Mojave National Preserve - Mammals

Over 4,600 species of mammals have been described worldwide, 416 of which can be found in the United States. Of these, fifty-one species representing sixteen families have been documented within the Preserve. Only mammals possess hair (or "fur"), which is secondarily lost in the adults of species. Hair has several functions, including insulation, protection, sensory, camouflage, and communication. Female mammals produce milk from mammary glands (modified sweat glands) with which they nurse their young. Mammals are the only animals that have three bones in the inner ear (the malleus, the incus, and the stapes). This three-boned structure serves to amplify sounds, a trait which would have been highly advantageous to early mammals, which were probably mainly nocturnal and would have had to rely heavily on the sense of hearing (and smell). Many modern mammals are still nocturnal (active at night), although many others are diurnal (active during the daytime) or crepuscular (active around dusk and dawn).

Living mammals are generally endothermic, homeothermic, and tachymetabolic, a suite of terms which was once inaccurately named "warm-blooded". Endothermic organisms such as mammals regulate their body temperatures internally by utilizing processes such as altering bloodflow and muscle contractions. Organisms which maintain a constant (or nearly constant) body temperature which is usually significantly above the ambient temperature are referred to as homeotherms . Finally, the resting metabolism of an organism can be described as either high or low. Resting metabolism is the amount of internal activity (such as cellular respiration) in an animal when that animal is at rest. Organisms that have high resting metabolisms are termed tachymetabolic. (For a description of the converse of these conditions refer to the section on reptiles.) Of course there are exceptions to the rule, and true hibernators have a very low resting metabolism (bradymetabolic) and low body temperature during hibernation. The endothermic, homeothermic, and tachymetabolic nature of mammals allow them as a group to inhabit every major land mass and body of water on the planet.

Black-tailed jackrabbits ( Lepus californicus ) are among the most commonly seen of desert mammals. Jackrabbits are larger and leaner than resident cottontail rabbits ( Sylvilagus sp.) with longer legs and ears. A significant amount of blood flows through the many blood vessels of a jackrabbit"s ears, which helps dissipate heat, an important adaptation in the desert. Jackrabbits are mainly nocturnal and may be seen in large numbers by the side of the road at dusk. However, they are easily startled and will frequently bolt out from under bushes where they spend the daylight hours resting. Female jackrabbits are larger than male, a condition which is not common in mammals.

The coyote ( Canis latrans ) is another frequently seen desert mammal. One of four members of the dog family (Canidae) found within the Preserve, they are found throughout much of North and Central America, often in areas once populated by wolves. However, the coyotes of the desert are significantly smaller and are lighter in color than coyotes living in other habitats. The success of coyotes may be attributed to their adaptability; for example, mainly carniverous, they may eat plants and will also consume significant amounts of carrion. Although largely nocturnal, the coyote may also be seen during the day. Coyotes, the most vocal of the Mojave mammals, have a complex vocabulary which includes the distinctive and unforgettable howl call.

Unique among mammals are bats (Order Chiroptera), the only mammals with true wings capable of powered flight. Flight evolved three times in vertebrates, in the extinct pterosaurians, in avians (birds), and in chiropterans (bats). This is a clear example of convergent evolution, when animals with different ancestors evolve similar adaptations (such as flight). Scientists theorize that bats evolved from gliding ancestors, whereas birds likely evolved from bipedal ancestors that ran quickly along the ground. Bats and birds both have lightweight skeletons and a keeled sternum for the attachment of flight muscle but differ in several important ways in how they achieve flight. Whereas the bird wing is primarily supported by the forearm and modified wrist bones, bat wings are supported by the arm and four greatly elongated fingers of the hand. In addition, birds have feathers on their wings, while bats have only a thin membrane. Bats also have a membrane stretched between the legs (the uropatagium) which helps stabilize flight and also capture prey. All of the ten bat species found within the Preserve are microchiropteran bats, which utilize echolocation to capture primarily insect prey. Echolocation is a sensory system in which animals emit high-frequently sound and use the reflected echoes to determine the location of objects. Bats are not the only animals to utilize echolocation (think dolphins), another striking example of convergent evolution.