Bats that Eat Passerines on the Wing
Every spring, billions of passerines (Passeriformes) migrate through the night sky over southern Spain at high altitudes. During this seasonal movement, the greater noctule bat (Nyctalus lasiopterus) is able to chase migrating birds in the dark, capture them in mid-air, and consume them while still in flight.
This observation was made by fitting 14 greater noctule bats with high-resolution multisensor biologging tags that recorded their flight altitude, acceleration, acoustic activity, and fine-scale foraging behavior. The study also analyzed bird DNA in bat feces and examined passerine wings found beneath the bats’ hunting grounds. Earlier work had already detected passerine remains in the feces of greater noctule bats, suggesting that they prey on birds. The unanswered questions were more difficult: where do these bats locate birds, how do they overtake them, and how can they handle prey that may approach half of their own body mass and still struggle vigorously?
The tags recorded 611 attack events in total. Of these, 609 resembled ordinary insect attacks: they were brief, involved only a few echolocation buzzes, and occurred at relatively low altitudes. Here, a buzz refers to a rapid sequence of high-repetition ultrasonic echolocation calls produced during a prey capture attempt. In 95% of these attacks, the bats produced fewer than five buzzes, the attack lasted less than 10 seconds, the average altitude was about 53 meters, and the median duration of mastication sounds was about 11 seconds. These patterns are consistent with bats hunting flying insects. Two attacks, however, were very different. In both cases, the bats had first climbed to high altitude, then pursued their prey in a fast downward sprint. The chases lasted 30 to 176 seconds, wingbeat frequency increased from 7.2 to 8.5 beats per second, and body acceleration rose sharply. These were not brief capture attempts; they were demanding aerial pursuits.
In one successful attack, a greater noctule bat climbed to about 1,200 meters, detected a target at altitude, and began chasing it downward before capturing it near the ground. Immediately after capture, the tag recorded 21 distress calls from the prey. By comparing these calls with recordings from 19 passerine species previously identified in the feces of greater noctule bats, the prey was identified as a European robin (Erithacus rubecula). This was followed by 23 minutes of mastication sounds while the bat continued flying. It did not land and did not switch to attacking other prey. This indicates that the bat completed its feeding in the air.
Most passerines lack high-frequency hearing and therefore cannot detect the ultrasonic signals that greater noctule bats use to track prey. For the bat, this provides a sensory advantage that allows a stealthy approach. During bird chases, the buzz structure used by greater noctule bats was highly similar to that used during insect attacks. Echo data also showed that targeted birds made vertical escape movements, similar to the evasive responses birds use against falcons during daytime migration. In the night sky, however, they may have little warning before a bat closes in. They may only detect the bat at close range by hearing its wingbeats, or recognize the attack once physical contact occurs. When the bat reaches the bird, it may first seize or hook the prey with its hind feet, using the uropatagium to support, scoop, or restrict the bird’s movement, before delivering a lethal bite with the mouth. In the recording, an echolocation pause of about one second occurred just before the final distress call, consistent with the bat using its mouth to bite the prey at that moment.
Passerine wings found beneath the bats’ hunting grounds provided another clue. The study examined 11 wings with x-ray scans and performed predator DNA barcoding on three of them. These analyses found bite marks and greater noctule bat DNA on the wings. One wing belonged to a melodious warbler (Hippolais polyglotta); the paper does not provide species-level information for the remaining wings. These results support a plausible prey-handling strategy: while in flight, greater noctule bats bite off the wings of the captured bird, immobilizing it and reducing drag so that they can continue carrying and eating it in mid-air. This resembles the way some aerial-hawking bats remove the wings of large insects before feeding, suggesting that a behavior originally used for handling large insects may have been co-opted for much larger avian prey.
Greater noctule bats, then, are not simply insect-eating bats in the usual sense. By combining darkness, altitude, speed, and ultrasonic echolocation, they can turn nocturnally migrating passerines into an accessible food resource.
Author: Shui-Ye You
Reference:
Stidsholt L et al. (2025). Greater noctule bats prey on and consume passerines in flight. Science.
Comments