The effect of schedules of reinforcement on the composition of spontaneous and evoked black-capped chickadee calls

Abstract

Songbirds often modify elements of their songs or calls in particular social situations (e.g. song matching, flock convergence, etc.) but whether adult individuals also make vocal modifications in response to abiotic environmental factors (e.g. food availability) is relatively unknown. In the present study we test whether two different schedules of food reinforcement, fixed ratio continuous reinforcement and variable ratio partial reinforcement, cause adult black-capped chickadees to change the structure of their chick-a-dee calls. We also examine how these calls differ in two contexts: being alone versus when experiencing an alarming event. Wild-caught black-capped chickadees were housed in isolation to prevent social interaction and recorded weekly for seven weeks. Baseline recordings on week one show that calls given alone differed from those given during an alarming event in both note type composition and frequency (i.e. pitch). Calls also changed over time between birds on the two different schedules of reinforcement. In addition, birds on different reinforcement schedules responded differently during the two recording conditions. Our results suggest that call characteristics can be modified rapidly and may reflect abiotic environmental conditions. If call structure varies consistently with particular abiotic environmental conditions, much can be gained from bioacoustic analyses of calls from wild birds. However, vocal patterns must be consistent across dialects, and we must disentangle vocal changes due to the abiotic environment from those due to social interaction. Further research is needed from natural populations and across multiple regions.