A new study led by Tel Aviv University (TAU) has found that pregnant bats experience a decline in their ability for spatial orientation and hunting, stemming from the fact that they produce about 20 percent fewer calls (the sounds that allow them to orient themselves via echolocation) and fly at a slower pace and lower altitude. These findings represent the first known evidence that pregnancy affects the sensory capabilities of mammals.
“At the peak of pregnancy, bats carry about 20 percent more than their normal body weight, and it is clear that this excess weight impacts their flying capacity. In this study, we wanted to check whether and to what extent pregnancy affects bats’ echolocation ability, their sonar,” said lead author Mor Taub, a research assistant in Zoology at TAU.
“Bats’ sonar is based on the emitting and receiving of strong and frequent sounds in order to map their surroundings. To make these sounds, bats, like us humans, need to transfer high-pressure air from the lungs through the vocal cords, or vocal membranes, which involves many muscles, such as the chest and diaphragm. We wanted to see if the excess weight from pregnancy affects the production of sounds.”
To test this, the scientists taught bats of the Kuhl’s pipistrelle species – a common species of bats in Israel that weigh only about six grams and feed mainly on mosquitoes – to search for and land on a small landing pad in the laboratory, and recorded the echolocation of both pregnant and non-pregnant bats. The analysis revealed that the rate at which pregnant bats emitted sounds was lower than that of the control group, with 20 percent larger intervals between each sound. Moreover, they flew slower and lower, an aspect likely to affect their hunting too.
“When a bat makes fewer calls, it gathers less information about the environment, its chance of colliding with objects increases, and its chance of finding food decreases — and this is at a time when the bat needs extra food to sustain the fetus in its womb,” explained senior author Yossi Yovel, an expert in Behavioral Neuroscience at TAU.
Previous studies have found that during their four-month long pregnancies, bats tend to change their diets. While scientists initially thought that this change was caused by their flying difficulties, the current findings suggest that it may also be due to their sensory difficulty in detecting certain types of prey.
“This is the only evidence we found in the professional literature showing that pregnancy affects mammals’ sensory abilities. We assume that there are similar cases in other species as well, but this is the first time that researchers have been able to measure and demonstrate the impairment empirically. Beyond the scientific interest, it is important to preserve mammal species in the wild, especially during pregnancy and newborn care, since animals are particularly vulnerable during this period,” Taub concluded.
The study is published in the journal BMC Biology.