Information Exploitation By Downy Woodpeckers in Mixed-Species Flocks

Abstract

Downy woodpeckers (Picoides pubescens) benefit from foraging in mixed-species winter flocks by decreasing their vigilance level and increasing their feeding rate. I investigated one mechanism, auditory cues, downy woodpeckers use to obtain information on the presence of other flock members and potential predators. Experiments with predator models and with recorded alarm calls and contact calls from flock members yielded the following results. Downy woodpeckers use the contact calls of other flock members to assess the presence of flocks members. Woodpeckers foraging alone but with the recorded contact calls of flock members showed lower vigilance levels and higher feeding rates than woodpeckers foraging alone with no recordings or with the control recordings. Woodpeckers respond to the other species' alarm calls as an indication of potential predators and also to their contact calls as an all clear signal afterwards. Downy woodpeckers decreased their vigilance levels and resumed foraging faster when the contact calls followed the presentation of predator models or alarm calls than when these were presented alone.