THE ANTIPREDATOR VOCALIZATIONS OF ADULT EASTERN SCREECH-OWLS

Adult eastern screech-owls (Otus asio) used six different vocalizations (bounce songs, whinny songs, bark calls, bark-screech calls, screech calls, and bill-claps) during trials in which a human approached nest sites or approached and handled nearly-fledged or recently-fledged young. Bounce songs and whinny songs were uttered more frequently during nest defense trials while bark calls, screech calls and bill-claps were uttered more frequently during trials with young owls. We suggest that bounce and whinny songs serve as low-intensity warnings to mates and nestlings. Bark calls consisted of a single, short duration note and appear to serve as warning calls, informing a mate and young of an approaching predator and informing the predator of a willingness to attack. Screech calls were short duration, high volume calls. Most screech calls were given during flights directed at the predator, and may function as a high-intensity warning call. Bark-screech calls appeared intermediate to bark and screech calls, both in structure and function. Most bill-claps were given during flights directed at the predator, often in conjunction with screech calls. We suggest that the combined vocal signal of screech calls and bill-claps represents the highest-intensity vocal warning directed at potential predators by screech-owls.