University of Missouri

An ecologist marvels at animals that learn to eavesdrop.

All through college I resisted getting glasses, but I finally succumbed for my first field trip to Peru; I was determined to see everything. Upon arrival, however, I realized that good vision was scarcely enough. One morning, I walked through the forest with an ornithologist, the late Ted Parker, famed for having learned the songs of thousands of birds. Although we saw few of the singers, he knew the source of each fluted phrase, monotonous chant and raucous outburst.

Attending to the signals of other species — visual, auditory and so on — is useful not only to ecologists, but also to the predators that eavesdrop on their prey. In some cases, such behaviour is hard-wired; however, this seems unlikely for species that exploit a wide range of prey.

Recent research has revealed a more flexible strategy. Martinus Huigens of Wageningen University in the Netherlands and his colleagues studied a tiny wasp that parasitizes butterfly eggs (M. E. Huigens et al. Proc. Natl Acad. Sci. USA 106, 820–825; 2009). The wasp, Trichogramma evanescens, learns, after a single experience, to exploit the hosts' chemical-communication system to find and hitchhike on a mated female, disembarking when the butterfly lays her eggs.

Prior research had revealed only one other such case, in the bat Trachops cirrhosus, which learns the calls of poisonous and edible frogs (R. A. Page and M. J. Ryan Curr. Biol. 16, 1201–1205; 2006).

These examples suggest that learning which communicative signals to follow may be a common feature of the evolutionary race between predator and prey. It is doubtful that any bat or wasp can retain as many signals as a legendary ornithologist, but it seems that the drive to learn them has a long history.