A research team including the University of Tokyo and other institutions succeeded for the first time in the world in filming a bat capturing a small bird in the air. They pointed searchlights into the night sky and tracked the bats using digital cameras. Bats possess the ability of "echolocation," using the echoes of sounds they emit to determine the distance, direction, and size of surrounding objects. This achievement provides a clue to understanding the advanced foraging strategies that make use of this ability.
Photographed by Noboru Numata of the Japanese Migratory Bird Conservation and Research Group
Bats have diverse diets, feeding on insects and plants, and some species prey on terrestrial vertebrates and birds. According to Associate Professor Dai Fukui, who specializes in ecology, at the Graduate School of Agricultural and Life Sciences at the University of Tokyo, fecal analyses have revealed that three bat species in temperate regions, including Japan, which normally feed on insects, prey on small birds during certain seasons.
In Japan, among these species, N. aviator, which has a wingspan of about 40 centimeters and weighs around 40 grams, feeds on birds. However, directly observing bats capturing birds has been difficult, and two competing hypotheses have been proposed: that they attack birds resting at their roosts, or that they capture birds in flight. In recent years, evidence from GPS (Global Positioning System) tracking and other studies has lent support to the view that they capture birds in the air.
Based on information that N. aviator had been observed at a bird-watching site in Aomori Prefecture, Fukui conducted observations with bird experts over eight nights from October 11 to 18, 2023. They illuminated the sky with searchlights and tracked N. aviator with digital cameras whenever the bats appeared. They filmed the bats chasing birds and capturing them in the air.
The researchers observed bats chasing birds on 56 occasions. In 22 of these cases, the bats made contact with birds while attempting to capture them. Actual captures were recorded in six cases. Of the 33 cases in which the bird species could be identified, most involved small birds weighing 30 grams or less, including 15 Japanese Bush Warblers, nine Black-faced Buntings, and four Grey Buntings. The bats also chased birds larger than themselves, such as Japanese Green Pigeons and Eyebrowed Thrushes, but were unable to get close enough to make contact.
These observations provide direct evidence that N. aviator captures birds in the air. Future studies will investigate where and how the bats consume captured birds and how they make use of their echolocation abilities. The research was conducted jointly with Doshisha University, the Okhotsk Bat Research Group, the Japanese Migratory Bird Conservation and Research Group, and other organizations. The paper was published on July 19 in the journal Ecology.
Original article was provided by the Science Portal and has been translated by Science Japan.