Data from: Nest survival in year-round breeding tropical Red-capped Larks (Calandrella cinerea) increases with higher nest abundance but decreases with higher invertebrate availability and rainfall

Nest survival is critical to breeding in birds and plays an important role in life-history evolution and population dynamics. Studies evaluating the proximate factors involved in explaining nest survival and the resulting temporal patterns are biased in favor of temperate regions. Yet, such studies are especially pertinent to the tropics, where nest predation rates are typically high and environmental conditions often allow for year-round breeding. To tease apart the effects of calendar month and year, population-level breeding activity and environmental conditions, we studied nest survival over a 64-month period in equatorial, year-round breeding red-capped larks Calandrella cinerea in Kenya. We show that daily nest survival rates varied with time, but not in a predictable seasonal fashion among months or consistently among years. We found negative influences of flying invertebrate biomass and rain on nest survival and higher survival of nests when nests were more abundant, which suggests that nest predation resulted from incidental predation. Although an increase in nest predation is often attributed to an increase in nest predators, we suggest that in our study, it may be caused by altered predator activity resulting from increased activity of the primary prey, invertebrates, rather than activity of the red-capped larks. Our results emphasize the need to conduct more studies in Afro-tropical regions because proximate mechanisms explaining nest predation can be different in the unpredictable and highly variable environments of the tropics compared with the relatively predictable seasonal changes found in temperate regions. Such studies will aid in better understanding of the environmental influences on life-history variation and population dynamics in birds.鸟巢存活率（nest survival）对于鸟类繁殖至关重要，同时在鸟类生活史演化与种群动态研究中占据重要地位。旨在阐明鸟巢存活率及其相关时间格局的近因因素研究，在研究区域分布上偏向温带地区，存在明显的区域偏向。然而此类研究对于热带地区尤为关键：热带区域的鸟巢捕食率普遍偏高，且环境条件通常支持全年繁殖。为厘清公历月份、年份、种群级繁殖活动以及环境条件各自的影响效应，我们针对肯尼亚赤道地带全年繁殖的红顶短趾百灵（Calandrella cinerea）开展了为期64个月的鸟巢存活率研究。研究结果显示，鸟巢日存活率随时间波动，但并未在月份间呈现可预测的季节性规律，也未在各年份间保持一致趋势。我们发现，飞行无脊椎动物生物量与降雨量对鸟巢存活率存在负向影响；而当鸟巢密度升高时，其存活率反而更高，这表明鸟巢捕食属于偶发捕食事件。尽管巢捕食率上升通常被归咎于捕食者种群规模扩大，但本研究认为，本研究中的捕食率上升可能由主要猎物——无脊椎动物的活动增强所引发的捕食者行为改变所致，而非红顶短趾百灵自身活动的影响。本研究结果强调，需在非洲热带区域开展更多同类研究：相较于温带地区相对可预测的季节变化，热带地区环境不可预测且高度多变，解释鸟巢捕食的近因机制可能存在显著差异。此类研究将有助于更深入地理解环境因素对鸟类生活史变异与种群动态的影响。