How helpers help: disentangling ecological confounds from the benefits of cooperative breeding

Evolutionary explanations for helping in cooperative breeding systems usually require a positive effect of helping on the fitness of the breeders being assisted. However, such helper effects have proven surprisingly difficult to quantify. Cockburn et al . (this issue ) apply detailed statistical analyses to long-term field data on the enigmatic superb fairy-wren. They show that it is possible to disentangle the complex web of ecological and evolutionary interactions that confound so many studies. Whilst fairy-wren helpers may not increase nest productivity, they do increase future survival of breeding females. This study points the way for future statistical explorations of long-term data in other cooperative birds and mammals.