While some animals that forage in groups are known to emit calls to attract others towards food, the FMB is used to repel, not attract, other bats.
"Despite decades of study, many things about common bat behaviors such as foraging remain mysterious," says Wright. "We were able to study a social call that is likely occurring thousands of times a night all over North America during the summer months, yet had not been described or studied before now."
The researchers discovered only male big brown bats emitted the FMB, possibly to advertise their dominance or claim their territory. Female bats did not emit FMBs. That may be because females form close associations with their roost mates and may forage near familiar individuals, while males often roost alone or in small bachelor colonies and may be less familiar with others foraging nearby.