Songbirds being killed by pesticides found in pet fur flea treatments

Songbird chicks are being killed by high levels of pesticides in the pet fur used by their parents to line their nests, a study has found.

Researchers surveying nests for the harmful chemical found in pet flea treatments found that it was present in every single nest. The scientists from the University of Sussex are now calling for the government to urgently reassess the environmental risk of pesticides used in flea and tick treatments and consider restricting their use.

Cats and dogs are widely treated with insecticides to prevent against fleas. Vets often recommend regular flea treatments as a preventive measure, even when dogs and cats do not have the pest. But scientists now recommend animals should not be treated for fleas unless they actually have them.

It was already widely known that the chemicals in the treatments were affecting life in rivers and streams after pets swam in them, but the discovery of songbird nest contamination will add to the pressure.

Cannelle Tassin de Montaigu, the lead author of the research paper, said: “No nest was free from insecticides in our study, and this significant presence of harmful chemicals could be having devastating consequences on the UK’s bird populations.

“Our research shows that based on the chemicals detected, veterinary flea and tick drugs are the most likely source of contamination. We undertook our research when it was safe to do so at the end of the breeding season, so the problem could in fact be much worse. This raises questions about the environmental impact of veterinary drugs and calls for a comprehensive environmental risk assessment of veterinary treatments.”

The study, funded by the charity SongBird Survival and published today in Science of the Total Environment, shows that the fur used by birds to build the inner lining of their nests contained chemicals used in pet flea treatments, such as fipronil.

The researchers collected 103 blue and great tit nests that were lined with fur, finding that 100% of the nests contained fipronil, which is banned in the UK and EU for agricultural use, and 89% contained imidacloprid, which was banned in the EU as a plant protection product in 2018. Both are still widely used in pet flea treatments. The UK government is drawing up plans for a total ban on imidacloprid in agriculture but not for pet treatments. The researchers also detected 17 out of the 20 insecticides they were testing for.

The scientists found a higher number of unhatched eggs or dead chicks in nests where there was a higher incidence of insecticide.

Recent research has found that these flea treatments also enter rivers, killing the wildlife within, and that pet owners using them risk contaminating their hands with the chemicals for at least 28 days after the treatment has been applied.

Sue Morgan, the chief executive of SongBird Survival, said: “We are a nation of pet lovers and bird lovers, and it is extremely concerning to see the alarming levels of toxic pesticides in bird nests from veterinary drugs. Pet owners will be upset to hear that in trying to do the right thing to support their pets with fleas and ticks, they could be harming our ecosystem, resulting in dead newborn chicks and unhatched eggs. As pet owners, we need to have confidence that we are keeping our pets well, without devastating impacts on our wildlife.

“Our UK songbirds are in crisis. More than half of our UK songbirds are threatened or already in decline, which is why this latest research shows the importance of taking action as soon as possible. We want the government to undertake a more comprehensive environmental risk assessment of veterinary drugs.”

This article by Helena Horton was first published by The Guardian on 27 January 2025. Lead Image: Fipronil is banned for agricultural use in the UK, but is still widely used to stop pets getting fleas, ending up in the nests of songbirds such as blue tits.
Photograph: Geoffrey Swaine/Rex/Shutterstock.

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