Emmerson Louise, Walsh Sarina, Southwell Colin
Australian Antarctic Division Department of Environment and Energy Kingston Tasmania Australia.
Melbourne Aquarium Melbourne Victoria Australia.
Ecol Evol. 2019 Mar 29;9(8):4637-4650. doi: 10.1002/ece3.5067. eCollection 2019 Apr.
The difficulty in studying nonbreeding birds means that little is known about them or their resource requirements, despite forming a large and significant component of a population. One way to assess food requirements is to examine changes in body mass, because it indicates the amount of food acquired. In terms of body mass changes, our expectation is that nonbreeders will either (a) be in poorer condition than the breeders which potentially explains why they do not breed or (b) remain at a stable higher mass as they are unconstrained by the physiological costs associated with rearing chicks. Here, we interrogate body mass datasets of breeding and nonbreeding birds of two penguin species to assess these predictions and determine whether differences in mass exist between these two groups throughout the breeding season. The first dataset is from a wild Adélie penguin population, where bird mass was recorded automatically and breeding status determined from a resighting program. A second population of captive gentoo penguins were weighed regularly each breeding season. We demonstrate that although there were times in each year when breeders were heavier than their nonbreeding counterparts for both populations, the mass changes showed qualitatively similar patterns throughout the breeding season irrespective of breeding status. Heavier breeders at times during the breeding season are not unexpected but the overall similar pattern of mass change irrespective of breeding status is in contrast to expectations. It appears that breeding status per se and the constraints that breeding places on birds are not the only driver of changes in mass throughout the breeding season and, although not explicitly studied here, the role of hormones in driving changes in appetite could be key to explain these results. These results present a significant step toward understanding food requirements of nonbreeders in avian populations.
研究非繁殖期鸟类存在困难，这意味着尽管它们在种群中占很大且重要的比例，但我们对它们及其资源需求却知之甚少。评估食物需求的一种方法是检查体重变化，因为体重变化能表明获取的食物量。就体重变化而言，我们预期非繁殖期鸟类要么（a）身体状况比繁殖期鸟类差，这可能解释了它们不繁殖的原因；要么（b）由于不受育雏相关生理成本的限制，体重保持在稳定的较高水平。在此，我们分析了两种企鹅繁殖期和非繁殖期鸟类的体重数据集，以评估这些预测，并确定在整个繁殖季节这两组鸟类的体重是否存在差异。第一个数据集来自野生阿德利企鹅种群，在那里自动记录鸟类体重，并通过重新观察计划确定繁殖状态。第二个圈养巴布亚企鹅种群在每个繁殖季节定期称重。我们证明，尽管每年都有一段时间，这两个种群中繁殖期鸟类的体重都比非繁殖期鸟类重，但无论繁殖状态如何，整个繁殖季节体重变化的模式在质量上是相似的。繁殖期某些时候繁殖期鸟类体重较重并不意外，但无论繁殖状态如何，体重变化的总体模式相似，这与预期相反。看来繁殖状态本身以及繁殖对鸟类的限制并非整个繁殖季节体重变化的唯一驱动因素，尽管此处未明确研究，但激素在驱动食欲变化方面的作用可能是解释这些结果的关键。这些结果朝着理解鸟类种群中非繁殖期鸟类的食物需求迈出了重要一步。
