Wednesday, April 16, 2008

Butterfly 'blinks' scare predatory birds

18 June 2005

BLUFFING, the oldest trick in the poker-player's book, comes in rather handy in the natural world, too.

The peacock butterfly, a perfectly tasty snack for a bird, often cheats death with what is nothing more than a bluff. Suddenly exposing the prominent eyespots on the butterfly's wings is enough to startle a foraging bird and save the insect's life, says Adrian Vallin, a zoologist at Stockholm University, Sweden.

Though butterfly eyespots have long been assumed to be an anti-predator defence, there has been little experimental evidence to support this. Vallin and colleagues tested the idea by blacking out the eyespots of peacock butterflies (Inachis io) with a marker pen, and putting them at the mercy of blue tit predators. They found that while 13 out of 20 butterflies treated this way were eaten by the birds, only one out of 34 butterflies with intact eyespots succumbed (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2004.3034).

The big question is why birds don't learn to recognise a harmless little butterfly. It is likely that the consequences of calling its bluff are too dire, says Graeme Ruxton, an ecologist at the University of Glasgow, UK. It might mean being eaten by a predator such as an owl. "Blue tits are generalists, and tend to err on the side of caution," he says.



Butterfly 'stare' doesn't intimidate birds

08 March 2008

NO ONE likes being stared at. It has long been assumed that the eyespots of butterflies and moths tap into just that fear, but the true function of such wing patterns might be much simpler.

Martin Stevens at the University of Cambridge and colleagues made fake butterflies with a range of patterns on their wings. Some were round and "eye-like", others had square or barred patterns. They placed the fake insects in woodland, then recorded any bird attacks on them. The team thought that if eyespots function as a deterrent because they look like eyes then the butterflies with eye-like shapes should be attacked less. In fact, butterflies with eyespots survived no better than those with other obvious shapes. However, butterflies with the largest markings, regardless of shape, suffered 30 per cent fewer attacks (Behavioral Ecology, DOI: 10.1093/beheco/arm162). Conspicuousness, the team conclude, not eye mimicry, is what deters predators.

"Predators tend to stay away from highly conspicuous prey, possibly because most conspicuous objects in nature are toxic," says Stevens. "We think this is the primary eyespot effect." Eyespots in other animals probably did evolve to mimic eyes, the team notes. Hawkmoth caterpillars use eyespots to mimic snakes, for example.