Disentangling climatic and nest predator impact on reproductive output reveals adverse high‐temperature effects regardless of helper number in an arid‐region cooperative bird

Climate exerts a major influence on reproductive processes, and an understanding of the mechanisms involved and which factors might mitigate adverse weather is fundamental under the ongoing climate change. Here, we study how weather and nest predation influence reproductive output in a social species, and examine whether larger group sizes can mitigate the adverse effects of these factors. We used a 7‐year nest predator‐exclusion experiment on an arid‐region cooperatively breeding bird, the sociable weaver. We found that dry and, especially, hot weather were major drivers of nestling mortality through their influence on nest predation. However, when we experimentally excluded nest predators, these conditions were still strongly associated with nestling mortality. Group size was unimportant against nest predation and, although positively associated with reproductive success, it did not mitigate the effects of adverse weather. Hence, cooperative breeding might have a limited capacity to mitigate extreme weather effects. We used an experimental nest predator exclusion to study the effects of weather and nest predation on reproductive output in a cooperatively breeding bird endemic to the Kalahari region. Our main aim was to determine whether helpers‐at‐the‐nest could reduce nestling mortality under adverse conditions. We found that hot and dry conditions are major drivers of nestling mortality, often through their influence on nest predation, and that helpers decrease overall nestling mortality but appear ineffective against predators and extreme weather events.