find that the kangaroo rats turned out to be even faster, with typical reaction times around 70 milliseconds.  Their data indicate that some kangaroo rats initiated jumps within just 38 milliseconds of a snake starting its strike. 

"Kangaroo rats that responded quickly were frequently able to jump clear of the snake completely, leaving the serpent biting nothing but dust as the kangaroo rat rocketed 7-8 body lengths into the air," said Rulon Clark, an associate professor of biology at San Diego State University and a coauthor on both research papers. "But in perhaps the most surprising finding of our research, kangaroo rats that did not react quickly enough to avoid the strike had another trick up their sleeves: they often were able to avoid being envenomated by reorienting themselves in mid-air and using their massive haunches and feet to kick the snakes away, ninja-style."  

One video shot by the students on the research team shows a kangaroo rat successfully kicking a snake.  The snake is sent flying through the air and crashing to the ground several feet away while the kangaroo rat bounds off.  Such defensive kicks solved a mystery that had puzzled the team for years: the group's previous research showed that kangaroo rats often emerged from seemingly successful snake bites unscathed, but it was not clear how. The researchers even tested the blood of kangaroo rats to be sure that they weren't physiologically resistant to snake venom, the way some squirrel and opossum species are. 

"Our previous work used lower-speed cameras, and although it seemed as though snakes had successfully struck their prey, the movements of the animals at the moment of impact was too blurry to see details," said Malachi Whitford, a doctoral student at San Diego State University and the lead author on one of the papers.  "In this new work, we used cameras with much higher recording speed and resolution, which helped show in exquisite detail that kangaroo rats not only have record-breaking reaction time, but can also use their long tails to reorient their bodies while jumping, thereby optimally positioning themselves for both defensive kicking and landing on their feet."

Catching prey and avoiding predators are central to the reproductive success of animals.  Kangaroo rats' highly sensitive hearing allows them to hear low-frequency sounds and detect sudden surprise attacks, necessary for avoiding predators. They also have enlarged hindlimb muscles and thick tendons, allowing for the rapid vertical leaps and high accelerations. 

Rattlesnakes are classic ambush predators. They hunt by hiding and remaining nearly motionless for prolonged periods. They strike at prey that gets too close. The prey avoids being struck by initiating a successful evasive maneuver. In the wild, both predator and prey can alter the outcome at multiple stages of an interaction in ways not readily apparent in the lab. 

"Our work, which, to our knowledge, is the first to describe the kinematics of evasive leaps by bipedal rodents avoiding actual attacks from predators, supports the idea that bipedalism may have been favored in kangaroo rats because it allows for the rapid and powerful leaps needed to avoid ambush predators such as vipers and owls," said Grace Freymiller of San Diego State University, the student lead author of the second paper.

https://phys.org/news/2019-03-high-speed...o-rat.html


Journal Reference:
Grace A Freymiller et al. Escape dynamics of free-ranging desert kangaroo rats (Rodentia: Heteromyidae) evading rattlesnake strikes, Biological Journal of the Linnean Society (2019). DOI: 10.1093/biolinnean/blz027

Abstract
Many animals exhibit morphological specializations driven by the extreme selective pressure of predation, and understanding how such specializations shape escape behaviours can elucidate the evolutionary context of these morphologies. We examined the kinematics of the evasive leaps of desert kangaroo rats (Dipodomys deserti) during strikes from sidewinder rattlesnakes (Crotalus cerastes) to understand the potential importance of predator evasion in shaping bipedalism in desert rodents. We found that kangaroo rats escaping from snake strikes relied on rapid response times to initiate effective evasions. During jumps, their enlarged hindlimbs propelled vertical leaps that were multiple body lengths into the air, and these leaps were often accompanied by mid-air kicks and other manoeuvres that deterred snakes. Although we found high levels of variability in kinematic factors, all kangaroo rats that successfully evaded attacks escaped in a path away from the snake and thus did not have random/protean escape trajectories. In general, our findings support the idea that bipedalism, which has evolved independently in several desert rodent lineages, might be favoured because it allows for rapid and powerful vertical leaps that are crucial for avoiding ambush predators, such as vipers and owls.

https://academic.oup.com/biolinnean/adva...m=fulltext
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