They say that love makes your heart beat faster. Now, researchers have found that some mum’s hearts quicken when they hear their young calling.
The mums are Japanese house bats (Pipistrellus abramus), a social bunch that gather in communal maternity roosts to raise their young. At dusk, the mums head to out to forage, returning later to feed their youngsters milk, before snuggling down for the day.
Each mum can have up to four pups, and there can be dozens of families in a roost. Imagine then, trying to locate your own youngsters in a dark, cramped crèche full of hangry babies.
Not easy, but each pup has its own distinct isolation call, which the mother can recognise. Intrigued, researchers wondered how these calls were affecting the mothers’ physiology.
So, they captured four pregnant females and recorded the calls of their youngsters as they grew up. This included isolation calls, made by the pups at 2 days old, and echolocation calls, made by the pups at a month old. Then they played the sounds back to the mothers. The results are reported in Frontiers.
The mums were fitted with ECG monitors to record their heart activity. Their heart rates increased when they heard calls from their own pups, but not when they listened to the calls of other mothers’ youngsters.
“The fact that the mother’s strong heart rate increases in response to her own pup’s call suggests that these vocalizations instantly physiologically prime the mother to engage in maternal behaviour,” says Kazuki Yoshino-Hashizawa from Doshisha Univeristy.
Isolation calls from newborn pups typically signal distress, so it makes sense that the mothers’ arousal would increase. More surprising was their reaction to the echolocation calls of older pups. One explanation for this is that the mothers were simply more familiar with these more recent calls.
Researchers have found bat communication to be surprisingly rich. The winged mammals use calls to recognise one another, attract mates, defend food and roosting spots and protest against unwanted advances. Mother greater sac-winged bats even adjust the pitch and timbre of their calls when interacting with their pups, much like human parents use ‘motherese’ or ‘baby talk’.
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What we don’t know is how the change in heart rate feels to the mother bat. “While measuring overall heart rate allows us to gauge the intensity of physiological arousal, it cannot distinguish between positive emotions, such as maternal motivation, and negative ones, such as stress or alarm,” says Yoshino-Hashizawa.
So perhaps the mums’ hearts are racing with love. Or maybe they’re thinking, Oh no, not dinner time again!
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