Extra-pair copulations of grey heron Ardea cinerea in Arcachon Bay (SW France)

Abstract

In a colony of grey heron Ardea cinerea, located on the French Atlantic coast (Arcachon Bay), the copulatory behaviour of herons was observed during two breeding periods (1992 and 1993). A total of 181 intra-pair copulation attempts and 11 extra-pair copulation attempts (5.7% of all copulation attempts) were observed. Eighty-nine percent of the intra-pair copulation attempts and 54.5% of extra-pair copulation attempts were successful. Ten of eleven male herons involved in extra-pair copulation attempts were paired and had their nests close to the target female nests. Only one male involved in EPCAs was unmated. In two cases of extra-pair copulation attempts, the target females deserted the nest after the attempt, during their egg-laying period (the most important fertile period). All extra-pair copulations were made during the egg-laying period of the target females and during both incubation and guardian periods of the males.