Veterinary insecticides detected in wild bird nests across urban and forest habitats
Researchers detected multiple veterinary insecticides — including fipronil, imidacloprid, and permethrin — in Great Tit nest materials collected from urban and protected forest sites in Hungary during the 2025 breeding season. The compounds, commonly used in flea and tick treatments for pets, are thought to enter bird nests via animal fur incorporated into nest linings. The findings reveal a previously unrecognized pathway by which companion animal treatments may expose wildlife, even in protected ecosystems.
A study published on bioRxiv analyzed nest material from 63 Great Tit (Parus major) nests in artificial nest boxes at an urban site and a nearby protected forest in Hungary during the 2025 breeding season. Using HPLC-MS/MS and GC-MS analytical methods, researchers identified fipronil, fipronil sulfone, imidacloprid, permethrin, and acetamiprid in nest materials, with acetamiprid found exclusively in urban nests — suggesting additional non-veterinary sources in urban environments. Urban nests showed higher contamination levels and greater compound diversity than forest nests, though residues were detected at both sites. Insecticide residues were present at both mid-nestling and post-fledging sampling stages but declined over the course of the breeding cycle. Notably, the detected contamination was not statistically associated with measurable reproductive outcomes in the birds. The authors highlight that many of these synthetic insecticides are restricted for agricultural use in the EU due to environmental concerns, yet remain widely available in veterinary products, creating an underappreciated route of wildlife exposure. The study calls for broader ecological risk assessments of veterinary insecticide use, particularly given their potential to reach protected natural areas.
What's missing
As a preprint, this study has not yet undergone peer review, and its findings should be interpreted with caution. The study does not assess whether detected insecticide concentrations in nests reach toxicologically relevant doses for nestlings or adults, nor does it measure direct uptake or internal exposure levels in the birds. The geographic scope is limited to a single urban-forest pair in Hungary, which may limit generalizability. Long-term or sublethal effects on bird health and behavior beyond the measured reproductive parameters remain unexamined.
What different sources said
- bioRxivCenter
Veterinary insecticides in wild bird nests: emerging contaminants in urban and protected forest habitats
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