Data from: Variation in growth drives the duration of parental care: a test of Ydenberg's model

The duration of parental care in animals varies widely, from none to lifelong. Such variation is typically thought to represent a trade-off between growth and safety. Seabirds show wide variation in the age at which offspring leave the nest, making them ideal to test the idea that a trade-off between high energy gain at sea and high safety at the nest drives variation in departure age (Ydenberg’s model). To directly test the model assumptions, we attached time-depth recorders to murre parents (fathers [which do all parental care at sea] and mothers; of each). Except for the initial mortality experienced by chicks departing from the colony, the mortality rate at sea was similar to the mortality rate at the colony. However, energy gained by the chick per day was ∼2.1 times as high at sea compared with at the colony because the father spent more time foraging, since he no longer needed to spend time commuting to and from the colony. Compared with the mother, the father spent ∼2.6 times as much time diving per day and dived in lower-quality foraging patches. We provide a simple model for optimal departure date based on only (1) the difference in growth rate at sea relative to the colony and (2) the assumption that transition mortality from one life-history stage to the other is size dependent. Apparently, large variation in the duration of parental care can arise simply as a result of variation in energy gain without any trade-off with safety.

动物的亲本抚育时长差异悬殊，从完全缺乏抚育到终身抚育不等。此类差异通常被认为体现了生长与安全之间的权衡关系。海鸟在雏鸟离巢年龄上存在广泛差异，使其成为检验"海上高能量获取与巢内高安全性之间的权衡驱动离巢年龄差异（伊登伯格模型（Ydenberg’s model））"这一假说的理想研究对象。为直接检验该模型的假设前提，我们为海鸠（murre）的亲本个体，即每对亲本中的父本与母本——其中父本负责全程海上抚育——佩戴了时间深度记录仪（time-depth recorder）。除雏鸟离群时遭遇的初始死亡率外，雏鸟在海上的死亡率与巢内死亡率基本持平。然而，雏鸟每日获取的能量约为巢内环境的2.1倍，这是因为父本无需再往返巢群，因而能够投入更多时间觅食。与母本相比，父本每日的潜水时长约为后者的2.6倍，且其潜水觅食的生境斑块质量更低。我们构建了一个仅基于两项条件的最优离巢日期简易模型：其一为海上相较于巢内的生长速率差异，其二为不同生活史阶段间的转换死亡率取决于个体体型这一假设。研究表明，亲本抚育时长的巨大差异，完全可仅由能量获取的差异所导致，而无需涉及与安全性的权衡。