Sunday, April 10, 2011

Caterpillars outsmart birds

Yes, they are smart enough to beat birds. Caterpillars that masquerade as twigs to avoid becoming a bird's dinner are actually using clever behavioural strategies to outwit their predators, a new study reveals.

Dr. John Skelhorn, a lecturer in animal behaviour at the University of Exeter, said: "The caterpillars are not just blindly mimicking inedible objects in the environment and hoping for the best, they are actually using complex habitat-selection strategies which exploit predators' hunting behaviour. According to the study, twig mimicking ‘Early Thorn moth’ caterpillars (Selenia dentaria) choose their location to maximise their chances of fooling their predators into thinking they are twigs.

Using domestic chicks (gallus gallus domesticus) as predators of the caterpillars, research showed that caterpillars are more likely to fool birds when twigs are common. In order to exploit birds' behaviour, caterpillars position themselves in locations where twigs are in abundance during the day -- even if they're not good locations for feeding. At night, when the predators cannot hunt by sight, the caterpillars go to rich feeding grounds -- regardless of twig abundance.

Study reveals that chicks are less likely to search for masquerading prey when the object they mimic, in this case twigs, is in abundance.

"The caterpillars make the most of this by selecting habitats where twigs are common during the day, but then abandon them at night, when there are no visually-hunting predators around, in order to go in search of the best feeding grounds."

When the caterpillars were given two options; one with few twigs but plenty of food, and another with more twigs but no food, Caterpillars showed a strong preference for the branch with lots of twigs, offering the best protection from their predators, during the daylight. At night, they opted for the food-rich branch.


John Skelhorn, Hannah M. Rowland, Jon Delf, Michael P. Speed, Graeme D. Ruxton. Density-dependent predation influences the evolution and behavior of masquerading prey. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1014629108