Jarrett Crinan, Powell Luke L, Claire Tabe T Regine, Tchoumbou Melanie, Helm Barbara
Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, G12 8QQ UK.
Biodiversity Initiative, Houghton, MI 49913 USA.
J Ornithol. 2021;162(3):645-653. doi: 10.1007/s10336-021-01859-z. Epub 2021 Feb 15.
Wood Warblers, an Afro-Palearctic migrant species, are declining steadily in Europe likely due to mortality outside their breeding grounds. However, little is known about their overwintering, and records about the sensitive life-cycle stage of moult in Africa are practically absent. To fill this gap, we report on moult of Wood Warblers captured over two winters (January-February) in 2019-2020 in Cameroon. We caught 14 individuals, of which 12 were monitored for flight feather moult. All inspected individuals showed advanced stages of flight feather renewal. Despite low sample sizes, Underhill-Zucchini moult models aptly explained variation in primary and secondary moult ( = 0.61). Estimated moult onset date was 26 December, completion date was 25 February, and moult duration was 61 days. These findings fit well with experimental data on the annual cycle and the timing of recently published migration tracks of Wood Warblers. Jointly, the data suggest that moult timing is set by an internal programme, which enables Wood Warblers to organise their multi-stage migration such that they reach suitable moulting habitat in time, and can depart in time with a fresh plumage for the breeding grounds. In our study, moult occurred during the peak of the dry season, which in Cameroon nonetheless shows high relative humidity. During our mist-netting on 28 cocoa plantations of varying shade cover, Wood Warblers were caught on 6 farms whose canopies were comparatively open. These data suggest that the birds encounter in Cameroon relatively stable climatic conditions for moult, and do not measurably prefer closed-canopy forests. Our findings are important, because successful moult increases survival prospects and because moult needs to be safely embedded in a migratory life cycle. Hence, information on moult timing and location is essential for identifying year-round vulnerabilities of Wood Warblers.
林莺是一种在非洲-古北界迁徙的鸟类，在欧洲数量正稳步下降，这可能是由于其在繁殖地以外的死亡率所致。然而，人们对它们的越冬情况知之甚少，关于它们在非洲换羽这一敏感生命周期阶段的记录实际上也没有。为填补这一空白，我们报告了2019年至2020年在喀麦隆两个冬季（1月至2月）捕获的林莺的换羽情况。我们捕获了14只个体，其中12只被监测飞羽的换羽情况。所有检查的个体都显示出飞羽更新的后期阶段。尽管样本量较小，但Underhill-Zucchini换羽模型恰当地解释了初级飞羽和次级飞羽换羽的变化（R² = 0.61）。估计换羽开始日期为12月26日，完成日期为2月25日，换羽持续时间为61天。这些发现与关于林莺年度周期和最近公布的迁徙路线时间的实验数据非常吻合。综合来看，这些数据表明换羽时间是由一个内部程序设定的，这使得林莺能够安排它们的多阶段迁徙，以便及时到达合适的换羽栖息地，并能及时带着新羽毛出发前往繁殖地。在我们的研究中，换羽发生在旱季的高峰期，不过喀麦隆的旱季相对湿度仍然较高。在我们对28个不同遮荫程度的可可种植园进行雾网捕鸟期间，在6个树冠相对开阔的农场捕获到了林莺。这些数据表明，这些鸟类在喀麦隆遇到了相对稳定的换羽气候条件，并且并没有明显偏好树冠封闭的森林。我们的发现很重要，因为成功换羽会增加生存前景，而且换羽需要安全地融入迁徙生命周期。因此，关于换羽时间和地点的信息对于确定林莺全年的脆弱性至关重要。
