Counting Africa’s largest bat colony

by Carla Avolio, Max Planck Society
June 30, 2023

Once a year, a small forest in Zambia becomes the site of one of the world’s greatest natural spectacles. In November, straw-colored fruit bats migrate from across the African continent to a patch of trees in Kasanka National Park. For reasons not yet known, the bats converge for three months in a small area of the park, forming the largest colony of bats anywhere in Africa. The exact number of bats in this colony, however, has never been known. Estimates range anywhere from one to ten million. A new method developed by the Max Planck Institute of Animal Behavior has counted the colony with the greatest accuracy yet. The method uses GoPro cameras to record bats and then applies artificial intelligence (AI) to detect animals without the need for human observers. The method produced an overall estimate of between 750,000 and 1,000,000 bats in Kasanka — making the colony the largest for bats by biomass anywhere in the world.

“We’ve shown that cheap cameras, combined with AI, can be used to monitor large animal populations in ways that would otherwise be impossible,” says Ben Koger who is first author on the paper. “This approach will change what we know about the natural world and how we work to maintain it in the face of rapid human development and climate change.”

Even amongst the charismatic fauna of the African continent, the straw-colored fruit bat shines bright. By some estimates, it’s the most abundant mammal anywhere on the continent. And, by traveling up to two thousand kilometers every year, it’s also the most extreme long-distance migrant of any flying fox. From an environmental perspective, these merits matter a lot. By dispersing seeds as they fly over vast distances, the fruit bats are cardinal reforesters of degraded land – making them a “keystone” species on the African continent.

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