Extra-pair copulations of Grey Herons nesting at high densities

Grey Heron (Ardea cinerea) Science Article 2


The copulatory behaviour of Grey Heron Ardea cinerea was observed in a colony in Donana (SW Spain) during two years. A total of 262 pair copulation attempts (PCAs) and 39 extra-pair copulation attempts (EPCAs) (12.9% of all copulation attempts) were observed among 31 focal pairs. 84% of PCAs and 50% of EPCAs resulted in cloacal contact. Eleven males (35%) and 19 (61%) females were involved in EPCAs. There was a correlation between the time that female spent alone on the nest and the occurrence of EPCAs during the presumed fertile period of the female. The incidence of EPCAs observed at Donana was greater than reported for the species in other localities, and could be explained by more opportunities for promiscuous behaviour at high densities. Data provided by this study support the conclusion that mate guarding and PC frequency are mechanisms of paternity defense under the sperm competition hypothesis.

Ramo C., ARDEA 81 (2): 115-120.

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