Sequential settlement by nesting male and female Baya weaverbirds Ploceus philippinus: the role of monsoon winds

Abstract

Theory predicts that females should track resources while making decisions about where to reproduce, and males should track females. However, when males create the resource that females require, female settlement follows that of males. In this situation, how do individuals make settling decisions and what are the fitness consequences of these decisions? Here, I test the hypothesis that environmental factors (wind direction and velocity) affect optimal nest placement and orientation, and thus male and female settlement, in Baya weaver Ploceus philippinus colonies. Nests experimentally placed in windward locations with entrance tubes oriented toward the wind were more likely to lose clutches of artificial eggs than were nests placed in other combinations of placement and orientation. Correspondingly, males built their nests strongly clustered on the leeward side of colony trees, with entrance tubes oriented away from the wind. However, females did not discriminate amongst natural nests on the basis of nest placement or orientation. This may be because the effect of wind on the success of natural nests was small and was overwhelmed by other causes of nest loss. I suggest that, in some situations, female preference may remain undetected because the options available to females are constrained by preceding settlement decisions by males. In these cases, it is necessary to manipulate male distribution outside the range of natural variation to gain a better understanding of selective pressures imposed by female preferences.