Mother bats' hearts race at sound of their own pups

Researchers have discovered that mother Japanese house bats experience a significant increase in heart rate when they hear the distress calls of their own babies. This physiological response does not occur when the mothers hear calls from unrelated pups, suggesting a highly specific biological mechanism for recognizing kin within crowded colonies.

The study was inspired by observations in a laboratory colony where only biological mothers immediately rushed to retrieve separated pups. Lead author Dr. Kazuki Yoshino-Hashizawa from Doshisha University noted that while scientists knew pups emit acoustic distress signals, the internal reaction of the mother upon hearing these sounds remained unclear until now.

To investigate this phenomenon, the team monitored four pregnant bats captured near the university. Each mother gave birth to a litter of three pups. Scientists recorded isolation calls when the pups were two days old, using only male pups to eliminate variations based on sex. As the young bats matured, they began producing echolocation calls around eight days old and ceased making isolation cries by day twelve.

When the offspring reached forty days of age and could fly independently, researchers separated them from their mothers to conduct heart rate tests. The mothers were exposed to recordings of their own pups, unfamiliar pups, and an unknown adult male. The data revealed that heart rates spiked only in response to the vocalizations of their biological children.

Unexpectedly, the strongest cardiac reactions were triggered by the newer echolocation calls of the older, independent pups rather than the earlier isolation cries. Scientists hypothesize this may be due to the mothers being more familiar with the recent sounds, though further experiments are required to confirm this theory. The call of an unfamiliar adult male also caused a rapid heartbeat, which researchers suggest could indicate a perceived threat.

The authors acknowledge that the small sample size was necessary because caring for pregnant bats in captivity is difficult. They also noted that while heart rate measures the intensity of arousal, it cannot distinguish between positive emotions like maternal motivation and negative states such as stress. Future studies incorporating heart rate variability analysis may provide deeper insights into the emotional context of these vocal responses.