Brown David R, Sherry Thomas W
Department of Ecology and Evolutionary Biology, Tulane University, 310 Dinwiddie Hall, New Orleans, LA 70118, USA.
Oecologia. 2006 Aug;149(1):22-32. doi: 10.1007/s00442-006-0418-z. Epub 2006 Apr 26.
The hypothesis that migratory bird populations are limited during the non-breeding season is increasingly supported by empirical studies that also suggest consequences that carry-over into subsequent seasons. Although variation in food supply is the best supported explanation for non-breeding season limitation, the ecological mechanisms and physiological consequences are not well understood. We both supplemented and reduced Ovenbird (Seiurus aurocapilla) food availability on replicate plots in Jamaica in each of 3 years to determine the direct role of food in limiting the physical condition of Ovenbirds. Annual variation in rainfall and food supply created a natural experiment in parallel with manipulations. Sex and age-classes of Ovenbirds did not respond differently in terms of body condition to either food manipulation or natural variation in environmental conditions, suggesting that this population is not structured by strong dominance relationships. Ovenbird body mass, fat, and pectoralis muscle shape were positively and predictably related to manipulated food availability. Feather regrowth rate also responded positively to food supplementation and negatively to food reduction in the drier of 2 years. Prior to manipulation, annual variation in body mass corresponded to annual variation in food supply and rainfall, providing additional, correlational evidence of food limitation. Since multiple intercorrelated body condition indices of Ovenbirds responded directly to food supply, and since food supply influenced body condition independently of other habitat features, we argue that food is a primary driver of non-breeding season population limitation. Moreover, since these effects were observed during the late non-breeding period, when individuals are preparing to migrate, we infer that food availability likely initiates carry-over effects.
候鸟种群在非繁殖季节受到限制这一假说，越来越多地得到实证研究的支持，这些研究还表明其后果会延续到后续季节。尽管食物供应的变化是对非繁殖季节限制的最有力支持的解释，但生态机制和生理后果仍未得到很好的理解。我们在牙买加连续三年对重复地块上灶巢鸟（Seiurus aurocapilla）的食物可获得性进行了补充和减少，以确定食物在限制灶巢鸟身体状况方面的直接作用。降雨和食物供应的年度变化与人为操纵共同构成了一个自然实验。灶巢鸟的性别和年龄组在身体状况方面对食物操纵或环境条件的自然变化没有不同反应，这表明该种群没有由强烈的优势关系构成结构。灶巢鸟的体重、脂肪和胸肌形状与操纵的食物可获得性呈正相关且可预测。在两年中较干燥的一年，羽毛再生率对食物补充呈正反应，对食物减少呈负反应。在操纵之前，体重的年度变化与食物供应和降雨的年度变化相对应，提供了食物限制的额外相关证据。由于灶巢鸟多个相互关联的身体状况指标直接对食物供应做出反应，并且由于食物供应独立于其他栖息地特征影响身体状况，我们认为食物是限制非繁殖季节种群数量的主要驱动因素。此外，由于这些影响是在非繁殖后期观察到的，此时个体正准备迁徙，我们推断食物可获得性可能引发了延续效应。
