MIGRATORY bats have smaller brains than their stay-at-home cousins, suggesting they cannot afford the luxury of lugging large, energetically expensive brains on long journeys. The discovery might also be true for birds.
The brains of migratory birds tend to be smaller than those of similar-sized species that do not migrate. But biologists have been unsure whether this is because non-migratory birds need larger brains to cope with the challenges of finding food through the changing seasons, or because migrators need to pare down their weight for travel. Larger brains burn more energy and their extra weight makes flight more costly too.
, an ecologist at the University of Western Ontario in London, Canada, and his colleague of the University of Southern Denmark in Odense turned to bats for the answer. Non-migratory species of bat typically hibernate through the winter months, so they do not need to adjust their foraging behaviour to survive. Yet the researchers still found that migratory bats had smaller brains than non-migratory ones (Biology Letters, ).
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Other factors may also be important in birds, which show a greater difference in brain size than bats. But the finding suggests that the need to reduce weight in migrators is a sufficient evolutionary force to drive some of the difference.
