Research reveals the city’s surprising effect on birth timing.

A groundbreaking study from Tel Aviv University, the first of its kind on mammals, has found that bats living in urban environments give birth, on average, about 2.5 weeks earlier than bats living in rural areas. The researchers attribute this difference in birthing times between the city and the countryside to more favorable temperatures and greater food abundance in urban areas. Bats are mammals, making this the first study to link the urban living environment to the timing of birth in mammals.

The research was led by the lab team of Prof. Yossi Yovel from the School of Zoology in the Wise Faculty of Life Sciences and the Steinhardt Museum of Natural History at Tel Aviv University. The study included contributions from Dr. Maya Weinberg, Dean Zigdon, and Mor Taub, and was published in the scientific journal BMC Biology.

Prof. Yossi Yovel.

Over three years, the researchers monitored ten bat colonies in urban and rural areas, sampling hundreds of female bats and approximately 120 pups from these colonies. The findings revealed that pups born in urban colonies were, on average, 2.5 weeks older, as evidenced by their longer forearms and higher body weights compared to pups from rural colonies.

Prof. Yovel explains: “Fruit bats living in cities benefit from favorable environmental conditions, including higher temperatures due to the ‘urban heat island’ effect and greater food availability, primarily from ornamental fruit trees irrigated year-round. These conditions allow urban bats to cope better with harsh winters and start their reproductive cycles earlier. This enables females to give birth earlier in the season, increasing their chances of becoming pregnant again within the same year.”

However, the researchers emphasize that it remains unclear whether the bats are shortening their pregnancies (a capability known in some bat species) or becoming pregnant earlier. They add that the study opens the door to further research on how urbanization affects mammalian reproductive patterns in general and bats in particular, and how these findings can be used to protect other species in changing ecosystems. “This study highlights the importance of understanding the connection between animals and their environments, especially in an era when urbanization is reshaping the planet,” concludes Prof. Yovel.

A mother bat in flight, carrying her pup beneath her in the city and countryside (Photo credit: Yuval Barkai).