Calling in the face of danger: Do nestling Red-winged Blackbirds (Agelaius phoeniceus) suppress begging in response to predator playbacks?

Abstract

ABSTRACT Nest predation is the most frequent cause of nest failure in birds such as the Red-winged Blackbird (Agelaius phoeniceus) that nest on or near the substrate. Nestlings should therefore exhibit adaptations to reduce the risk of nest predation. We tested the nestling antipredator hypothesis by examining the begging responses of Red-winged Blackbird nestlings to vocalizations of (1) an important nest predator (American Crow, Corvus brachyrhynchos), (2) a predator that rarely preys on nestlings (Cooper's Hawk, Accipiter cooperii), and (3) a nonpredator (Northern Flicker, Colaptes auratus). We performed playbacks with (1) both parents present at the nest, (2) male at the nest, and (3) neither parent present. Following playback, we measured duration of nestling begging after the parent departed (begging persistence), bouts of otherwise normal begging when no parent was present (parent-absent begging), and calling without postural components of begging (nonpostural begging). When the male or both parents were present during playback, adults responded with alarm calls and nestlings significantly reduced parent-absent begging following American Crow and Cooper's Hawk playbacks. Nonpostural begging was significantly reduced following Cooper's Hawk playback, but there were no significant differences in the other begging variables. When neither parent was present, we found no significant differences in nonpostural begging in response to the 3 playback types, but parent-absent begging was significantly reduced following American Crow and Cooper's Hawk playbacks when compared to Northern Flicker playbacks. These results show that nestlings suppress their vocal begging in response to calls of predators including Cooper's Hawks even though they are not common nest predators.