Nest and mate choice in the red bishop (Euplectes orix) : female settlement rules

Abstract

We investigated female settlement in a colony of red bishops (Euplectes orix), a territorial and highly polygynous weaverbird widely distributed over sub-Saharan Africa. An earlier study showed that male reproductive success is mainly determined by the number of nests a male builds in his territory, which appeared to be a good indicator of male quality. Because males provide no parental care or food resources within the territory, females sharing a territory do not compete for material resources and might therefore be expected to settle preferentially in territories of males that build many nests to gain the possible genetic benefit of high-quality offspring. An analysis of female settlement, however, revealed that females did not show a preference for territories of males with many nests and that the distribution of female breeding attempts with regard to the number of vacant nests within a territory could be explained best by random female settlement in 3 out of 4 years. Females settled more often than expected by chance (in 3 out of 4 years) in territories already containing occupied nests, indicating that resident females did not discourage settlement of additional females. However, sharing a territory with other females might impose costs in terms of an increased predation risk because nests in territories that contained other nests with young suffered from higher predation than nests in territories that did not contain other nests with young. Females therefore might trade the possible benefits of settling in territories of males with many nests against the costs of sharing a territory with other females. This might result in the mating pattern found with random female settlement and male reproductive success being directly proportional to the number of nests built. We discuss possible implications of this mating pattern for sexual selection on males. Key words: Euplectes orix, female choice, male quality, predation, random female settlement, sexual selection, weaverbirds. [Behav Ecol 11:378–386 (2000)] I n polygynous species with resource defense polygyny, territorial males provide resources that are important for reproduction such as food or nest sites within the territory to attract more than one female. Females often have to make a choice between a male without mate and an already mated male. If there is variation in the amount or quality of the resources provided by the males, it might pay for the female to choose an already mated male with, for example, a better territory, instead of an unmated male, because the advantage of higher territory quality outweighs the disadvantage of sharing the territory and the available food within the territory with another female. If the quality differences among territories are large, this will lead to high variation in male mating success (polygyny threshold model; Verner and Willson, 1966; Orians, 1969), and female mating preferences can be explained by direct benefits (e.g., better offspring survival resulting from higher food resources within the territory). In contrast, in polygynous species, where males provide females with little material resources, such direct benefits of female mate choice are less likely to fully explain female mating preferences. Instead, indirect mechanisms as proposed by ‘‘good genes’’ models of sexual selection may play a more important role. We studied sexual selection in the red bishop (Euplectes orix), a sexually dimorphic and polygynous weaverbird from Southern Africa. Males in breeding plumage establish and defend territories in reedbeds or bullrush stands around water, where they construct several nests during a breeding season to which they try to attract females. Most territories contain one or more empty nests at any time during the breeding