Seasonal reproduction is a widespread adaptation in vertebrates, such that individuals time their reproductive efforts to match peak resource abundance. Individuals rely on environmental cues to regulate hormonal mechanisms governing timing of breeding. Historically, studies on physiological mechanisms of seasonal reproduction, specifically in birds, have disproportionately focused on males compared to females. For this review, I conducted a literature search of the last decade of avian research and found a persistent sex bias in the field of physiological mechanisms of seasonal reproduction. Using work conducted with the dark-eyed junco (Junco hyemalis) as a case study, I present a possible solution to combat the sex bias: natural comparisons of populations that differ in reproductive timing to investigate mechanisms of reproduction in both sexes. Populations of dark-eyed juncos that differ in migratory behavior (i.e., migrant and resident) exhibit overlapping ranges during winter and early spring; residents begin breeding in early spring prior to the departure of migrants. This system, and others like it, provides an opportunity to compare mechanisms of reproduction in populations that differ in reproductive timing despite experiencing the same environmental conditions in early spring. In juncos, migrant and resident females and males exhibit similar patterns of hypothalamic regulation of reproduction in early spring, but sex differences in gonadal sensitivity between the populations could be an important distinction that partially explains sex differences in reproductive development. Comparing mechanisms of reproduction in free-living populations and in captivity can reveal important mechanisms that determine the onset of reproductive development, as well as potential sex differences in these mechanisms. Understanding the mechanisms of reproductive phenology has important implications for understanding how species will survive and reproduce in a changing climate.

中文翻译：

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女性作为季节性繁殖的守门人：我们可以通过研究两性的生殖机制来了解什么

季节性繁殖是脊椎动物的一种普遍适应性，因此个体将繁殖努力的时间安排到与资源丰度相匹配的时间。个体依靠环境线索来调节控制繁殖时间的激素机制。从历史上看，对季节性繁殖的生理机制的研究，特别是在鸟类中，与雌性相比，雄性的研究重点不成比例。在这篇综述中，我对过去十年的鸟类研究进行了文献检索，发现季节性繁殖的生理机制领域存在持续的性别偏见。使用对黑眼 junco (Junco hyemalis) 进行的工作作为案例研究，我提出了一个可能的解决方案来对抗性别偏见：对生殖时间不同的种群进行自然比较，以研究两性的生殖机制。迁徙行为（即迁徙和常住）不同的黑眼鲎种群在冬季和早春期间表现出重叠的范围；居民在移民离开之前的早春开始繁殖。该系统和其他类似系统提供了一个机会，可以比较尽管早春环境条件相同，但繁殖时间不同的种群的繁殖机制。在 juncos 中，迁徙和居住的雌性和雄性在早春表现出相似的下丘脑生殖调节模式，但种群之间性腺敏感性的性别差异可能是一个重要的区别，部分解释了生殖发育中的性别差异。比较自由生活种群和圈养种群的生殖机制可以揭示决定生殖发育开始的重要机制，以及这些机制中潜在的性别差异。了解生殖物候的机制对于了解物种如何在不断变化的气候中生存和繁殖具有重要意义。