Long-term effects of habitat quality on juvenile fitness along contrasting environmental gradients

我的研究计划的长期目标是了解人为压力因素是如何导致迁徙鸣禽数量下降的。几十年来，数十种北美物种的数量急剧下降，许多物种现在被加拿大列为濒危物种。迁徙鸣禽保护面临的最大挑战之一是确定经过充分研究的繁殖种群与它们生命周期中其他地方的威胁之间的联系。2009年，我的实验室在《科学》杂志上发表了一项突破性的研究，首次使用微型跟踪设备绘制了鸣禽从开始到结束的迁徙地图，这引发了我们对鸣禽迁徙生态学和保护的理解的一场革命。然而，一个关键的知识缺口仍然存在，因为对候鸟幼鸟的生存知之甚少，但预计会对种群动态产生重大影响。幼崽在孵化后一个月左右就会离开父母的领地，变得越来越活跃，难以追踪，迁徙后很少有幼崽返回到离出生地足够近的地方，以至于被研究人员发现。环境压力因素预计会对独立的幼崽产生很大的影响，因为它们的觅食效率最初很低，但它们必须建立脂肪储备，为它们首次在数千公里的陌生地形上的秋季迁徙做准备。

The long term objective of my research program is to understand how anthropogenic stressors contribute to population declines of migratory songbirds. Dozens of North American species have been in steep decline for decades and many are now designated as Species at Risk in Canada. One of the biggest challenges in migratory songbird conservation has been determining the link between well-studied breeding populations and threats elsewhere in their life cycle. In 2009, my lab published a ground-breaking study in Science that used miniaturized tracking devices to map the start-to-finish migration of songbirds for the first time, and this triggered a revolution in our understanding of songbird migration ecology and conservation. However, a critical gap in knowledge remains because juvenile survival is poorly understood in migratory songbirds yet is expected to have a large impact on population dynamics. Offspring disperse away from their parent’s territory a month or so after hatching, become increasingly mobile and difficult to track, and after migration few return close enough to their natal site to be detected by researchers. Environmental stressors are expected to have a big impact on independent juveniles because their foraging efficiency is initially low yet they must build fat reserves to prepare for their inaugural fall migration that is thousands of kilometers across unfamiliar terrain. My research program is novel because I will track juveniles by deploying new long-lasting (>1 year) coded radio-transmitters within a new array of automated telemetry receivers that blankets southwestern Ontario. By combining manual and automated tracking, my students will test how habitat quality affects juvenile condition, survival, dispersal and onset of fall migration and we will re-locate recruits that return the next spring within the ~100,000 square kilometer array. This novel technology will allow us to test a series of hypotheses for how and why habitat quality impacts short-and long-term juvenile fitness in migratory songbirds. Poor habitat quality is expected to reduce nestling body condition and carry over to have long-lasting and negative effects on juvenile fitness. We will evaluate the nature and duration of these development effects along two contrasting environmental gradients (forest fragmentation, agricultural intensification) that differ in their underlying ecological stressors. Our results will directly inform habitat management decisions through population modelling scenarios that clearly identify the consequences of habitat loss and fragmentation on migratory songbirds.