Bats emit ultrasonic interference back and forth, and are happy to fight for their prey until one side finally gives up.
Before catching insects, bats emit a series of fast ultrasound signals to locate the exact location of prey through echoes. Scientists call these sounds “foraging sounds”, which also attract other bats that may be still foraging. When another bat arrives, it can block the sound waves emitted by the original bat. A new study shows that it is much like someone blocking the radio signal. This led to the original bat losing its delicacy, giving competitors a chance to grab food from the plate.
“It’s an exciting discovery,” said Milyam Cohenschder, a behavioral ecologist and bat pronunciation researcher at the University of Ulm in Germany, although he was not involved in the study. “Sonar jamming has always been an exciting possible explanation… Because some bats belong to the high-pitched species, this elegant design study is a very convincing argument.
Aaron Cochran, a biologist at Vick Forest University in Windsor City, North Carolina, first detected this interference signal when recording bat-moth interactions in Arizona. Other researchers have previously found that Mexican free-tailed bats (Santa Teresa Dog Kissing Bat) can emit at least 15 social signals and even regulate their own ultrasound pronunciation to avoid interference with other bats’ultrasound. To find out how bats use these signals, scientists placed a batch of ultrasound microphones in fields in Arizona and Mexico, and recorded bats’opposition rounds. They match the signal with the bat’s flight path so that they can see when the predator sends out the foraging signal and when the competitor sends out the interference signal. From the 3-D reconstructed images, Cochran and William Connor, a biologist at Vick Forest University, realized that bats are more competitive than cooperative, and they are always in control of efficient and destructive interference signals. “In fact, they use this signal at the critical moment of their prey,” Connor said.
Interference signals play a role through strong foraging signals eventually emitted by overlapping competitors. The sound waves generated by interference signals are enough to confuse bats’auditory neurons’ processing process and the ability to locate prey by using the number of clicks of ultrasound, i.e. echolocation ability. Of course, disturbed bats can reverse the situation by competing for their prey in the same way. “They send out ultrasonic interference back and forth, and they fight tirelessly for their prey until one side finally gives up,” Connor said.
In Arizona, scientists documented 145 bat battles for insects; 85.9% of predators failed when another bat sent out interference signals. If there is no interference from competitors, the success rate of predation will rise to 30%. Researchers also designed controllable, repeatable experiments to detect bats. They tied a moth to a fibre thread about five metres from the ground. Once the prey bats locked the target and sent out a foraging signal, they played the recorded interference signal. According to the records, the bat’s success rate of predation decreased by 73.5% compared with the situation without disturbance during predation. The team published its research today (6 November) on the website of the Journal Science.
Five years ago, Cochran and Connor said the moth could interfere with the hunting sonar of brown bats. But such competitive interference among individuals of the same species is the first to be found in the animal kingdom, they said.
Other researchers have previously heard similar sound signals from different types of bats, including male brown bats (big brown bats), and have suggested that such sounds may be used for cooperative foraging or to claim food ownership. “It’s obviously not about collaboration,” said Cynthia Moss, a neuroscientist at Johns Hopkins University in Baltimore, Maryland, whose team developed and adhered to the food claim hermeneutics.
“There is evidence to support both claims of statement and interference,” she said, noting that her team believes that the “timing of signals” approach adopted by Cochran and Connor, i.e., the continuous repetition of the terminal’s rapid foraging of sound waves, does not prove problematic. “Although this paper presents important conclusions, interesting and exciting, it is not the final conclusion.”
Nevertheless, the idea that bats not only have sonar, but also emit interference signals is still “cool,” Connor said. “We think engineers who can use both jamming sonar and radar are quite smart. But bats thought of it 65 million years ago.” Now, he and Cochran are wondering whether other echolocating species, such as dolphins, also have competitive disruptive effects.