How do helpers help? Helper contributions throughout the nesting cycle in the cooperatively breeding brown-headed nuthatch
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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.
Helpers may contribute to breeders’ reproductive effort during many stages of reproduction. The presence of nonbreeding helpers should therefore influence the investments made by breeders during different stages of breeding. Investment decisions in one stage should furthermore influence later investment decisions. We demonstrated that helpers assisted breeders primarily during the offspring rearing stage in brown-headed nuthatches (Sitta pusilla), a facultative cooperative breeder. Breeders with helpers maintained their level of investments in offspring similar to the investments documented for breeders without helpers. As a result, chicks in nests with helpers received more food and were heavier, and adults with helpers were more likely to fledge at least one young. Our results suggest that the combined effects of parental and helper investment provided benefits for current broods with potentially important survival consequences for offspring.
KeywordsFeeding behavior Parental investment Helper effects Helpers-at-the-nest Fitness benefits Reproductive success
Many volunteers and field assistants contributed to the fieldwork for this long-term study. Special thanks to A. Janik, A. Kreuser, J. Botero, D. McElveen, M. Gray, E. Schunke, A. Doyle, D. Pavlik, B. Williams, D. Smith, and H. Levy for exceptional fieldwork. The authors thank the editor and anonymous reviewers for their helpful suggestions and comments on the manuscript.
Funding was provided by the Florida State University Brenda Weems Bennison Endowment, the Florida State University Robert B. Short Zoology Scholarship, and the Wildlife Research Endowment at Tall Timbers Research Station. JAC was supported in part by a fellowship from Tall Timbers Research Station. EHD was supported in part by NSF grant 1453408.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable national and institutional guidelines for the care and use of animals were followed. All procedures performed were in accordance with the ethical standards approved by the Florida State University Animal Care and Use Committee (protocol 1505) and by the Tall Timbers Institutional Animal Care and Use Committee (protocol 1042). There has been no evidence of any effects of marking, handling, nest monitoring, or methodology on the behavior and survival of individuals in the study population.
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