Habitat quality and breeding parameters in relation to female mating status in the polygynous Eurasian Bittern Botaurus stellaris

Abstract

The Eurasian Bittern Botaurus stellaris has a polygynous mating system where the nests of solitary and clumped females are located within a male territory. However, the factors that may favour the formation of nest clusters remain unknown. The focus was on the clustering effect in the Eurasian Bittern population on fishpond complexes in eastern Poland in order to test whether clumped nesting is dependent on habitat quality. Breeding parameters were also assessed in order to investigate the advantages accruing to females of nesting close together in clusters. During the breeding periods between 2003 and 2009, we found 144 active nests of the Eurasian Bittern: most of them (55.5 %) were in clusters of two to four nests. The mean distance between adjacent nests in a cluster was 23.5 m. The proportion of open water to emergent vegetation and the category of fish stock have significant effects on cluster nesting in the Eurasian Bittern. There were differences between single and clumped nests with respect to the first-egg laying date and male presence. The environmental and ecological factors that may determine the Eurasian Bittern female’s nest-site choice are discussed.