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.

尽管学界已对鸟类巢成功率开展了大量研究，但对于影响年度繁殖成功与种群限制的各类因素的相对重要性，我们仍知之甚少，针对长距离迁徙鸣禽类群的相关研究尤为匮乏。本研究结合了限制哺乳动物捕食者访问鸟巢的野外控制实验，以及美洲红尾鸲（Parulidae: Setophaga ruticilla）的长期野外数据建模工作，以探究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（在活跃鸟巢下方的树干周围安装防捕食挡板；样本量n=71）显著提升了该单窝繁殖物种的巢成功率（处理组为77%，对照组为50%；对照组样本量n=343），这表明攀援类哺乳动物——主要为北美红松鼠（Tamiasciurus hudsonicus）与东部花栗鼠（Tamias striatus）——会降低其繁殖成功率。基于未安装防捕食挡板的鸟巢数据（n=466），每日巢存活率存在年度差异：5月气温对其具有正向影响，而松鼠科巢捕食者的丰度则对其产生负向影响。6月降雨量同样对每日巢存活率具有正向促进作用，巢存活率随巢龄增加而下降，但不受日历日期的影响。由于绝大多数巢失败事件均由巢捕食导致，本研究模型中观测到的气候与巢龄显著效应属于间接效应，它们可能通过影响巢捕食者或筑巢鸟类的行为，进而作用于巢捕食过程。在控制其他变量的前提下，红尾鸲的种群密度对巢成功率无显著影响。在本研究区域内，年度繁殖成功程度可解释红尾鸲年度种群变化34%的变异量。本研究结果证实了四项核心发现：1）该物种存在繁殖季种群限制效应；2）通过哺乳动物种群波动，树木结实大年与鸟类种群动态之间存在关联；3）迁徙物种的夏季与冬季种群过程各自独立发挥作用；4）气候与生物因子的交互作用具有潜在的复杂性。