A Rare Observation of Adopting Unrelated Pup.

• Position: VAMPIRE BATS

The death of a vampire bat 19 days after giving birth presented scientists studying the animals with an unexpected chance to observe a rare event: a female bat's adoption of an unrelated baby.

The researchers had captured common vampire bats in Panama as part of ongoing studies of the formation of cooperative relationships among strangers. The team used infrared surveillance cameras to observe six hours of activity spaced over the span of each day.

Two unrelated and unfamiliar female bats were observed forming a social bond based on mutual grooming and food sharing that increased over time. The researchers had named them BD and Lilith.

Lilith gave birth to a female pup about five weeks after the bats first met in captivity. As Lilith grew ill and spent less time caring for her pup, BD picked up the slack and even appeared to start nursing the baby. After Lilith died, BD adopted the pup, consistently nursing, grooming, and sharing blood meals with the baby with almost no assistance from other adults in the colony.

"It's really cool that the little pup was adopted by the mother's closest social partner," says lead author Imran Razik, a graduate student at Ohio State University, Columbus, who works in the lab of senior author Gerald Carter, assistant professor of evolution, ecology...