Environmental variables predict timing of breeding in the polygynous Eurasian bittern Botaurus stellaris

Abstract

The timing of clutch initiation in migratory birds is determined by many factors and affects fitness. In polygynous species the date of egg laying may also be determined by mating status. In order to identify the habitat factors enabling Eurasian bittern females to breed early, a study was carried out on nine fishpond complexes in eastern Poland during 2003-2009. The habitat characteristics of the nesting sites, including fish stock type and the breeding success were recorded for 48 monogamous, 31 primary, 30 second and 12 third or fourth females. The analysis showed that early nesting females preferred a higher density of old reed stems and chose less attractive ponds with poorer food resources. Monogamous and primary females laid first eggs eight days earlier on average and had higher breeding success than the second, third and fourth females. The relationship between the fate of broods and the breeding success of neighbouring nests was found for second females. Our results suggest that Eurasian bittern females benefit from early nesting, provided they can find appropriate vegetation at the nesting site.