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Free-Tailed Bats and Mastiff Bats: Molossidae

Behavior And Reproduction

Molossids are generally strong flyers that can fly quickly for long periods of time. Like all bats, these bats are nocturnal, meaning they are active at night. These bats fly all night, whereas other bats typically fly a short time during the night. They can fly six or seven hours without stopping.

Molossids catch their prey using echolocation (eck-oh-loh-KAY-shun), a technique where the bat detects objects by receiving the reflection of sounds it produces. They fly with their mouths open and send out echolocation calls. They forage, search for food, in groups and head towards large swarms of insects. They also look for food around streetlights, which attract insects, such as moths. They generally catch their prey while they are flying.

Because they live in warm areas, molossids do not need to hibernate (become inactive in the cooler months to conserve energy). Some of these bats travel to even warmer areas in the winter.

Molossids have a range of roosting habits, from solitary to social, living in large colonies (groups) of millions of individuals. Between those two extremes, sizes of colonies range from hundreds to thousands of individuals. Most of these bats do form colonies in the size of a few tens to several hundred individuals. Molossids generally return to their roosting sites every year. Their colonies generally give off a strong, musky odor.


A colony with thousands or millions of bats will produce a lot of guano, and people have been putting these droppings to use for a long time. Before people began to sell guano as fertilizer, the Confederate Army was using guano during the Civil War (1861–1865), as a source of gunpowder. It is thought that this guano was collected from the Brazilian free-tailed bat. In the late 1800s came the discovery of the millions of bats in Carlsbad Caverns, New Mexico, and their associated guano, which was valuable. In the early 1900s mining operations started in the caves, using mining cars to transport guano to the cave entrance. Most of the guano was shipped to southern California to help the developing citrus industry. In about twenty years of operation, over 100,000 tons of guano was taken from Carlsbad Cavern. Six companies attempted to make a profit in this venture, but all failed due largely to high transportation costs. Bat droppings in Carlsbad Caverns over the past 17,000 years have formed guano deposits covering several thousand square feet to a depth of almost 50 feet (15 meters)!

Little is known about the mating habits of most molossids. Most species are considered polygynous (puh-LIJ-uh-nus), meaning the male mates with more than one female during the mating season. Females of most species appear to produce one offspring per year. Two young are born on rare occasions, and the black mastiff bat in Trinidad possibly has two litters per year. During pregnancy, females generally form maternity colonies that are separate from the males. In these colonies, females relocate and nurse their young independently.

Additional topics

Animal Life ResourceMammalsFree-Tailed Bats and Mastiff Bats: Molossidae - Physical Characteristics, Geographic Range, Habitat, Behavior And Reproduction, Molossids And People, Conservation Status - DIET