Frankish Caitlin K, Manica Andrea, Phillips Richard A
1British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET UK.
2Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ UK.
Mov Ecol. 2020 Feb 7;8:7. doi: 10.1186/s40462-020-0194-0. eCollection 2020.
Foraging performance is widely hypothesized to play a key role in shaping age-specific demographic rates in wild populations, yet the underlying behavioral changes are poorly understood. Seabirds are among the longest-lived vertebrates, and demonstrate extensive age-related variation in survival, breeding frequency and success. The breeding season is a particularly critical phase during the annual cycle, but it remains unclear whether differences in experience or physiological condition related to age interact with the changing degree of the central-place constraint in shaping foraging patterns in time and space.
Here we analyze tracking data collected over two decades from congeneric black-browed (BBA) and grey-headed (GHA) albatrosses, and , breeding at South Georgia. We compare the foraging trip parameters, at-sea activity (flights and landings) and habitat preferences of individuals aged 10-45 years and contrast these patterns between the incubation and early chick-rearing stages.
Young breeders of both species showed improvements in foraging competency with age, reducing foraging trip duration until age 26. Thereafter, there were signs of foraging senescence; older adults took gradually longer trips, narrowed their habitat preference (foraging within a smaller range of sea surface temperatures) (GHA), made fewer landings and rested on the water for longer (BBA). Some age-specific effects were apparent for each species only in certain breeding stages, highlighting the complex interaction between intrinsic drivers in determining individual foraging strategies.
Using cross-sectional data, this study highlighted clear age-related patterns in foraging behavior at the population-level for two species of albatrosses. These trends are likely to have important consequences for the population dynamics of these threatened seabirds, as young or old individuals may be more vulnerable to worsening environmental conditions.
觅食表现被广泛认为在塑造野生种群特定年龄的人口统计学率方面起着关键作用，但其潜在的行为变化却知之甚少。海鸟是寿命最长的脊椎动物之一，在生存、繁殖频率和成功率方面表现出与年龄相关的广泛差异。繁殖季节是年度周期中特别关键的阶段，但尚不清楚与年龄相关的经验或生理状况差异是否与中心地限制程度的变化相互作用，从而在时空上塑造觅食模式。
在此，我们分析了二十多年来从在南乔治亚岛繁殖的同属黑眉信天翁（BBA）和灰头信天翁（GHA）收集的追踪数据。我们比较了10至45岁个体的觅食行程参数、海上活动（飞行和着陆）以及栖息地偏好，并对比了孵化期和雏鸟早期育雏阶段的这些模式。
两种信天翁的年轻繁殖者的觅食能力都随着年龄的增长而提高，在26岁之前觅食行程持续时间逐渐缩短。此后，出现了觅食衰老的迹象；年龄较大的成年信天翁的行程逐渐变长，栖息地偏好范围变窄（在较窄的海面温度范围内觅食）（灰头信天翁），着陆次数减少，在水面休息的时间更长（黑眉信天翁）。某些特定年龄效应仅在某些繁殖阶段对每个物种明显，这突出了内在驱动因素在决定个体觅食策略方面的复杂相互作用。
本研究利用横断面数据，突出了两种信天翁在种群水平上觅食行为中与年龄相关的明显模式。这些趋势可能对这些受威胁海鸟的种群动态产生重要影响，因为年轻或年老个体可能更容易受到环境条件恶化的影响。
