Desert Shrew
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| Notiosorex crawfordi (Coues, 1877) |
The Desert Shrew, Notiosorex crawfordi, is a small shrew that can be found in the southwestern United States and northern Mexico. It is a member of the Order Eulypotyphla and the Family Soricidae . It is was the only known member of the genus Notiosorex until 2 species N. villai distributed in Tamaulipas, Mexico, and N. evotis distributed along the northwest coast of Mexico were named [1]
The desert shrew is one of the smallest desert mammals and one of the world's smallest homoiotherms. When fully grown it will only grow to a size of about one and a half to two inches long, half of which is the tail and it will only grow to a weight of about 3 to 5 grams. It is a gray-brown with light gray under parts. The long tail is gray with it being lighter underneath. It has small, but relatively prominent ears.
A desert shrew is born during the summer months to a litter size of three to six. When born the desert shrew is naked, pink and is about the same size as a honeybee. They grow rapidly and reach their adult size in about four to five weeks. As babies their diet is consisted of milk that the mother produces, without the aid of water. After two to three weeks, the diet is changed into food that is brought back to the nest and then regurgitated into their mouths. By the time fall rolls around, the desert shrew is out of the nest and are on their own. As an adult, the diet changes from the regurgitation of food to real food that they kill themselves. Desert shrews will eat lizards, small mice, and scorpions. The main food source for the desert shrew, though, is a wide variety of arthropods. Since desert shrews have a very high rate of metabolism, they will eat up to 75 percent of their body weight every day. Although, it is known that some will eat their own weight in food. This can be dangerous since it can overheat the animal. The amount of heat produced by the high rate of metabolism and the heat gained from its surrounding environment will give a high risk of overheating.
The desert shrew, unlike most shrews, does not have access to an abundant water supply. To conserve the little water that shrews do absorb is to find shelter that will protect them from the harsh external temperatures. Desert Shrews do not construct their own burrows or use the ones made by other animals. Instead they build small nests that can be found in packrat houses or under dead agaves.
Another way the desert shrew will conserve its precious water is by doing most of its activities at night. This is odd behavior among shrews, since most will hunt day and night since it does not take long for a shrew to starve to death. The desert shrew has poor vision, so it uses its highly-sensitive ears and long nose to hunt down its prey. It will also use a tactic similar to that of a bat and use echolocation with high-pitched squeaks to hunt down prey. It will then compile a large amount of food during the night so it will not have to go out into the day. To keep from losing any water from its victims the desert shrew will bite off the legs and then crush the victim's head so as not to kill it but to keep it fresh and unable to move.
Since water loss is a huge problem for the desert shrew, it has adapted to this by reducing two major ways of water loss. One of these ways is through respiratory. While breathing the desert shrew will inhale air that will be warmed to body temperature and will absorb water vapor from the nasal walls. Exhaled air is cooled and so as the air is exiting the water vapor from the air clings to the nasal passage. This keeps in more water vapor than if the air was exhaled at body temperature. Water loss is reduced even more through respiratory because the desert shrew takes fewer breaths than other shrews and they have the lowest resting metabolic rate of all shrew species. The other form of reducing water loss is through the form of urine.
Desert Shrews have to expel a large amount of nitrogenous waste from their body. This is potential for a large loss of water when urinating. Fortunately, the desert shrew is able to reduce the amount of water loss during this action as well. They do this by concentrating a large amount of urea in their urine. When urea is being concentrated it uses basically the same principle as conserving water while breathing. The end result of all this concentration is urine that is four times more concentrated than that of a human. Since it takes only a few drops of urine to expel all the waste from a desert shrew in one day, this saves a huge amount of water.
Even with all of these adaptations to help the desert shrew to survive in the harsh environment of the desert, it still only lives for a relatively short time. Since it hunts at night, the desert shrew is susceptible to nocturnal hunters such as snakes and owls. Although it can emit a musky odor that makes it seem less appetizing to mammalian predators it still lives for only about a year or so in the wild.
[edit] Species
- Gray or Desert Shrew (N. crawfordi)
- Cockrum's Gray Shrew (N. cockrumi)
- Long-eared Gray Shrew (N. evotis)
- Villa's Gray Shrew (N. villai)
[edit] References
1 Carraway, L. N., and R. M. Timm. 2000. Revision of the extant taxa of the genus Notiosorex (Mammalia: Insectivora: Soricidae. Proceedings of the Biological Scoiety of Washington, 113:302-318.
- Insectivore Specialist Group (1996). Notiosorex crawfordi. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006. Database entry includes a brief justification of why this species is of least concern
