Meeting Abstract
The performance of courtship displays varies greatly among and within individuals of a species. Within individuals, displays can vary in quantity and quality throughout a bout, day or season and some individuals are faster, more coordinated or more consistent than others. Intra- and inter-individual variation in birdsong has been studied heavily, but comparable studies of non-vocal courtship displays in birds remain relatively rare. Over the past 9 years, we have studied courtship in ruffed grouse (Bonasa umbellus), a gamebird species that produces a wingbeating display known as drumming. Here, we test whether males vary their drumming display within a season and to what extent that variation reflects body size. Generalized additive mixed models revealed that male ruffed grouse increase their drumming speed daily to reach a maximum rate by mid-morning, which is then maintained throughout the day. This change in performance follows an overnight cessation of activity and low temperatures, suggesting that this increase in drumming speed reflects a daily warm-up period. Comparisons with morphometric measurements revealed that the maximum daily drumming speed varies inversely with body mass; larger males drum slower than smaller males. This inverse relationship is likely due in part to pectoral muscle mass, which comprises one third of male body mass and varies seasonally in association with drumming activity. Based on our findings, we propose that warm-up periods are a common feature of avian courtship displays and further studies are needed across species that vary in the diversity of motor acts that are produced within displays.
