Keywords Mammals

Hind limbs of bats are also greatly modified, being "backward" compared to those of other mammals; thus, the knees point backward and the foot sole forward. This makes it easy for a forward-flying bat to land on a projection and then move to hang upside-down in the bat's normal resting position.

The flight membranes extend outward from the body and from the hind limbs to the arm and fifth digit, between the fingers and from the hind limbs to the tail in most species. A few bat species are tailless and, in some, the tail is free of the tail membrane (uropatagium).

Taxonomy
Two very different suborders of bats exist. The suborder Megachiroptera contains only one family of Old World fruit bats. The species in this suborder feed exclusively on either fruit or on nectar and pollen. Flying foxes, the world's largest bats, with wingspans of up to 1.2 metres, belong to this group. The suborder Microchiroptera includes 17 other families.

Megachiropterans may be distinguished by the presence of a claw on each thumb and a claw on the adjacent digit. Microchiropterans only bear a claw on each thumb.

Navigation
Megachiropterans appear to depend far more on their senses of sight and smell and do not seem to use echolocation. Nearly all microchiropterans navigate in darkness using reflected sound as a guidance mechanism. The shape of the bat's mouth, including the wide space between the first 2 upper incisor teeth, produces almost a trumpet or megaphone-shape which allows sound to be directed with minimum obstruction. Well-developed hyoid bones extend from the larynx, or voice box, to the auditory bullae, where sound is received. This system permits bone-to-bone conduction of sound to the ear as the sound is produced. The remainder of the sound is projected from the mouth. Any sound reflected from an object and received by the external ear arrives later than the signal conducted via the hyoid bones.

In some way bats are able to determine both distance and direction of the object reflecting sound. The bat's external ear, or pinna, is large, although there is considerable variation between species. A thin, fleshy projection, the tragus (resembling a secondary ear), arises from the inner base of each ear.

Diet
Microchiropterans eat many more varieties of food than do megachiropterans. Most microchiropteran species eat INSECTS but some feed on SCORPIONS and SPIDERS; others feed on FISH, small REPTILES, rodents, birds and even other bats. A few of these species feed on pollen or fruit. Three species of vampire bats that range from northern Mexico to northern Argentina are the only mammals that feed solely on blood.

HibernationBats active in temperate areas during the warm season either hibernate or migrate to avoid food shortage during the winter. Hibernation is typically in caves with temperatures only a few degrees above freezing. During daylight, bats shelter in crevices in rock, under loose bark or in tree leaves. Others prefer caves, mines or buildings. Some caves, such as the Carlsbad Caverns in New Mexico, have sheltered more than 2 million bats at a time.

PopulationBats have remarkably low reproductive rates. Females bear only 1 young per year in most species and the largest litters reported have only 4 young per year. Bat populations in many parts of North America have been declining dramatically. Insecticide poisoning of both bats and their prey and the destruction of some bat colonies in rabies control projects may be major contributing factors.

Author DONALD PATTIE

Links to Other Sites
Canadian Biodiversity Website
A great information source for all budding biologists. Learn about biodiversity theory, natural history, and conservation issues. From McGill’s Redpath Museum.