Howard Jennifer L, Tompkins Emily M, Anderson David J
Department of Biology Wake Forest University Winston-Salem NC USA.
Ecol Evol. 2021 Mar 10;11(9):4084-4100. doi: 10.1002/ece3.7308. eCollection 2021 May.
Age-related changes in survival and reproduction are common in seabirds; however, the underlying causes remain elusive. A lack of experience for young individuals, and a decline in foraging performance for old birds, could underlie age-related variation in reproduction because reproductive success is connected closely to provisioning offspring. For seabirds, flapping flight during foraging trips is physiologically costly; inexperience or senescent decline in performance of this demanding activity might cap delivery of food to the nest, providing a proximate explanation for poor breeding success in young and old age, respectively. We evaluated the hypothesis that young and old Nazca boobies (), a Galápagos seabird, demonstrate deficits in foraging outcomes and flight performance. We tagged incubating male and female adults across the life span with both accelerometer and GPS loggers during the incubation periods of two breeding seasons (years), during the 2015 El Niño and the following weak La Niña. We tested the ability of age, sex, and environment to explain variation in foraging outcomes (e.g., mass gained) and flight variables (e.g., wingbeat frequency). Consistent with senescence, old birds gained less mass while foraging than middle-aged individuals, a marginal effect, and achieved a slower airspeed late in a foraging trip. Contrary to expectations, young birds showed no deficit in foraging outcomes or flight performance, except for airspeed (contingent on environment). Young birds flew slower than middle-aged birds in 2015, but faster than middle-aged birds in 2016. Wingbeat frequency, flap-glide ratio, and body displacement (approximating wingbeat strength) failed to predict airspeed and were unaffected by age. Sex influenced nearly all aspects of performance. Environment affected flight performance and foraging outcomes. Boobies' foraging outcomes were better during the extreme 2015 El Niño than during the 2016 weak La Niña, a surprising result given the negative effects tropical seabirds often experience during extreme El Niños.
与年龄相关的生存和繁殖变化在海鸟中很常见；然而，其潜在原因仍然难以捉摸。年轻个体缺乏经验，以及老年鸟类觅食能力下降，可能是繁殖方面与年龄相关变化的基础，因为繁殖成功率与为后代提供食物密切相关。对于海鸟来说，觅食过程中的振翅飞行生理成本很高；这项高要求活动中缺乏经验或机能衰退可能会限制食物运回巢穴，分别为幼年和老年繁殖成功率低提供了直接解释。我们评估了这样一个假设：加拉帕戈斯海鸟 Nazca 鲣鸟的幼年和老年个体在觅食结果和飞行性能方面存在缺陷。在两个繁殖季节（年份）的孵化期，即 2015 年厄尔尼诺期间及随后的弱拉尼娜期间，我们用加速度计和 GPS 记录仪对不同年龄段正在孵化的成年雌雄 Nazca 鲣鸟进行了标记。我们测试了年龄、性别和环境对觅食结果（如体重增加）和飞行变量（如振翅频率）变化的解释能力。与衰老一致的是，老年鸟类在觅食时体重增加比中年个体少，这是一个边缘效应，并且在觅食行程后期空速较慢。与预期相反，幼年鸟类除了空速（取决于环境）外，在觅食结果或飞行性能方面没有缺陷。2015 年幼年鸟类飞行速度比中年鸟类慢，但在 2016 年比中年鸟类快。振翅频率、扑翼-滑翔比和身体位移（近似振翅强度）无法预测空速，且不受年龄影响。性别几乎影响了性能的所有方面。环境影响飞行性能和觅食结果。2015 年极端厄尔尼诺期间 Nazca 鲣鸟的觅食结果比 2016 年弱拉尼娜期间更好，鉴于热带海鸟在极端厄尔尼诺期间经常受到负面影响，这一结果令人惊讶。
