Research into plumage ornaments and plumage signals of individual state has focused primarily on males, while variation among females has received far less attention. White patches of plumage around the eye (eye patches) are a female-specific plumage trait in the wood duck, Aix sponsa, a sexually dimorphic species of cavity-nesting waterfowl in North America. We observed considerable variation in the size of these patches among females and sought to evaluate whether this trait might indicate individual quality (‘quality cost hypothesis’) or the influence of stress or past investment (‘stress indicator hypothesis’). We measured the area of female eye patches in five populations of wood ducks during three breeding seasons and examined whether eye patch area varied in relation to age, nest success, future breeding, activity and/or body condition. Eye patch area was highly variable among individuals but repeatable within individuals, varied across years and study sites, correlated strongly with age but weakly with an index of body condition. For individuals greater than 4 years of age, eye patch area was negatively related to the likelihood of returning to breed in the following year. Eye patch size was positively correlated with nest initiation date and this was more pronounced in older birds, but there was no correlation of eye patch area with clutch size or hatch success. Our results suggest that this unique female-specific plumage trait reflects individual age and future reproduction potential. Larger eye patches in older females may be an indicator of senescence or terminal investment, and we hypothesize that eye patch size could act as a signal of individual state or social status in this species.

中文翻译：

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雌性木鸭 Aix sponsa 的白色眼斑大小差异很大，可能反映个体状态或状况

对个体状态的羽毛装饰和羽毛信号的研究主要集中在雄性身上，而雌性之间的差异却很少受到关注。眼睛周围的白色羽毛斑块（眼斑块）是木鸭 Aix sponsa 中雌性特有的羽毛特征，这是北美的一种雌雄异体的窝巢水禽。我们观察到女性这些斑块的大小存在相当大的差异，并试图评估这种特征是否可能表明个体质量（“质量成本假设”）或压力或过去投资的影响（“压力指标假设”）。我们在三个繁殖季节测量了五个木鸭种群的雌性眼罩面积，并检查眼罩面积是否因年龄、筑巢成功率、未来繁殖、活动和/或身体状况而异。眼罩面积在个体之间变化很大，但在个体内可重复，随年份和研究地点而异，与年龄密切相关，但与身体状况指数相关性较弱。对于 4 岁以上的个体，眼罩面积与次年恢复繁殖的可能性呈负相关。眼罩大小与筑巢开始日期呈正相关，这在年长的鸟类中更为明显，但眼罩面积与窝大小或孵化成功率没有相关性。我们的研究结果表明，这种独特的女性特有的羽毛特征反映了个体年龄和未来的繁殖潜力。老年女性的大眼斑可能是衰老或最终投资的指标，