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Australia’s biggest bats fly thousands of kilometers a year—farther than wildebeest and caribou journey

Australia’s biggest bats—known as flying foxes—are among the world’s most restless nomads, according to a new study. Just how restless? The most peripatetic can journey up to 6000 kilometers per year, much farther than any land mammal and close to the distances covered by some whales and migrating birds.

This continent’s flying foxes can weigh up to 1 kilogram with meter-wide wing spans. But instead of hunting like other bats, they make nightly forays to flowers in search of nectar, pollen, and seeds. By day, they roost by the thousands in trees.

Researchers had thought these bats stayed local, loyal to a particular roost. But when they put satellite transmitters on 201 bats from three species in eastern Australia, they found they were mistaken: From months of tracking each bat, they calculated that the bats wandered anywhere from 1487 to 6073 kilometers per year, they report today in BMC Biology.

The black flying fox (Pteropus alecto) had the shortest range, followed by the gray-headed flying fox (P. poliocephalus­, above), and the little red flying fox (P. scapulatus). The little red flying fox averaged about 5000 kilometers per year—farther than champion mammalian migrators such as caribou, which travel 1200 kilometers per year, and wildebeest, which migrate 2900 kilometers with each trip.

Rather than following a seasonal path, flying foxes seem to wander randomly, most likely in search of newly flowering species. The little red flying fox, for example, travels 1300 kilometers north to south, but not continuously. Instead, it crisscrosses its range and settles briefly in dozens of different roosts, whose populations fluctuate based on the new migrants. In total, bats in the study visited 755 roosts, more than half of which were previously unknown to scientists.

Because these furry fliers are key to dispersing seeds and pollen, their meanderings help “connect” forests fragmented by fire or human activity, the researchers say. But their erratic, far-flung movements also complicate conservation and disease management, which is usually under the jurisdiction of local, not national, authorities. Now that researchers know nomadism is a way of life for these bats, they can start to search for some rhyme or reason to all this meandering.