Biology, University of Washington, Seattle, WA, United States of America.
Center for Ecosystem Sentinels, Seattle, WA, United States of America.
PeerJ. 2024 Oct 21;12:e17937. doi: 10.7717/peerj.17937. eCollection 2024.
The proportions of individuals in various age classes in a population of wild animals affect population trends, behaviors, learning, and social structures. Knowledge of age structure is needed for effective conservation and management of populations. However, it is not always possible to determine the age or age class of individual animals, and hence the age structure of the population. Penguins, like most birds, cannot be aged once they molt into adult plumage. penguins attain adult plumage at 6 to 24 months of age, and individuals can live more than 30 years. We studied foot darkening in the four species of penguins to determine if age class can be determined from foot color. We compared how foot color changes with age among the four species to investigate potential functions of the darkening. We found that penguins have pale feet at hatching and the feet become darker with age throughout the lives of individuals. We showed that we can accurately predict the age structure of a colony of Magellanic penguins , but not the ages of individual penguins, based on a sample of foot colors. The timing of foot darkening within species was consistent with foot color functioning in protection from UV radiation, and not with foot color functioning in thermoregulation. The species that breeds at the lowest latitudes and experiences the highest UV radiation (Galápagos penguins ) had feet that darkened at the earliest ages, and the species that breed at higher latitudes and experience less intense insolation (African and Magellanic penguins) had feet that darkened latest. Humboldt penguins breed mostly at low latitudes and foot darkening was intermediate between Galápagos and Magellanic penguins. We also found that males' feet darken somewhat earlier than females' feet, likely because females spend more time in their nests (burrows or under vegetation) than males and have less sun exposure. We found that feet darkened in an individual over years, but not within a breeding season. The color change is a life-long process, likely an evolutionary adaptation within species, not a seasonal, temporary response to UV radiation. We propose foot darkening as a way to assess age structure in penguins. Foot color in a colony of Magellanic penguins can provide a rapid, noninvasive method to estimate the age structure of the colony.
野生动物种群中不同年龄阶段个体的比例会影响种群趋势、行为、学习和社会结构。了解年龄结构对于有效保护和管理种群至关重要。然而，确定个体动物的年龄或年龄组并非总是可行的，因此无法确定种群的年龄结构。企鹅与大多数鸟类一样，一旦进入成年羽毛期就无法确定年龄。企鹅在 6 到 24 个月时达到成年羽毛期，并且个体可以活 30 多年。我们研究了四种企鹅的足部黑化，以确定是否可以从足部颜色确定年龄组。我们比较了四种企鹅中足部颜色随年龄的变化，以研究黑化的潜在功能。我们发现，小企鹅孵化时足部呈浅色，随着个体年龄的增长，足部颜色逐渐变深。我们表明，我们可以根据足部颜色样本准确预测麦哲伦企鹅的殖民地的年龄结构，但不能预测个体企鹅的年龄。在同一物种内，足部黑化的时间与足部颜色在保护紫外线辐射方面的功能一致，而与足部颜色在体温调节方面的功能不一致。繁殖地纬度最低、紫外线辐射最强的物种（加拉帕戈斯企鹅）足部黑化的年龄最早，繁殖地纬度较高、光照强度较弱的物种（非洲企鹅和麦哲伦企鹅）足部黑化的年龄最晚。洪堡企鹅主要在低纬度繁殖，其足部黑化程度介于加拉帕戈斯企鹅和麦哲伦企鹅之间。我们还发现，雄性的足部黑化时间比雌性略早，可能是因为雌性在巢（洞穴或植被下）中停留的时间比雄性长，暴露在阳光下的时间更少。我们发现，个体的足部在几年内逐渐变黑，但在一个繁殖季节内不会。颜色变化是一个终身过程，可能是物种内的一种进化适应，而不是对紫外线辐射的季节性、临时反应。我们提出足部黑化是评估企鹅年龄结构的一种方法。麦哲伦企鹅群的足部颜色可以提供一种快速、非侵入性的方法来估计群体的年龄结构。
