BULLFROGS know a familiar voice when they hear it. When defending their territory, North American male bullfrogs listen for subtle differences in the croaks of other males to sort out the newcomers from the old-timers.
Using synthetic frog sounds, biologists Mark Bee and Carl Gerhardt of the University of Missouri-Columbia played male bullfrogs familiar and unfamiliar croaks. The frogs reacted more aggressively towards the calls of strangers, whether they came from previously occupied territories or from new locations (Proceedings of the Royal Society B, DOI 10.1098/rspb.2002.2041). That means the frogs can recognise individual voices regardless of location, say the…
