Bats can be found in virtually every habitat available from rainforests to deserts, montane forests to seasides. Bats have two basic habitat requirements: roosts, or places to spend the day or hibernate, and places to feed. The actual selection of roosting or foraging habitat depends on the species and the time of year.
Roosts of bats can be divided into four broad categories: hollows, crevices, foliage, and "other." Hollows, situations where the roosting bat hangs free by its hind feet, may be inside trees, rocks (caves, mines), buildings, or even birds' nests. An unexpected discovery was of round-eared bats (genus To-natia, family Phyllostomidae) roosting in hollows in the bases of arboreal termite nests. Crevices and cracks, situations where the bats' venter is against one surface (and its back may be close to the other), occur in rocks, trees (under bark or in wood), and buildings. Bats roosting in foliage may hang from branches of trees, or among or under leaves. The "other" category includes bats roosting in unfurled leaves or in tents.
In the New World, three species of disk-winged bats (genus Thyroptera) roost in unfurled leaves of plants like he-liconia or bananas. These roosts are available for about a day, because as the leaves grow they unfurl, obliging the bats to move regularly to new leaves. Suction disks on the wrists and ankles allow the bats to move about on the smooth leaf surfaces. In Africa, rufous mouse-eared bats (Myotis bocagei) and African banana bats (Pipistrellus nanus) roost in unfurled banana leaves. These bats lack suction disks.
In the Neotropics, India, and Southeast Asia, a number of species of bats roost in tents. Tents, usually leaves modified by biting, shelter bats from direct sunlight and rain. One or two species of short-nosed fruit bats (genus Cynopterus, family Pteropodidae), one species of plain-nosed bat (a yellow bat, genus Scotophilus), and about 18 species of New World leaf-nosed bats (family Phyllostomidae) use tent roosts. In the New World tropics, individual tents can last for several months and be occupied by a succession of bats. There is relatively little information about how bats build tents. In India, male lesser short-nosed fruit bats (Cynopterus brachyotis) build tents that are occupied by the tent-builder and groups of females and their dependent young.
Flattened skulls are examples of morphological specializations associated with roosting in narrow spaces or in roosts with small entrances. Good examples occur among free-tailed bats (genera Platymops, Sauromys, and Neoplatymops) that roost
under rocks. Bamboo bats (plain-nosed bats, genus Tylonyc-teris) roost inside the hollows of bamboo stems. They enter these roosts through small holes made by bruchid beetles. These bats have very flattened skulls. Bats roosting on rough surfaces (e.g., under stones) may have wart-like projections on the forearms (e.g., Platymops, Neoplatymops). Species roosting on very smooth surfaces can have suction disks that are best developed in disk-winged bats, either from the New World (family Thyropteridae) or in Madagascar (family My-zopodidae).
Roosting bats readily exploit artificial structures as roosts. People may find bats roosting in their homes. Around buildings, bats can be found roosting in attics or eaves, behind shutters, even among the folds of rolled up patio umbrellas. Bats also roost in the expansion cracks of bridges, a famous example being the Congress Avenue Bridge in downtown Austin, Texas, United States. Bats frequently roost in abandoned mines and in active underground water conduit systems. Today, it is common for people to erect bat houses or bat boxes to provide additional roosting opportunities. Some bat houses have resident bats, while others do not. It remains to be determined if bat populations are limited in size by the availability of roosts.
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