Display Repertoire Shifts and "Extramarital" Courtship in Herons

Abstract

The display repertoires of courting Great Blue Herons and Great Egrets change as the social contexts progress toward pair-formation. These context shifts have been organized into chronological stages: (1) Solo Stage - when the male is alone on the nest and displaying to the colony at large, (2) Bachelor Stage - when the unpaired male is communicating with particular females, (3) Paired Stage - when the male has accepted one female on his nest, and (4) No-mate Stage - when the newly paired male is alone on the nest and resumes courtship. The displays most frequently used in each stage are assumed to serve the individual's primary task, as inferred from the general context. For example, the Stretch display is most common when unpaired males are trying to induce females to approach : thus it seems to have a female-attracting function. Extramarital male courtship during the No-mate Stage begins whenever his new mate leaves to forage and lasts only 1-2 days. The no-mate male's display repertoire is identical to a courtship pattern: his behaviour resembles normal pair-formation in every way. I believe such courtship to be a male strategy for protecting his previous courtship investment from desertion by the female (divorce insurance). He courts new females and sometimes partially forms new pairbonds by the time his mate returns. Presumably these bonds develop fully if the initial mate actually does desert him. Two other possible explanations for extramarital courtship - extra copulations and polygyny - were not observed in the field and are considered theoretically unlikely.