Israeli scientists discover how bat moms teach young to navigate

Process, tracked by sensors attached to animals, includes dropping pups off at ‘nursery’ trees while mother forages for food

Sue Surkes is The Times of Israel's environment reporter.

A female Egyptian fruit bat leaves the cave with her pup attached underneath (Yuval Barkai)
A female Egyptian fruit bat leaves the cave with her pup attached underneath (Yuval Barkai)

Tiny sensors attached to Egyptian fruit bats have enabled Tel Aviv University researchers to understand for the first time how bat mothers teach their pups to navigate.

Initially, the pup flies with the mother — suspended upside down, eyes open, and suckling — as she forages for food.

When junior reaches three weeks, mom starts to drop it off every night at the same tree, located within a kilometer of their home cave.

She leaves the pup at the tree — usually an evergreen one for maximum camouflage — either alone or with other bat babies. She will pop back during the night to provide a quick feed before flying off again to forage, finally returning to the tree to pick baby up and get home before sunrise.

Gradually, the pup starts to experiment by flying from the “nursery” to nearby trees, gaining confidence, and flying ever farther, before returning to wait for the mother.

As the pup grows bigger, heavier, and harder to carry, mom drops it at a tree closer to the cave.

A bat pup waiting for its mum in a ‘nursery’ tree. (Aya Goldshtein)

On reaching eight to ten weeks, the pup leaves the cave alone and flies independently, starting at sites it has previously been dropped off at.

But mom is still there, supervising.

According to the research, published in the peer-reviewed journal Current Biology, “thanks to the mothers’ behavior, the pups are exposed to situations allowing them to learn to navigate to specific trees, flying along the similar paths used by the mothers while transporting them, and to learn to return home on time.”

The researchers attached tiny GPS devices, as well as accelerometers that measure wing movements, to both mothers and pups, and tracked both simultaneously. The study forms part of more long-term research into fruit bats being led by Prof. Yossi Yovel of the Department of Zoology at TAU’s Faculty of Life Sciences.

Aya Goldshtein (left) and Lee Harten. (Tel Aviv University)

“We believe that the ‘nursery’ tree is chosen by the mother as a starting point, an anchor not too far from home, from which the pup can navigate to other places,” explained Dr. Lee Harten, one of the researchers. “The tree also serves as a meeting place for mother and pup if the little one happens to get lost.”

Said co-researcher Dr. Aya Goldshtein, “At the next stage of the process, mom leaves her pup in the cave, expecting it to come out on its own. If it shows no such initiative, she goes back to the previous stage and carries it to the ‘nursery.’

“In addition, at night’s end, she makes sure that the pup has made it back home, and if the pup is late, she looks for it at the ‘nursery’ tree and helps it find its way to the cave.

“At the final stage, starting around the age of ten weeks, the pup is already independent, searching for food on its own every night. To begin with, it flies to the familiar ‘nursery’ tree, then goes on to nearby trees, gradually expanding its circle of navigation.”

Bat lab researchers in the field. (Tel Aviv University)

According to Prof. Yovel, “Many animals must become independent at a very young age to survive.

“For flying animals, the ability to navigate on their own to sources of food is an essential aspect of independence. Thus, for example, young fruit bats, which were the focus of the study, are required to navigate every night over long distances — sometimes dozens of kilometers — to reach a specific tree or group of trees where edible fruit can be found,” he added.

“Even when they succeed, they still face the challenge of finding their way back home to their colony’s cave. In our study, we wanted to find out how they learn to do this.”

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