Foraging in a dynamic environment: response of four sympatric sub-Antarctic albatross species to interannual environmental variability

Seasonal and annual climate variations are linked to fluctuations in the abundance and distribution of resources, posing a significant challenge to animals that need to adjust their foraging behaviour accordingly. Particularly during adverse conditions, and while energetically constrained when breeding, animals ideally need to be flexible in their foraging behaviour. Such behavioural plasticity may separate 'winners' from 'losers' in light of rapid environmental changes due to climate change. Here, the foraging behaviour of four sub-Antarctic albatross species was investigated from 2015/16 to 2017/18, a period characterized by pronounced environmental variability. Over three breeding seasons on Marion Island, Prince Edward Archipelago, incubating wandering (WA, Diomedea exulans; n=45), grey-headed (GHA, Thalassarche chrysostoma; n=26), sooty (SA, Phoebetria fusca; n=23) and light-mantled (LMSA, P. palpebrata; n=22) albatrosses were tracked with GPS loggers. The response of birds to environmental variability was investigated by quantifying inter-annual changes in their foraging behaviour along two axes: spatial distribution, using kernel density analysis, and foraging habitat preference, using generalized additive mixed models and Bayesian mixed models. All four species were shown to respond behaviourally to environmental variability, but with substantial differences in their foraging strategies. WA was most general in its habitat use defined by sea surface height, eddy kinetic energy, wind speed, ocean floor slope and sea level anomaly, with individuals foraging in a range of habitats. In contrast, the three smaller albatrosses exploited two main foraging habitats, with habitat use varying between years. Generalist habitat use by WA and inter-annually variable use of habitats by GHA, SA and LMSA would likely offer these species some resilience to predicted changes in climate such as warming seas and strengthening of westerly winds. However, future investigations need to consider other life history stages coupled with demographic studies, to better understand the link between behavioural plasticity and population responses.

季节与年际气候波动与资源丰度及分布的变化紧密相关，这对需要据此调整觅食行为的动物而言构成了严峻挑战。尤其是在不利环境条件下，以及繁殖期间面临能量约束时，动物亟需在觅食行为上具备灵活性。鉴于气候变化引发的快速环境变化，这种行为可塑性或将成为区分“优胜者”与“失败者”的关键。
本研究于2015/16至2017/18年间对四种亚南极信天翁的觅食行为展开调查，该时段环境波动特征显著。
研究在爱德华王子群岛马里恩岛的三个繁殖季内开展，通过GPS记录仪（GPS logger）追踪了正在孵卵的四种信天翁：漂泊信天翁（wandering albatross, WA, *Diomedea exulans*; n=45）、灰头信天翁（grey-headed albatross, GHA, *Thalassarche chrysostoma*; n=26）、乌信天翁（sooty albatross, SA, *Phoebetria fusca*; n=23）以及浅背信天翁（light-mantled albatross, LMSA, *P. palpebrata*; n=22）。
本研究通过两个维度量化鸟类觅食行为的年际变化，以此探究其对环境波动的响应：一是空间分布特征（核密度分析，kernel density analysis），二是觅食生境偏好（广义加性混合模型，generalized additive mixed models；贝叶斯混合模型，Bayesian mixed models）。研究表明，四种信天翁均会在行为上响应环境波动，但其觅食策略存在显著差异。
漂泊信天翁的生境利用最为泛化，其生境选择由海面高度、涡动动能、风速、海底坡度与海平面异常所决定，个体可在多种生境中觅食。相较而言，其余三种体型较小的信天翁仅利用两类主要觅食生境，且其生境利用模式存在年际差异。
漂泊信天翁的泛化生境利用策略，以及灰头信天翁、乌信天翁与浅背信天翁的年际可变生境利用模式，或可帮助这些物种应对预期的气候变化——包括海洋升温与西风增强。不过，未来的研究需结合种群人口统计学调查，覆盖其他生活史阶段，方能更深入地解析行为可塑性与种群响应之间的关联。