Most phyllostomid bats are colonial rather than solitary roosters, but roost size varies tremendously within and between species. Modal roost sizes within most species are relatively small and range from a few individuals to a few thousand individuals. A few species (the hot cave bats), in contrast, are highly colonial and roost in groups of tens of thousands to several hundred thousand individuals. Except for the flower-visiting, hot-cave bats, there does not appear to be a strong correlation between feeding habits and average roosting group size in this family. Vampires, fruit-eaters, many flower visitors, and certain carnivore/omnivores (e.g., Phyllostomus hastatus) sometimes live in roosts containing thousands of individuals. Small roost groups occur in pure carnivores, insectivorous phyllostomines, and a variety of flower-visiting and fruit-eating species (especially the tent-making stenodermatines).

Seasonal sexual segregation commonly occurs in many bats, including phyllostomids. Segregation usually involves the formation of maternity roosts by females. This behavior is most strongly developed in migratory glossophagines such as Lep-tonycteris curasoae, in which females sometimes form maternity roosts containing tens of thousands of adults. Single-sex maternity roosts also occur in non-migratory glossophagines and members of other subfamilies.

Like other Microchiroptera, phyllostomids use ultrasonic sounds for foraging and communication. Unlike other mi-crobats, however, most phyllostomids produce very low intensity sounds that contain only about one-thousandth the sound energy as similar-sized vespertilionid bats. Additional characteristics of their echolocation sounds include multiple harmonics, frequency modulation, and short duration. These sounds provide short-range (3.2-6.5 ft; 1-2 m) information about potential insect or other prey items in areas of high vegetation clutter. In addition to echolocation information, many phyllostomids use other sensory modes (e.g., vision such as the ground-feeding insectivore, Macrotus californicus, and many flower-visiting bats, or olfaction such as many fruit-eating bats) to find food. Certain phyllostomines, for example, locate prey using prey-generated sounds (e.g., singing katydids, Tonatia sylvicola, and singing male frogs, Trachops cirrhosus). Careful experiments have shown that plant-visiting phyllostomids use a combination of vision, olfaction, and echolocation to locate and gain access to their food.

Echolocation and other kinds of vocalizations are also used for communication in these bats. Babies communicate with their mothers using "double-note" calls (rapidly repeated se-

A Jamaican fruit bat (Artibeus jamaicensis) at a balsa flower. (Photo by Merlin D. Tuttle/Bat Conservation International/Photo Researchers, Inc. Reproduced by permission.)
A group of fringe-lipped bats (Trachops cirrhosus) huddles for warmth on Barro Colorado Island, Panama. (Photo by Merlin D. Tuttle/Bat Conservation International/Photo Researchers, Inc. Reproduced by per-

though most species are sedentary and do not migrate among habitats during the year, a few species are known to undergo seasonal migrations. Relatively short-distance (<62 mi; 100 km) altitudinal movements are known to occur in three Mexican or Central American species—two frugivores, Carollia perspicillata and Sturnira lilium, and the nectar bat, Leptonyc-teris curasoae. Longer distance latitudinal migrations occur in three arid-zone nectar bats: Leptonycteris curasoae, L. nivalis, and Choeronycteris mexicana. Movements of over 620 mi (1,000 km) occur in females of L. curasoae as they move between spring maternity roosts in the Sonoran Desert and their late fall mating sites in west central Mexico. The lonchophylline nectar bat (Platalina genovensium) is also thought to undergo substantial migrations in the Andes of Peru.

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