How do helpers help? Helper contributions throughout the nesting cycle in the cooperatively breeding brown-headed nuthatch

摘要

Breeder investment in offspring reflects a trade-off between the benefits realized from current reproductive efforts and the benefits expected from future reproductive opportunities. When assisted by nonbreeding helpers that provide care for offspring, breeders may modify reproductive investments to minimize the costs of producing offspring, or in ways that maximize productivity and offspring survival. How helpers assist breeders can vary with different stages of reproduction, and how breeders alter investment in response to helpers may change depending on the stage of reproduction. We assessed how helpers contribute to reproduction and how breeders alter their investment in response to helper contributions in the cooperatively breeding brown-headed nuthatch (Sitta pusilla). We assessed helper contributions across three stages of reproduction: (1) nest excavation, (2) maternal egg production, and (3) nestling care and development at days 8-12 post-hatching, a period of rapid nestling growth. We also investigated how breeders responded to helper contributions and the relationship of helper behavior with breeders' reproductive success. Helpers contributed to offspring care but not nest excavation. Breeders assisted by helpers did not alter investments in nest excavation, offspring production, or offspring care. As a result, offspring raised by cooperative groups received more food and weighed more. Nests with helpers were more likely to fledge at least one offspring, even when considering variation in territory characteristics and breeder experience. Results indicate breeders likely benefit from the favorable breeding conditions helpers provided for current breeding efforts, which influenced the quality of offspring produced and their likelihood of fledging in this study.