There are three species of bats that eat birds. We know this because we found feathers and other bird remains in their feces. What we didn't know was how exactly they hunt birds, which are slightly heavier, faster and stronger than the insects that bats typically feed on.
To find out, Elena Tena, a biologist at the Doñana Biological Station in Seville, Spain, and her colleagues attached ultra-light sensors to Nycthal Jaciopterlargest bats in Europe. What they found was stunningly brutal.
Stealth interceptors
Nycthal Jaciopteralso known as great evening bats, have a wingspan of about 45 centimeters. They have reddish-brown or chestnut fur with a slightly lighter underside and typically weigh between 40 and 60 grams. Despite this minimal weight, they are the largest of the three species of bats known to feed on birds, so a key challenge in gaining insight into how they hunt was finding sensors light enough to not impede the bats' flight.
Cameras that are just a conventional sensor were out of the question. “Bats hunt at night, so you need night vision cameras, which along with batteries are too heavy for a bat to carry. Our sensors had to weigh less than 10 percent of the bat's weight – four to six grams,” Tena explained.
Over the past decade, Tena and her team have explored several alternative approaches, including observing bats from the ground or using military-grade radar. But even then, catching bats red-handed remained impossible.
In recent years, technology and miniaturization have finally met Tena's needs, and the team found the right sensors for the job and, within two years, attached them to 14 large evening bats. The tags used in the study weighed about four grams, could last for several hours, and recorded sound, pitch and acceleration. This gave Tena and her colleagues a detailed picture of bat behavior in the night sky. The recordings included both ambient environmental sounds and the ultra-frequency pulses that bats use for echolocation. Combining altitude with accelerometer readings allowed the scientists to track the bats' movements during all their fast turns, dives and maneuvers.
