Wildlife Biology Program, University of Montana, Missoula, MT, USA.
Horm Behav. 2010 Jul;58(2):297-305. doi: 10.1016/j.yhbeh.2010.03.002. Epub 2010 Mar 15.
Fledging is a major life transition for birds, when juveniles move from the safety of a nest into an environment where they must find food and avoid predators. The timing of fledging within a season can have significant effects on future survival and breeding success. Proximate triggers of fledging are unknown: though wing development is likely a primary factor, other physiological changes, such as elevated plasma corticosterone (CORT), may affect fledging behavior. Laysan Albatross (Phoebastria immutabilis) chicks have an extended post-hatching period during which they reach 150% of adult mass. However, approaching fledging, chicks fast for days to weeks and lose mass while still putting energy into feather growth. We evaluated chick morphology and physiology to elucidate proximate triggers of fledging. As in some other species, CORT increased as chicks fasted and lost body mass. At the same time, corticosteroid binding globulin (CBG) declined, thus amplifying free CORT prior to fledging. Once chicks reached a morphological threshold, free CORT levels predicted how long they stayed at the colony: chicks with higher free CORT fledged sooner. To perturb the relationship between body condition, endocrine physiology, and fledging behavior, we supplementally fed chicks for the month before fledging. Fed birds had a slower decrease in body mass, slower decrease in CBG, slower increase in free CORT, and stayed at the colony longer after reaching a morphological threshold. Our study suggests that as chicks lose mass, free CORT acts as a signal of energetic or nutritional state to adjust the timing of fledging.
离巢是鸟类生命中的一个重要转折点，此时幼鸟离开巢穴，进入一个必须自己寻找食物并躲避捕食者的环境。在一个季节内离巢的时间会对未来的生存和繁殖成功产生重大影响。离巢的直接触发因素尚不清楚：尽管翅膀发育可能是一个主要因素，但其他生理变化，如血浆皮质酮（CORT）水平升高，可能会影响离巢行为。夏威夷嘲鸫（Laysan Albatross，Phoebastria immutabilis）雏鸟在孵化后有一个延长的后期阶段，在此期间它们会达到成年体重的 150%。然而，在接近离巢时，雏鸟会禁食数天到数周，体重减轻，同时仍在投入能量生长羽毛。我们评估了雏鸟的形态和生理状况，以阐明离巢的直接触发因素。与其他一些物种一样，随着雏鸟禁食和体重减轻，CORT 水平升高。与此同时，皮质类固醇结合球蛋白（CBG）下降，从而在离巢前放大游离 CORT。一旦雏鸟达到形态学阈值，游离 CORT 水平预测它们在群体中停留的时间：游离 CORT 水平较高的雏鸟离巢更早。为了干扰身体状况、内分泌生理学和离巢行为之间的关系，我们在离巢前一个月对雏鸟进行了补充喂养。喂养的鸟类体重下降速度较慢，CBG 下降速度较慢，游离 CORT 增加速度较慢，达到形态学阈值后在群体中停留的时间更长。我们的研究表明，随着雏鸟体重减轻，游离 CORT 作为能量或营养状态的信号，调节离巢的时间。
