Phillips Jessica Ann, Fayet Annette L, Guilford Tim, Manco Fabrizio, Warwick-Evans Victoria, Trathan Phil
Department of Zoology, Oxford University, 11a Mansfield Rd, Oxford, OX1 3SZ, UK.
Anglia Ruskin University, Cambridge Campus, East Rd, Cambridge, CB1 1PT, UK.
Mov Ecol. 2021 May 4;9(1):22. doi: 10.1186/s40462-021-00261-x.
According to central place foraging theory, animals will only increase the distance of their foraging trips if more distant prey patches offer better foraging opportunities. Thus, theory predicts that breeding seabirds in large colonies could create a zone of food depletion around the colony, known as "Ashmole's halo". However, seabirds' decisions to forage at a particular distance are likely also complicated by their breeding stage. After chicks hatch, parents must return frequently to feed their offspring, so may be less likely to visit distant foraging patches, even if their quality is higher. However, the interaction between prey availability, intra-specific competition, and breeding stage on the foraging decisions of seabirds is not well understood. The aim of this study was to address this question in chinstrap penguins Pygoscelis antarcticus breeding at a large colony. In particular, we aimed to investigate how breeding stage affects foraging strategy; whether birds foraging far from the colony visit higher quality patches than available locally; and whether there is evidence for intraspecific competition, indicated by prey depletions near the colony increasing over time, and longer foraging trips.
We used GPS and temperature-depth recorders to track the foraging movements of 221 chinstrap penguins from 4 sites at the South Orkney Islands during incubation and brood. We identified foraging dives and calculated the index of patch quality based on time allocation during the dive to assess the quality of the foraging patch.
We found that chinstrap penguin foraging distance varied between stages, and that trips became shorter as incubation progressed. Although patch quality was lower near the colony than at more distant foraging patches, patch quality near the colony improved over the breeding season.
These results suggest chinstrap penguin foraging strategies are influenced by both breeding stage and prey distribution, and the low patch quality near the colony may be due to a combination of depletion by intraspecific competition but compensated by natural variation in prey. Reduced trip durations towards the end of the incubation period may be due to an increase in food availability, as seabirds time their reproduction so that the period of maximum energy demand in late chick-rearing coincides with maximum resource availability in the environment. This may also explain why patch quality around the colony improved over the breeding season. Overall, our study sheds light on drivers of foraging decisions in colonial seabirds, an important question in foraging ecology.
根据中心地觅食理论，只有当更远距离的猎物斑块提供更好的觅食机会时，动物才会增加其觅食行程的距离。因此，该理论预测，在大群体中繁殖的海鸟可能会在群体周围形成一个食物耗尽区，即“阿什莫尔光环”。然而，海鸟在特定距离觅食的决定可能也会因其繁殖阶段而变得复杂。雏鸟孵化后，父母必须频繁返回喂养后代，因此即使远处觅食斑块的质量更高，它们也可能不太可能前往。然而，猎物可获得性、种内竞争和繁殖阶段对海鸟觅食决定的相互作用尚未得到充分理解。本研究的目的是在一个大群体中繁殖的南极帽带企鹅身上解决这个问题。具体而言，我们旨在研究繁殖阶段如何影响觅食策略；远离群体觅食的鸟类是否会前往比当地可获得的更高质量的斑块；以及是否有证据表明存在种内竞争，表现为群体附近的猎物消耗随时间增加以及觅食行程变长。
我们使用全球定位系统（GPS）和温度深度记录仪，在孵化期和育雏期跟踪了南奥克尼群岛4个地点的221只南极帽带企鹅的觅食活动。我们识别出觅食潜水，并根据潜水期间的时间分配计算斑块质量指数，以评估觅食斑块的质量。
我们发现南极帽带企鹅的觅食距离在不同阶段有所变化，并且随着孵化进程的推进，行程变短。尽管群体附近的斑块质量低于更远距离的觅食斑块，但群体附近的斑块质量在繁殖季节有所改善。
这些结果表明，南极帽带企鹅的觅食策略受到繁殖阶段和猎物分布的影响，群体附近较低的斑块质量可能是种内竞争消耗的结果，但也受到猎物自然变化的补偿。孵化期接近尾声时行程持续时间缩短可能是由于食物可获得性增加，因为海鸟会调整它们的繁殖时间，使得雏鸟后期最大能量需求期与环境中最大资源可获得期相吻合。这也可能解释了为什么群体周围的斑块质量在繁殖季节有所改善。总体而言，我们的研究揭示了群居海鸟觅食决定的驱动因素，这是觅食生态学中的一个重要问题。
