Pregnancy may hamper bats’ ability to ‘see’ in the dark

Pregnancy can do weird things to the body. For some bats, it can hamper their ability to “see” the world around them.

Kuhl’s pipistrelle bats (Pipistrellus kuhlii) echolocate less frequently while pregnant, researchers report March 28 in BMC Biology. The change may make it harder for the tiny bats to detect prey and potential obstacles in the environment.

The study is among the first to show that pregnancy can shape how nonhuman mammals sense their surroundings, says Yossi Yovel, a neuroecologist at Tel Aviv University in Israel.

Nocturnal bats like Kuhl’s pipistrelles famously use sound to navigate and hunt prey in the dark (SN: 9/20/17). Their calls bounce off whatever is nearby and bats use the echoes to reconstruct what’s around them, a process aptly named echolocation. The faster a bat makes calls, the better it can make out its surroundings. But rapid-fire calling requires breathing deeply, which is something that pregnancy can get in the way of.

“Although I’ve never been pregnant, I know that when I eat a lot, it’s more difficult to breathe,” Yovel says. So pregnancy — which can add a full gram to a 7-gram Kuhl’s pipistrelle and may push up on the lungs — might hamper echolocation.

Yovel and colleagues tested their hypothesis by capturing 10 Kuhl’s pipistrelles, five of whom were pregnant, and training the bats to find and land on a platform. Recordings of the animals’ calls revealed that bats that weren’t pregnant made around 130 calls on average while searching for the platform. But bats that were pregnant made only around 110 calls, or 15 percent fewer.   

A decline in calls among pregnant bats could impede hunting, the team says. A computer simulation showed that the study’s expectant moms would catch 15 percent fewer insects than nonpregnant bats. That finding could help explain why some bat species chase after larger and slower prey once they become pregnant, focusing their energy on easier-to-spot food. Figuring out whether diminished echolocating ability is responsible for these diet shifts will require more fieldwork, Yovel says.

However, the idea that carrying a fetus would interfere with echolocation makes a lot of sense, says behavior ecologist Erin Gillam of North Dakota State University in Fargo. “As a mammal who has been pregnant, I don’t think these results are surprising at all.”