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Kangaroo rat

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Kangaroo rat
Dipodomys nitratoides nitratoides.jpg
Scientific Classification
Species
  • D. agilis
  • D. californicus
  • D. compactus
  • D. deserti
  • D. elator
  • D. gravipes
  • D. heermanni
  • D. ingens
  • D. insularis
  • D. margaritae
  • D. merriami
  • D. microps
  • D. nelsoni
  • D. nitratoides
  • D. ordii
  • D. panamintinus
  • D. phillipsii
  • D. simulans
  • D. spectabilis
  • D. stephensi
  • D. venustus
Ord's Kangaroo Rat (Dipodomys ordii)
OrdsKangarooRat.jpg

Kangaroo rats (genus Dipodomys) are unique wonders of creation. As their name suggests, they have powerful hind legs that allow them to jump like a kangaroo. However, these desert creatures possess an even more amazing ability-- they are able to live their entire lives without drinking any water. Kangaroo rats can survive on a diet of dry seeds and obtain all the moisture they need from their metabolic water [1]. They are able to do this because of their well-adapted body systems, which are highly efficient in conserving water.

Contents

Anatomy

This skeleton of a banner-tailed kangaroo rat (Dipodomys spectabilis) shows the large hind legs for jumping and short front legs for digging.

Kangaroo rats are small rodents with large heads and eyes and long tufted tails. A kangaroo rat’s body can be two to six inches long, with a tail that can reach up to one and a half times the length of the body [2]. They usually weigh about 50 grams (2 ounces), although some species can be considerably larger (Mares 27).Their coloring ranges from a light, sandy tan to very dark brown, with a white underside. There are also various dark markings on the head and tail. These markings, as well as the number of toes on the hind feet (four or five), are used to distinguish between species [3].

Kangaroo rats can walk on all four legs but more often are seen jumping on their back two legs. This bipedal locomotion is more efficient, allowing the kangaroo rat to move faster and save energy. Their well-muscled hind legs can jump six to ten feet at a time [4][5]. The front legs, though not often used to walk, have strong claws that help the kangaroo rats dig their burrows [6]. The kangaroo rat’s tail gives it balance while running and jumping and acts as a rudder that allows it to change direction even while in the air [7] [8]. Kangaroo rats sometimes communicate by drumming on the ground above or inside their burrows with their hind feet(Reid 261). Most observers believe this sound is used as a warning against predators or a challenge [9]. Kangaroo rats have also been heard to utter squeals, chuckles, or growls, often when provoked, but for the most part they remain silent [10][11].

Kangaroo rats are nocturnal with large eyes that let them see in the dark and small external ears with a large chamber in the middle ear that picks up sounds such as those predators make [12]. When kangaroo rats move around at night they use their whiskers to find their way around. They jump very close to the ground and have 42 facial muscles that receive information about the terrain from the whiskers as they drag on the ground [13].

Kangaroo rats are desert animals and have many unique and amazing adaptations in order to survive in their arid environment. These adaptations allow the kangaroo rat to live its entire life without drinking any water. They get all they need from their metabolic water, which is produced when their bodies break down food [14]. Kangaroo rats do not have sweat glands and do not pant, preventing them from losing water due to evaporation [15]. They also have a gland on their backs that excretes an oil to coat the fur, once again aiding in retaining water [16][17]. Kangaroo rats regularly take dust baths to prevent an excess of oil from building up, which can cause sores and matted fur [18]. Kangaroo rats avoid losing water in respiration with long nasal passages that cool exhaled air, causing moisture to condense in the nose. The moisture can then be absorbed by the body [19]. Kangaroo rats spend the hot days inside their extensive underground burrows. The humidity is much higher inside the burrows, preventing the kangaroo rats from losing as much moisture through respiration as they would in the dry desert air [20].

Kangaroo rats have highly efficient kidneys that produce much more concentrated urine than most other mammals. Kidneys filter waste materials, water, and chemicals out of the blood. Water and some of the chemicals such as sodium or potassium are needed to live and are reabsorbed by the blood in the kidney's many nephrons [21]. Most water is returned to the blood in the part of the nephron called the Loop of Henle, which has been found to be much longer in kangaroo rats than in other mammals or man [22]. More water can be absorbed in the extra long Loop of Henle, resulting in highly concentrated urine and preventing kangaroo rats from losing more than a few drops of water a day as nitrogenous waste [23].

Reproduction

Kangaroo rats reproduce through sexual reproduction. They have a long breeding season that extends from February to October [24]. During this long season, some of the females may have two or even three litters, one early in the season and others later on [25]. The gestation period is roughly thirty days. Litters usually consist of one to three pups, although they may have up to six [26]. Pups are born hairless and with their eyes closed. They have their adult color pattern at birth [27]. The pups live in the mother's burrow until they are ready to leave after six weeks (Maser 168).

The kangaroo rats often reproduce in response to favorable environmental conditions. The availability of water and green vegetation are crucial to the survival of the pups. While some kangaroo rats are able to reproduce all year long because of a better, more constant climate, this is not possible for all species (Maser 168). When food and water are plentiful, the females are stronger and their bodies are able to produce litters. After droughts, however, females will rarely reproduce [28]. This is an adaptation by kangaroo rats that ensures the most success in giving birth because the females will be stronger and will be able to regain any water they lose, and provides the greatest opportunity for the pups to survive [29].

