Sensory exploitation of prey: manipulation of the initial direction of prey escapes by a conspicuous 'rare enemy'

The painted redstart (Myioborus pictus) represents a group of non-cryptic p redators, the flush pursuers, who visually trigger prey escapes by spreadin g and pivoting their conspicuously patterned tails and wings. The prey are then chased in aerial pursuits. Such an exploitation of prey may be possibl e because the predation risk from redstarts is smaller than that from the p redatory guild of insectivores and their neural pathways are adapted to hel ping prey avoid common predators rather than 'rare enemies'. I propose that the pivoting movements of flush pursuers direct insect escapes across the central field of vision of a predator, where it is easier to track and inte rcept the prey. Eighty per cent of chases by wild redstarts were in a direc tion suggesting that prey were entering the birds' area of stereoscopic vis ion. The redstart's fanned and raised tail creates a stronger visual stimul us than a redstart's head. Flies escaped away from the section of the fly's field of vision in which the model's tail was located and towards the area where the predator's stereoscopic vision is likely to be located, in front of a bird's forehead. The experiments suggested that redstarts may not onl y exploit the sensitivity of typical neural escape pathways, which are non- directionally sensitive, but that they may also exploit the sensitivity of some directionally sensitive neural pathways in prey.