Ecology of Insect-eating Bats

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Bats are the only flying mammals that are active mostly at night and occur on all continents except Antarctica. Bats are ecologically diverse, with a range of species that specialize in feeding on fruit, nectar, blood, fish, small mammals, and insects. However, of the more than 1,100 known species of bats on Earth, the majority specialize in feeding on insects. In the United States for example, of the 45 different species of bats, 42 are insectivorous. These small creatures of the night are diverse in shape and size, with most relying on echolocation to detect insect prey and find their way through darkness. Many of these bats form colonies that feed on seasonally available insects from spring to autumn.

Examples of Insect fragments belonging to ground beetles, water boatmen, click beetles, weevils, scarabs, and adult antlions.
Examples of Insect fragments belonging to ground beetles, water boatmen, click beetles, weevils, scarabs, and adult antlions identified from various dissected guano pellets of different bat studies. Photo by: Ernest Valdez, USGS. Public domain.
Allen's big-eared bat (Idionycteris phyllotis), an insectivore known from the southwestern United States
Allen's big-eared bat (Idionycteris phyllotis), an insectivore known from the southwestern United States. Photo by: Ernest Valdez, USGS. Public domain.

Most insectivorous bats use seasonal feeding strategy to help build fat reserves during the summer and autumn, prior to their hibernation during winter - a time, generally, when insects are not available throughout most of the United States. Some of these bat species do not hibernate but instead migrate seasonally. It is believed that the timing of migration and routes that they take, such as those for the hoary bat (Lasiurus cinereus), might coincide with availability of their preferred insect prey.

Recently, many insectivorous bat species have suffered drastic declines in numbers due to new environmental stressors, both natural and human caused. One of these stressors is the emerging wildlife disease known as white-nose syndrome (WNS). This disease is caused by the fungus Pseudogymnoascus destructans and has been devastating colonies of hibernating bats in the eastern United States for several years. At present, there is no known cure for WNS, which continues to spread north-, south-, and westward. It is likely that the effects of declining insectivorous bat populations will influence insect populations, including possible increases, in some geographic areas of insects that are economic pests.

Brazilian free-tailed bat (Tadarida brasiliensis), a migratory insectivore known to consume insect pests of agriculture.
Brazilian free-tailed bat (Tadarida brasiliensis), a migratory insectivore known to consume insect pests of agriculture. Photo by: Ernest Valdez, USGS. Public domain.

 

Like WNS, the development of alternative energy in the form of industrial wind energy facilities is also having a harmful effect on bats through collisions with moving turbine blades. These fatal encounters often coincide with the autumn migration of bats. Why certain bats are susceptible to turbines remains unknown, yet feeding on insects may play a role in bat susceptibility. For example, the hoary bat is killed more often than any other species of bat at wind turbines in North America, and it is believed that certain prey types (e.g., noctuid moths) consumed by these bats may be locally and seasonally abundant around wind energy facilities.

Despite the high species and ecological diversity of insectivorous bats in the United States, little information exists on their diet. At FORT, biologists are investigating dietary habits of insectivorous bats, which will help provide insight into questions related to climate change, energy development, wildlife diseases, and conservation.

In the distance is Aguiguan (aka Goat Island), Commonwealth of the Northern Mariana Islands; home of the sheath-tailed bat.
In the distance is Aguiguan (aka Goat Island), Commonwealth of the Northern Mariana Islands; only known location for the endangered Pacific sheath-tailed bat (Emballonura semicaudata rotensis) seen above in carousel. Photo by: Ernest Valdez, USGS. Public domain.

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