Social and life-history correlates of hormonal partner compatibility in greylag geese (Anser anser)

In long-term monogamous birds reproductive success varies considerably among pairs. Determinants of reproductive success may be individual as well as pair-specific parameters, including the degree of compatibility and coordination among pair partners. However, little is known about the consistency of partner compatibility with regards to social contexts and life-history changes. In the long-term monogamous, biparental greylag geese, reproductive success was previously found to correlate positively with the degree of hormonal compatibility within pairs. In the present study, we analyzed the degree of within-pair testosterone covariation (TC) in relation to individual and pair-specific life history and social instability. We found that greylag goose pairs facing active social challenge had lower degrees of TC than those in unchallenged pair-bonds, whereas the permanent attachment of a third individual to an existing pair or the number of previous partners did not correspond with changed TC. Furthermore, TC decreased with increasing pair-bond duration and increased with female age but was not related with age of the male partner or other life-history parameters. Hence, our data suggest that hormonal partner compatibility in greylag geese is not a stable trait, but rather reflects a pair's status quo, which may be particularly affected by the stability of the social environment. Copyright 2009, Oxford University Press.