It took more than a year for them to have enough data to realize that their initial results were not a mistake. The signals from mother and baby bats had disintegrated as the mothers carefully dumped their babies into trees as they searched for food.
“We couldn’t imagine that the mother would just leave a puppy in a tree,” said Dr. goldshtein.
After five years of fieldwork, they got a clear picture of what was going on. When the pups of Egyptian fruit bats are a few weeks old, mothers carry them out of the cave at the beginning of the night, as usual, then fly to a tree and leave them – a sort of daycare, unsupervised. The mother comes back all night, perhaps to nurse and warm up the puppy. When she is done foraging, she carries the pup home.
The mother uses the same tree, or a few trees, over and over. As the pup gets older and heavier, the mother shifts to a drop-off tree closer to the cave.
Then, when the puppy is about 10 weeks old, the mother leaves the cave, alone. The young bat emerges from the cave for its first solo journey – and although there are thousands of trees nearby, it flies straight to its most recent drop-off site. As he gets older, the pup uses the drop-off tree as a starting point for his own exploration.
“We were amazed to see these results,” said Dr. goldshtein. Somehow, while hanging from their mother’s belly, bats learn their way. The authors are not exactly sure how this learning happens. They think it’s by sight, although Egyptian fruit bats can echolocate with clicks of their tongues.
Mirjam Knörnschild, a behavioral ecologist at the Natural History Museum in Berlin who studies bats, said the authors had done “amazing work” unearthing the poorly understood interactions between mother bats and pups. “The results strongly suggest that mothers actively help their pups with orientation,” she said.
dr. Knörnschild was surprised that puppies can memorize these routes while carried upside down and without flying the routes themselves. “Personally,” she said, “I think it’s amazing.”