Predator versus prey: on aerial hunting and escape strategies in birds

Predator and prey attack-escape performance is Likely to be the outcome of an evolutionary arms race, Predatory birds are typically larger than their prey suggesting different flight performances. We analyze three idealized a ttack-escape situations between predatory and prey birds: climbing flight e scape, horizontal speeding, and turning and escape by diving. Generally a s maller bird will outclimb a larger predator and hence outclimbing should be a common escape strategy. However, some predators such as the Eleonora's f alcon (Falco eleonorae) has a very high rate of climb for its size. Prey sp ecies with an equal or higher capacity to climb fast, such as the swift Apu s apus, usually adopt climbing escape when attacked by Eleonora's falcons. To analyze the outcome of the turning gambit between predator and prey we u se a Howland diagram, where the relative linear top speeds and minimum turn ing radii of prey and predator define the escape and danger zones. Applied to die Eleonora's falcon and some potential prey species, this analysis ind icates that the falcon usually wins against the example prey species; that is, the prey will be captured. Level maneuvering hunting is the most common strategy seen in Eleonora's falcons. To avoid capture via use of this stra tegy by a predator, the prey should be able to initiate tight turns at high linear speed, which is facilitated by a low wing loading (weight per unit of wing area). High diving speed is favored by large size. Lf close enough to safe cover, a prey might still opt for a vertical dive to escape in spit e of lower terminal diving speed than that of the predator. On the basis of aerodynamic considerations we discuss escape flight strategies in birds in relation to morphological adaptations.