Corticosterone affects physiology and behavior both during normal daily processes but also in response to environmental challenges and is known to mediate life history trade-offs. Many studies have investigated patterns of corticosterone production at targeted times of year, while ignoring underlying annual profiles. We aimed to understand the annual regulation of hypothalamic-pituitary-adrenal (HPA) axis function of both migrant (Zonotrichia leucophrys gambelii; n = 926) and resident (Z. l. nutalli; n = 688) subspecies of white-crowned sparrow and how it is influenced by environmental conditions – wind, precipitation, and temperature. We predicted that more dramatic seasonal changes in baseline and stress-induced corticosterone would occur in migrants to precisely time the onset of breeding and cope with environmental extremes on their arctic breeding grounds, while changes in residents would be muted as they experience a more forgiving breeding schedule and comparatively benign environmental conditions in coastal California. During the course of a year, the harshest conditions were experienced the summer breeding grounds for migrants, at which point they had higher corticosterone levels compared to residents. For residents, the winter months coincided with harshest conditions at which point they had higher corticosterone levels than migrants. For both subspecies, corticosterone tended to rise as environmental conditions became colder and windier. We found that the annual maxima in stress-induced corticosterone occurred prior to egg lay for all birds except resident females. Migrants had much higher baseline and acute stress-induced corticosterone during breeding compared to residents; where in a harsher environment the timing of the onset of reproduction is more critical because the breeding season is shorter. Interestingly, molt was the only stage within the annual cycle in which subspecies differences were absent suggesting that a requisite reduction in corticosterone may have to be met for feather growth. These data suggest that modulation of the HPA axis is largely driven by environmental factors, social cues, and their potential interactions with a genetic program.

皮质酮不仅在正常的日常过程中影响生理和行为，而且在应对环境挑战时也会影响生理和行为，众所周知，它可以介导生命史的取舍。许多研究调查了每年目标时间的皮质酮生产模式，而忽略了潜在的年度概况。我们的目的是了解下丘脑-垂体-肾上腺（HPA）的年调节两个外出的轴功能（Zonotrichia leucophrys gambelii ; N = 926）和驻留（Z.。升nutalli; n = 688）白冠麻雀的亚种，以及它如何受到风，降水和温度等环境条件的影响。我们预测，移民中基线和压力诱发的皮质酮的季节性变化将更为剧烈，以准确计时繁殖的开始时间并应对北极繁殖场上的极端环境，而居民的变化将被忽略，因为他们经历了更加宽容的繁殖日程安排和加利福尼亚沿海地区相对良好的环境条件。在一年的时间里，最艰苦的条件是夏季移民的繁殖地，此时，与居民相比，他们的皮质酮水平更高。对于居民来说 冬季恰逢最恶劣的条件，那时他们的皮质酮水平高于移徙者。对于这两个亚种，随着环境条件变得更冷和更风，皮质酮趋于上升。我们发现，除常驻雌性外，所有鸟类在产卵前的应激诱导的皮质类固醇的年度最大值发生。与居民相比，移民在繁殖过程中具有更高的基线和急性应激诱导的皮质酮。在较恶劣的环境中，繁殖的时间越短，繁殖开始的时间就越关键。有趣的是，蜕皮是一年周期中唯一没有亚种差异的阶段，这表明为羽毛生长可能必须满足降低皮质酮的需要。