Age and plumage related territory differences in male black redstarts: the (non)-adaptive significance of delayed plumage maturation

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Abstract
Yearling males of European black redstarts (Phoenicuros ochruros) in their first potential breeding season are strongly dichromatic exhibiting either a femalelike or a bright adult male-like plumage. In villages near Innsbruck, Austria we investigated age and plumage specific differences in territory acquisition, territory position relative to other males, territory character and quality, mating and reproductive success. Yearling black redstart males breed regularly and accounted for about 50% of territorial males. About 90% of all yearling males were found to be in the dull female-like plumage. However, our data do not support hypotheses which suggest that retaining a dull plumage during the first breeding season is adaptive. Territories of most female-like yearling males were established in suboptimal, often peripheral village zones with few neighbours, most of which were yearlings as well. In addition, regardless of time of arrival from wintering grounds these young males had lower mating success than adult males and male-like yearlings, lower brood success, and showed less ability to rear a second brood than adult males. In contrast, territories of male-like yearling males were situated significantly more often in village zones preferred by adult males and male-like yearling males settled more often near to adult males than did female-like yearling males. These results are inconsistent with predictions of breeding season communication hypotheses like the Female Mimicry Hypothesis or the Status Signaling Hypothesis, but are partly in agreement with the Reduced Investment Hypothesis. However, our observations do not support the basic assumption of this hypothesis that late spring arrival and the search for low cost territories represent an adaptive choice by yearling males. Dull yearling plumages in this species are therefore likely to be non-adaptive in the first breeding season, and might simply be the result of constraints on plumage development.