Abstract
Bird–ant interactions are diverse but rarely tested experimentally, limiting their integration into ecological theory. One hypothesized but unverified benefit is ant-mediated parasite control in bird nests. Here, we present the first experimental evidence supporting this hypothesis in a wild system involving house sparrows (Passer domesticus), arboreal ants (Crematogaster scutellaris), and blood-feeding mites (Pellonyssus reedi). Using field ant-exclusion experiments, we show that ant presence reduces mite abundance and enhances chick growth early in the breeding season, but has detrimental effects later. Nestlings in ant-excluded nests also show consistently higher H/L ratios, indicating greater physiological stress. Structural equation modeling reveals that ant effects on nestling condition are indirect and mediated by mite load. Our findings provide the first causal demonstration of ant-mediated parasite suppression in birds, revealing that the outcome of this interaction is highly context-dependent. This work underscores the dynamic nature of species interactions and highlights overlooked ecological roles of ants in avian systems.
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Data availability
Raw data for analyses and figures are available in Zenodo at https://doi.org/10.5281/zenodo.15721917. All other data are available from the corresponding author on reasonable request.
Code availability
Codes for analyses and figures are available in Zenodo at https://doi.org/10.5281/zenodo.15721917.
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Acknowledgements
We are deeply grateful to Carmen González, Agustín Villar, María Vizcaíno, and the technical staff at CYCITEX for their invaluable support in facilitating this research at the Valdesequera experimental farm. We also thank three anonymous referees for their constructive comments. Our research was funded by the Spanish National Research Plan project PID2020-119576GB-I00. Angela Salido was funded by a predoctoral grant of the Spanish Ministry of Science and Innovation (PRE2021-099966).
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J.M.A., J.L.R.L., and D.P. conceived the original idea. J.M.A., A.S., and D.P. curated the data. J.M.A. did the analyses and wrote the first draft, and all authors reviewed and edited the manuscript.
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Avilés, J.M., Salido, Á., Reyes-López, J.L. et al. Phenology modulates the top-down control of ants on bird ectoparasites: from mutualism to antagonism.
Commun Biol (2025). https://doi.org/10.1038/s42003-025-09387-9
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DOI: https://doi.org/10.1038/s42003-025-09387-9
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