Despite their exceptional vision, one city-dwelling colony of fruit bats echolocates throughout the day, something specialists had not expected.
Researchers report in the April 11 issue of Current Biology that a population of Egyptian fruit bats (Rousettus aegyptiacus) in downtown Tel Aviv utilises sound to navigate throughout the day. The discovery significantly increases the time that bats from this colony echolocate. Some team members had spotted bats clicking while flying in low-light circumstances a few years earlier. Even though the bats can see very well, the noon sound-off appears to aid foraging and navigation.
It’s rare to see bats active during the day. Only around ten of the more than 1,400 species are diurnal. Furthermore, during the day, most diurnal bats do not utilise echolocation, instead depending on their eyesight to feed and avoid obstacles. They conserve echolocation for low light or complete darkness.
That’s why a group of Tel Aviv researchers were taken aback two years ago when they spotted a bat smiling during the day. They were going over images from their most recent research of Egyptian fruit bats when they came across one with its jaws slightly apart and upwards.
“When an Egyptian fruit bat smiles, he’s echolocating,” explains Ofri Eitan, a bat researcher at Tel Aviv University. “He’s creating clicks with his tongue and his mouth is wide.” “However, this was during the day, and these bats have excellent vision.”
Many of the other images Eitan and his colleagues looked at — many of them — showed happy bats in broad daylight. The researchers demonstrated in 2015 that diurnal Egyptian fruit bats utilise echolocation outside, at least occasionally, under diverse low light circumstances. However, the researchers did not investigate whether the bats were echolocating during the peak light hours of the day.
The researchers began to question how unusual this conduct was. The team says, “We expected that fruit bats would seldom utilise echolocation in broad daylight.”
As a result, the researchers focused their camera and audio recording equipment on their research colony, which roosts on the ceiling of a mall’s subterranean parking lot in Tel Aviv. The researchers had to accept they were mistaken after filming about 500 flying bats. As they emerged from their colony, just over 70% of the bats used echolocation on a regular basis.
Eitan recalls, “We were startled to witness that.” “OK, so the bats are echolocating,” says the narrator. Is it, however, functional?”
The researchers next investigated whether bats utilised echolocation when hunting, flying near and landing on fruit trees, and visiting an artificial pool to drink. The bats all echolocated, according to the researchers, some even with enormous portions of fruit in their jaws.
Before landing on a limb or approaching the pool, the bats boosted their click rates substantially. To put it another way, the bats were upping their game as they approached dangerous objects in order to avoid colliding with them or landing awkwardly.
The researchers add, “We indicate that echolocation gives higher distance prediction accuracy than eyesight, making it beneficial while flying near impediments such as trees or descending to drink.”
Previous study by the scientists also found that when bats fly far above the ground with no obstacles, they seldom grin or click, implying that they may turn off their echolocation when it isn’t needed.
Most bat specialists think that these animals evolved to remain mostly nocturnal in order to escape visible predators like birds of prey. But, according to Danilo Russo, a bat researcher at the University of Naples Federico II in Italy who was not involved in the study, “observations like this one tell us that echolocation must be so hard-wired in bats that it keeps being employed even when their keen eyes would suffice.” “This is particularly fascinating in the study’s species, which still rely on eyesight in addition to echolocation.”