Cooperative breeding in birds increases the within-year fecundity mean without increasing the variance: A potential mechanism to buffer environmental uncertainty

Cooperative breeding is a common strategy of vertebrates under harsh, unpredictable environments. Yet we do not fully understand the demographic mechanisms by which these species buffer environmental challenges, because while cooperation typically increases the fitness mean, whether it alters the variance to further reduce the population risk of stochastic extinction is unclear. We addressed this issue using a meta-analysis among avian cooperative breeders. Compared with their non-cooperative counterparts in the same populations, cooperative pairs on average fledged more offspring, without increasing the fecundity variance accordingly. This pattern held when failed nests were excluded from analysis to filter the effect of nest predation on the estimation of brood size at fledging, retaining the effect of brood reduction (the partial loss of nestlings in a brood). Cooperative pairs did not differ in the mean and variance of clutch size from non-cooperative pairs; the former had a lower l..., , # Data from: Cooperative breeding in birds increases the within-year fecundity mean without increasing the variance: A potential mechanism to buffer environmental uncertainty [Access this dataset on Dryad](https://doi.org/10.5061/dryad.k0p2ngfk3) This dataset supports a meta-analysis on the effects of cooperative breeding on fecundity mean and variance in birds. It includes pooled and year-specific reproductive data, a phylogenetic tree file, and analysis scripts. ## Description of the data and file structure We conducted a literature search on ISI Web of Science up to October 1, 2023, for studies on cooperative breeding in birds. Search terms included the names of 821 cooperatively breeding altricial species and related keywords. Citation Searching was also employed. Studies were included if they provided means and SD or SE for clutch size and brood size at fledging for both cooperative and non-cooperative nests, with at least four nests per phenotype. For detailed methods, see the...,