Data from: Impacts of nest predators and weather on reproductive success and population limitation in a long-distance migratory songbird

Although avian nesting success is much studied, little is known about the relative importance of the factors that contribute to annual reproductive success and population limitation, especially for long-distance migratory songbird species. We combined a field experiment limiting access to nests by mammalian predators with modeling of long-term field data of American redstarts (Parulidae: Setophaga ruticilla) to assess the effects of multiple environmental variables on breeding success and population limitation. Experimental treatment (baffles placed around tree boles beneath active nests; n = 71) increased nesting success of this single-brooded species significantly (77 vs 50% in controls; n = 343), demonstrating that scansorial mammals, primarily red squirrels Tamiasciurus hudsonicus and eastern chipmunks Tamias striatus, reduced reproductive success. Based on unbaffled nests (n = 466), daily nest survival varied annually, and was positively influenced by May temperature and negatively by sciurid nest predator abundance. Daily nest survival was also influenced positively by June rainfall, and declined with nest age but not with calendar date. Since nest failure was overwhelmingly caused by nest predation, these significant climate and nest-age effects in our models are indirect, likely influencing nest predator and/or nesting bird behaviors that in turn influenced nest predation. Redstart population density had no effect on nesting success, after accounting for other factors. Annual reproductive success accounted for 34% of the variability in annual population change in redstarts in our study area. Our findings document 1) breeding season population limitation in this species, 2) a link between tree masting and bird population dynamics via mammal population fluctuations, 3) the independent contributions of summer versus winter population processes in a migratory species, and 4) the potential complexity of climate-biotic interactions.尽管学界对鸟类筑巢成功率已有较为广泛的研究，但对于影响年度繁殖成功率与种群限制的各类因素的相对重要性，我们仍所知甚少，针对长距离迁徙鸣禽类群而言尤其如此。本研究结合了一项限制哺乳类捕食者接触巢穴的野外实验，以及美洲红尾鸲（森莺科：Setophaga ruticilla）的长期野外监测数据建模工作，以评估多种环境变量对繁殖成功率与种群限制的影响。实验处理组（在活跃巢穴下方的树干外周安装防兽挡板，样本量为71）显著提升了该单窝繁殖物种的筑巢成功率：处理组筑巢成功率达77%，对照组为50%，对照组样本量为343。该结果证实，以北美红松鼠（Tamiasciurus hudsonicus）和东部花栗鼠（Tamias striatus）为代表的攀援哺乳类会降低该物种的繁殖成功率。基于未安装防兽挡板的巢穴监测数据（样本量为466），每日巢存活率存在年际波动，且与五月平均气温呈正相关，与松鼠科巢捕食者的种群丰度呈负相关。此外，每日巢存活率还与六月降雨量呈正相关，并随巢龄增加而降低，但与观测日历日期无显著关联。由于巢穴失败绝大多数由捕食行为导致，本研究模型中检测到的显著气候与巢龄效应均为间接效应，可能通过改变巢捕食者或筑巢鸟类的行为，进而对巢捕食压力产生影响。在控制其他变量的前提下，美洲红尾鸲的种群密度对筑巢成功率无显著影响。年度繁殖成功率可解释本研究区域内美洲红尾鸲年度种群变化中34%的变异量。本研究结果证实了以下四点：1）该物种存在繁殖季种群限制现象；2）通过哺乳类种群波动，树木种子大年结实与鸟类种群动态之间存在关联；3）迁徙物种种群的夏季与冬季过程各自独立发挥调控作用；4）气候-生物交互作用可能具备复杂的作用机制。