The short version
- Mother Japanese house bats’ heart rates rose when they heard recordings of their own pups, and not when they heard other bats’ pups.
- The biggest jump came from their pups’ echolocation calls at a month old, more than from the cries the pups made at two days.
- The study had only four mothers, and heart rate shows arousal without saying whether the feeling is good or bad.
Researchers at Doshisha University in Japan fitted four mother Japanese house bats with heart monitors and played them recordings. Each mother had raised a litter of three. When they heard their own pups’ echolocation calls, recorded at about a month old, their heart rates rose by an average of about 51 beats a minute from a resting rate of roughly 200 to 300. Their own pups’ isolation cries, recorded at two days old, raised it by about 18. The same kinds of calls from other mothers’ pups made no significant difference. The paper was published on October 23 in Frontiers in Ethology.
One result surprised the team. The echolocation call of an unfamiliar adult also raised the mothers’ heart rates sharply, and the paper does not explain why. The authors suggest the mothers reacted most to their pups’ older calls because those were the calls they had heard most recently, but pup age and call type were tangled together in the design, so that idea is untested.
The sample is tiny, four mothers from one colony, and one died partway through. Heart rate alone, as lead author Kazuki Yoshino-Hashizawa told Phys.org, “cannot distinguish between positive emotions, such as maternal motivation, and negative ones.” The finding is that the mothers’ bodies told their own pups’ voices from others’, and not what they felt.
