1. Date and latitude interact to determine photoperiod, the daily period of daylight. This interaction has important implications for latitudinal migrants for whom daylight may be a resource or for whom photoperiod regulates annual transitions in life‐history stages (i.e. birds).
2. Using an established formula, we developed user‐interactive, animated models that enable the visualization of how latitude and date determine photoperiod for latitudinal migrants. We also calculated the photoperiodic schedules for a broad range of hypothetical migratory programmes and real migratory programmes newly available through the proliferation of citizen‐science data. This enabled us to infer the limitations some migratory programmes place on mechanisms for photoperiodic regulation of annual breeding.
3. In the vast majority of cases, the act of migrating elevates annual daylight exposure. This raises the hypothesis that daylight availability selects for latitudinal migration, potentially contributing to its evolution in animals such as diurnal birds with limited time during the spring and summer to feed young. However, photoperiodic mechanisms regulating annual cycles could constrain the evolution of such migrations, depending on how they affect photoperiodic schedules. Most migratory programmes are consistent with known mechanisms of avian photoperiodism, but the range of feasible mechanisms declines for transequatorial migrants, which experience semi‐annual, 180°‐phase‐shifts in their photoperiodic cycles.
4. Understanding photoperiodic constraints on migration is particularly important in this age of changing latitudinal distributions and phenologies driven by climate change.

中文翻译：

---

纬度对日光可用性的影响如何影响迁移和光周期的演变

1. 日期和纬度相互作用以确定光周期，即日间的白天。这种相互作用对以日光为资源或以光周期调节生活史阶段的年度过渡（即鸟类）的纬度迁徙者具有重要意义。
2. 通过使用既定公式，我们开发了用户交互的动画模型，可以可视化地确定纬度和日期如何确定纬度移民的光周期。我们还计算了通过公民科学数据的扩散而新获得的各种假设的移民计划和实际移民计划的光周期计划。这使我们能够推断出某些迁徙计划对光周期调节年度繁殖机制的限制。
3. 在大多数情况下，迁移行为会增加每年的日照量。这就提出了一个假设，即日光可利用性会选择纬度迁移，这可能会在春季和夏季以有限的时间喂养幼仔，从而促进其在诸如昼夜鸟类等动物中的进化。但是，调节周期的光周期机制可能会限制此类迁​​移的发展，具体取决于它们如何影响光周期计划。大多数迁徙程序与已知的鸟类光周期机制一致，但对于跨赤道移民来说，可行机制的范围会减少，这些移民在其光周期中经历了半年度180°相移。
4. 在这个由气候变化驱动的纬度分布和物候变化的时代，了解光周期对迁徙的制约尤为重要。