The effects of experimentally elevated testosterone and food deprivation on food consumption and prey size preferences in male dark-eyed juncos (Junco hyemalis, Emberizidae : Passeriformes)

Numerous studies have shown that the experimental elevation of circulating levels of testosterone reduces parental behaviour in male birds, particular ly the provisioning of young. The mechanisms responsible for this change in behaviour are not fully understood. In this study, we examine the effects of elevated testosterone on food consumption and prey selection, both of wh ich have potential consequences for nestling provisioning behaviour. We man ipulated testosterone and performed two experiments on a captive, non-breed ing population of male dark-eyed juncos (Junco hyemalis) on long day-length s. In the first experiment, we subjected juncos to 3 h of food deprivation and compared food consumption and prey size selection by males with elevate d testosterone (testosterone males) to that of control males. Testosterone males consumed more food than control males and showed a preference for lar ger prey. In a second experiment in which small prey were more abundant tha n large prey, food consumption and prey size preferences did not differ bet ween testosterone and control males. We also manipulated the duration of fo od deprivation in the second experiment. Males of both treatments consumed more small prey under conditions of mild (1 h) or moderate (5 h) food depri vation and consumed more large prey under conditions of intermediate (3 h) food deprivation. We discuss our results and the effects that testosterone has on self-maintenance behaviour and male parental effort.