Flush-pursuers fake out fleeing prey

Birds that advertise their presence to potential prey may improve their chances of catching a meal, a new study reports.

Most birds are stealthy when hunting insects, moving as little as possible to catch their would-be meals by surprise. A class of birds known as flush-pursuers, however, uses the movement of their conspicuously patterned tails and wings to elicit escape responses in nearby insects, such as flies. That deception leads to successful hunting. Now, biologist Piotr Jablonski at the University of Arizona in Tucson has figured out how this tactic works so well.

Earlier studies revealed that redstarts and other flush-pursers spread their wings and raise their tails to scare insects out of hiding.

This display drums up insects to pursue. That, in itself, makes for better hunting. But Jablonski has now shown that redstarts also trick insects into moving directly into the bird’s line of sight. The study appears in the May 22 Proceedings of the Royal Society of London B.

To pull off their trickery, the birds exploit a reflex of many insects. When flies sense motion, for example, they take an escape trajectory opposite to the source of motion. When pursued by a redstart, however, the insects are confused by the bird’s pronounced, flashy tail. They flee from it and, unwittingly, toward the bird’s head, becoming an easier target.

Jablonski credits the success of such tactics to the “rare-enemy effect.” They work because threats from unconventional predators, such as flush-pursuers, have been rare enough that the hunter’s prey haven’t evolved adequate escape tactics.