Hormonal responses to removal of a breeding male in the cooperatively breeding white-browed sparrow weaver, Plocepasser mahali

Abstract

The white-browed sparrow weaver ( Plocepasser mahali) is a cooperatively breeding Ploceid finch that lives in groups of up to 11 individuals. Each group consists of a dominant breeding male and female and a varying number of nonreproductive birds that help feed young and defend the group territory. Experimental removal of the dominant male resulted in attempts by other males to take over the group. Removal of a subordinate, nonbreeding male, as a control, resulted in no change of status among group members. During takeover, there was a transitory increase in plasma levels of luteinizing hormone in the new dominant male, but no change in testosterone levels. As reported in previous investigations, dominant males tended to have higher levels of testosterone than females or subordinate males, but this was not related to the heightened aggression of the takeover. Plasma levels of luteinizing hormone, testosterone, and corticosterone did not differ between the other status groups. The possibility that luteinizing hormone, or a hitherto unidentified androgen, may regulate aggression in the white-browed sparrow weaver is discussed.