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Concentrations of gonadal steroids such as testosterone (T) often vary widely in natural populations, but the causes and particularly the consistency of this variation is relatively unexplored. In breeding males of a wild population of the dark-eyed junco (Junco hyemalis), we investigated seasonal and individual variation in circulating T during two(More)
To explore whether selection for testosterone-mediated traits in males might be constrained by costs of higher testosterone to females, we examined the effects of experimental elevation of plasma testosterone on physiological, reproductive, and behavioral parameters in a female songbird, the dark-eyed junco (Junco hyemalis). We used subcutaneous implants to(More)
1. Despite considerable recent interest in plasma and yolk testosterone (T) in female birds, relatively little is known about environmental regulation of female T, individual variation in female T or the relationship between plasma and yolk T. 2. In breeding females of a wild population of dark-eyed junco (Junco hyemalis), we assessed variation in the(More)
Understanding physiological and behavioral mechanisms underlying the diversity of observed life-history strategies is challenging because of difficulties in obtaining long-term measures of fitness and in relating fitness to these mechanisms. We evaluated effects of experimentally elevated testosterone on male fitness in a population of dark-eyed juncos(More)
Introduction Birds vary both inter-and intra-specifically in their phenotypes in ways that appear adaptive, and some of this variation is mediated by hormones. The challenge is to account for how and why such variation arises, both mechanistically and in terms of evolutionary forces. In this paper we outline some of the contributions to be expected from a(More)
Resource pulses can have cascading effects on the dynamics of multiple trophic levels. Acorn mast is a pulsed resource in oak-dominated forests that has significant direct effects on acorn predators and indirect effects on their predators, prey, and pathogens. We evaluated changes in acorn mast, rodent abundance, raptor abundance, and reproductive success(More)
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