Ecology

Kangaroo rat trail leading to the burrow entrance
The opening of a kangaroo rat's burrow

Kangaroo rats live in dry, hot, desert habitats. They can be found in Canada, the United States, and Mexico. They make their homes in dry, sandy or rocky soil with little to no vegetation [30]. The dry soil allows the kangaroo rats to easily dig their burrows, which are often extensive, even though they usually hold only a single kangaroo rat unless it has pups or a mate [31]. The burrows go into the ground at an angle and have many connecting passageways and chambers for living and storing food [32]. Mounds often develop around the burrow entrances, which can be clearly seen from far away because the kangaroo rats harvest the grasses within a 15 foot radius around their burrows [33]. Trails leading away from the burrow entrances are also usually present. These are formed as the kangaroo rats follow the same paths over and over again on the way to collect food or visit other burrows [34] [35]. Kangaroo rats are independent animals, but they can often be found living in large colonies. In these cases, they maintain separate burrows, which are spaced according to food availability [36]. Kangaroo rats have been known to plug the entrances to their burrows during the day. This behavior traps extra moisture and maintains a more constant and comfortable temperature inside the burrow [37].

Kangaroo rats mainly eat seeds produced by the grasses in their desert environments, although they occasionally consume green vegetation, insects, and some fruits as well [38]. Kangaroo rats gather food at night. They hop on their two back legs when gathering food, feeling their way through the dark with their whiskers. They have a very strong sense of smell as well, and can pick up the odors of seeds buried up to eight inches under the soil (Mares 29). Once they have located seeds under the soil, kangaroo rats rapidly sift the seeds from the loose sand using their forepaws and place them in their external, fur-lined cheek pouches (Mares 28). They stuff as much as they can into the cheek pouches and bring what they collect back to their burrows to be stored for later. Kangaroo rats can turn these pouches inside-out to empty them and pull them back in again [39].

Kangaroo rats have several methods of storing food. Some, such as the Merriam's Kangaroo Rat (D. merriami), store seeds in small caches around their burrow mound and dig the seeds up later [40]. Other kangaroo rats store food inside their burrows in special chambers. Food stored in the burrow gains more moisture from the humid air, providing more water for the kangaroo rat [41]. However, when seeds are stored inside the burrow they will mold if they become too moist, so the kangaroo rats must continually move the seeds to drier areas of the burrow (Mares 28). The Giant Kangaroo Rat stores its food around the burrow entrance and brings the seeds inside when they have been ripened and dried by the sun [42]. Often the stored food is used to bring the kangaroo rat through winter, droughts, and other periods when food is unavailable. The kangaroo rats need large stores of seeds to survive such conditions because they do not hibernate during the winter and must keep eating [43].

Predators of kangaroo rats include owls, coyotes, foxes, badgers, bobcats, and snakes [44]. Kangaroo rats are often able to escape from these predators by detecting them early. Kangaroo rats have large eyes on near the top of their heads to see predators coming from above, even in the dark (Mares 30). They also have acute hearing and quick reflexes. At a slight sound or movement they bound away on their powerful hind legs, zigzagging from side to side as they run from predators (Mares 30). Kangaroo rats are also often killed by cars while they are out at night to gather food [45].

Giant Kangaroo Rats Monitored From Space

The Giant Kangaroo Rat has been on the endangered species list for years. The population has been declining because their habitat is being used as farmland. A total of 90% of the Giant Kangaroo Rat's original habitat is now used for agriculture [46]. Giant Kangaroo Rats living in the Carrizo Plain in California are a keystone species, meaning that they provide food and habitat conditions necessary for other animals [47]. They provide food for predators such as the kit fox and cut grasses to a length preferred by other endangered species. Their burrows provide shelter for antelope squirrels, blunt-nosed lizards, and other small animals [48] [49]. In addition, the behavior of cutting native grasses and piling them in a circle around the burrow opening creates a compost pile that returns nutrients back into the soil, promoting plant growth in those areas [50].

Since Giant Kangaroo Rats are so essential to their environment, scientists have been monitoring them to determine a course of action for the future in the Carrizo Plain. In the past, the population has been counted by trapping or using hand-drawn maps from aerial surveys, but both methods are slow, unreliable, and not easily replicated from year to year. Recently, a research project was launched by doctoral student Tim Bean and biologist Scott Butterfield that will use satellite images from an Israeli defense satellite to monitor kangaroo rat populations [51]. This is possible because, as Giant Kangaroo Rats collect food, they clear the grasses around their burrow mounds in large circles that appear as dots on the satellite photos [52]. By counting the dots, researchers are able to estimate the population fairly accurately because burrows almost always hold only a single kangaroo rat.

The Giant Kangaroo Rat population fluctuates according to the amount of rainfall each year [53]. The amount and type of vegetation also plays a key role in population size. When there are more grasses, the kangaroo rats may still be unable to find enough food if the grasses are the tall, foreign varieties rather than the short, native plants. When food is scarce, kangaroo rats will not reproduce as often, resulting in a smaller number of offspring as well as the possibility of adult rats dying from lack of food [54]. Options considered to reduce the amount of nonnative grasses include introducing cattle to graze in specific areas and using controlled burns [55]. In the future, scientists hope to be able to better determine which responses to environmental changes will be most effective in preserving the Giant Kangaroo Rat species.

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