Biology Department, Dalhousie University, Halifax, NS Canada.
Fish Ecology & Conservation Physiology Lab, Carleton University, Ottawa, ON Canada.
Mov Ecol. 2014 Nov 19;2(1):23. doi: 10.1186/s40462-014-0023-4. eCollection 2014.
Animals adjust activity budgets as competing demands for limited time and energy shift across life history phases. For far-ranging migrants and especially pelagic seabirds, activity during breeding and migration are generally well studied but the "overwinter" phase of non-breeding has received less attention. Yet this is a critical time for recovery from breeding, plumage replacement and gaining energy stores for return migration and the next breeding attempt. We aimed to identify patterns in daily activity budgets (i.e. time in flight, floating on the water's surface and active foraging) and associated spatial distributions during overwinter for the laysan Phoebastria immutabilis and black-footed P. nigripes albatrosses using state-space models and generalized additive mixed-effects models (GAMMs). We applied these models to time-series of positional and immersion-state data from small light- and conductivity-based data loggers.
During overwinter, both species exhibited a consistent 'quasi-flightless' stage beginning c. 30 days after initiating migration and lasting c. 40 days, characterized by frequent long bouts of floating, very little sustained flight, and infrequent active foraging. Minimal daily movements were made within localized areas during this time; individual laysan albatross concentrated into the northwest corner of the Pacific while black-footed albatross spread widely across the North Pacific Ocean basin. Activity gradually shifted toward increased time in flight and active foraging, less time floating, and greater daily travel distances until colony return c. 155 days after initial departure.
Our results demonstrate that these species make parallel adjustments to activity budgets at a daily time-scale within the overwinter phase of non-breeding despite different at-sea distributions and phenologies. The 'quasi-flightless' stage likely reflects compromised flight from active wing moult while the subsequent increase in activity may occur as priorities shift toward mass gain for breeding. The novel application of a GAMM-based approach used in this study offers the possibility of identifying population-level patterns in shifting activity budgets over extended periods while allowing for individual-level variation in the timing of events. The information gained can also help to elucidate the whereabouts of areas important at different times across life history phases for far-ranging migrants.
随着有限时间和精力在生命史阶段之间的竞争需求发生变化，动物会调整活动预算。对于远程迁徙的动物，特别是远洋海鸟，繁殖期和迁徙期的活动通常得到了很好的研究，但繁殖期以外的“越冬”阶段则受到较少关注。然而，这是繁殖、换羽和为返回迁徙和下一次繁殖尝试积累能量储备的关键时期。我们的目的是利用状态空间模型和广义加性混合效应模型（GAMMs）来确定夏威夷凤头燕鸥（Phoebastria immutabilis）和黑脚信天翁（P. nigripes）越冬期间的日常活动预算（即飞行、漂浮在水面上和主动觅食的时间）和相关的空间分布模式。我们将这些模型应用于小型光和电导率数据记录器的位置和浸入状态时间序列数据。
在越冬期间，两种物种都表现出一致的“准飞行”阶段，从开始迁徙后约 30 天开始，持续约 40 天，特征是频繁的长时间漂浮、很少持续的飞行和不频繁的主动觅食。在此期间，个体的每日移动距离很小，局限在局部区域内；夏威夷凤头燕鸥个体集中在太平洋的西北角，而黑脚信天翁则广泛分布在北太平洋。随着时间的推移，活动逐渐转向增加飞行和主动觅食的时间、减少漂浮的时间以及增加每日旅行距离，直到离巢约 155 天后返回繁殖地。
我们的研究结果表明，尽管在海洋中的分布和物候期不同，这两种物种在繁殖期以外的越冬阶段都以每日时间尺度调整活动预算。“准飞行”阶段可能反映了主动换羽时飞行能力的下降，而随后活动的增加可能是由于繁殖期体重增加的优先级提高所致。本研究中应用的基于 GAMM 的方法的新颖应用提供了在较长时间内识别活动预算变化的种群水平模式的可能性，同时允许事件时间的个体水平变化。获得的信息还可以帮助阐明对于远程迁徙动物来说，在不同生命史阶段的不同时间，哪些区域是重要的。
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