Cooperative breeding does not mitigate declines in offspring care with cool and wet conditions in a temperate Australian songbird.

Adverse climatic conditions can decrease reproductive success by reducing parents' ability to provide enough resources to growing young. Here, we address the hypothesis that helpers at the nest can buffer the negative effects of challenging climatic (cool and wet) conditions in cooperatively breeding superb fairy-wrens. We first established that public records are adequate to quantify climate effects: temperatures recorded at a nearby meteorological station explained total offspring care equally well as microclimate temperatures measured inside the nest and near the nest site. We then compared the effects of temperature and rainfall on offspring care in pairs with and without helpers and found that (i) at lower, more energetically challenging temperatures, nestlings receive larger prey and more prey biomass, and females brood young nestlings more, but these increases in care occur regardless of helper presence; (ii) groups with helpers provide more prey biomass during dry conditions, but higher rainfall in the previous week reduces this to the level of unassisted pairs. Overall, cooperative breeding in superb fairy-wrens does not appear to buffer challenging (cool and wet) conditions: helpers do not mitigate the effects of cool temperatures and although groups with helpers deliver more food, this benefit disappears during periods with high rainfall.