Avian incubation provides an opportunity to test how parental behavior and ecological conditions interact to shape variation in offspring traits along geographic gradients. In particular, the duration of the incubation period is shorter at higher latitudes, but the degree to which this pattern arises from genetic divergence in rates of growth and development versus from parentally‐mediated variation in egg temperatures is controversial. At higher latitudes parents have higher daytime incubation attentiveness, i.e. they spend a greater proportion of the day on the nest. However, interpreting latitudinal variation in behavior is complicated by latitudinal patterns in ambient temperature and day length. Here, we use 24‐h video recordings to compare the incubation behavior of orange‐crowned warblers Leiothlypis celata in California and Alaska and test how attentiveness varies between populations and as a function of temperature. Birds in Alaska had higher nest attentiveness during the day, despite experiencing similar ambient temperatures. However, when analyzed over 24‐h, the longer nighttime period in California almost entirely canceled out daytime attentiveness differences between populations, and differences in 24‐h attentiveness were small. Our work highlights how incorporating nighttime incubation behavior qualitatively alters latitudinal patterns of attentiveness, and how lower ambient temperatures cannot account for the higher attentiveness in a high latitude population. These populations differ in their incubation period lengths, and differentiating between evolved versus environmentally‐induced variation in offspring growth and development will help understand the fitness consequences of variation in developmental periods.

中文翻译：

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夜间长度对鸟类孵化注意力纬度变化的重要性

鸟类孵化提供了一个机会来测试亲代行为和生态条件如何相互作用以形成沿地理梯度的后代特征的变化。特别是，在高纬度地区，孵化期的持续时间较短，但这种模式是由生长和发育速度的遗传差异与亲本介导的鸡蛋温度变化引起的程度是有争议的。在高纬度地区，父母白天孵化的注意力更高，即他们一天中有更多的时间待在巢上。然而，由于环境温度和昼长的纬度模式，解释行为的纬度变化很复杂。这里，我们使用 24 小时的视频记录来比较加利福尼亚和阿拉斯加的橙冠莺 Leiothlypis celata 的孵化行为，并测试注意力如何在种群之间以及作为温度的函数而变化。尽管环境温度相似，但阿拉斯加的鸟类在白天的筑巢注意力更高。然而，当对 24 小时进行分析时，加利福尼亚较长的夜间时段几乎完全抵消了人群之间白天注意力的差异，并且 24 小时注意力的差异很小。我们的工作强调了纳入夜间孵化行为如何定性地改变注意力的纬度模式，以及较低的环境温度如何无法解释高纬度人群的较高注意力。这些种群的潜伏期长度不同，