Hot droughts compromise interannual survival across all group sizes in a cooperatively breeding bird

Climate change is affecting animal populations around the world and one relatively unexplored aspect of species vulnerability is whether and to what extent responses to environmental stressors might be mitigated by variation in group size in social species. We used a 15-year dataset for a cooperatively-breeding bird, the southern pied babbler Turdoides bicolor, to determine the impact of temperature, rainfall, and group size on body mass change and interannual survival in both juveniles and adults. Hot and dry conditions were associated with reduced juvenile growth, mass loss in adults, and compromised survival between years in both juveniles (86% reduction in interannual survival) and adults (60% reduction in interannual survival). Individuals across all group sizes experienced similar effects of climatic conditions. Larger group sizes may not buffer individual group members against the impacts of hot and dry conditions, which are expected to increase in frequency and severity in future.

气候变化正影响全球各地的动物种群，而关于物种脆弱性的一个尚未得到充分探索的研究维度，是社会性物种种群规模的变化是否、以及在多大程度上能够缓解个体对环境压力的响应。本研究依托针对合作繁殖鸟类——南斑鸫鹛（Turdoides bicolor）的15年数据集，探究温度、降雨量与种群规模对幼鸟和成鸟的体重变化及年际存活率的影响。结果表明，炎热干旱的环境条件与幼鸟生长速率下降、成体体重减轻，以及幼鸟（年际存活率降低86%）和成鸟（年际存活率降低60%）的年际存活率下降均存在关联。无论种群规模大小，个体均会受到气候条件的相似影响。未来预计炎热干旱事件的发生频率与强度均会上升，而更大的种群规模或许无法为种群内个体抵御此类环境压力提供缓冲。