Pet Flea Treatments Are Poisoning Wild Birds: Study

High levels of harmful pesticides from pet flea treatment in birds’ nests lined with animal fur is leading to the increased mortality rate of chicks.

A recent study reveals that pet flea and tick treatments are poisoning wild birds. The study found that songbirds that collect and line their nests with pet fur are at greatest risk.

“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,” said the study’s lead author, ecotoxicologist Cannelle Tassin de Montaigu, a post-doctoral researcher at the University of Sussex, where she specializes in ecotoxicology and conservation ecology.

“Our research shows that, based on the chemicals detected, veterinary flea and tick drugs are the most likely source of contamination,” Dr Tassin de Montaigu added.

Dr Tassin de Montaigu and collaborators came to this conclusion after analyzing 103 blue tit and great tit nests for the presence of 20 different insecticides. They detected 17 of these poisons in the fur that the birds used to line their nests. The nests were collected by British Trust for Ornithology volunteers as part of the Nesting Neighbour Scheme.

Dr Tassin de Montaigu and collaborators identified anywhere from 2 to 11 different insecticides in each nest, including fipronil, which was present in 100% of the nests, and imidacloprid and permethrin in 89% of the nests. Fipronil is banned in both the UK for agricultural use (more here) and in the USA as a “possible human carcinogen” (more here – USA information for these poisons is included for my American readers). Imidacloprid has been banned for agricultural use since 2018 by the European Food Safety Authority (EFSA) because it represents a risk to wild bees and honeybees (more here). Apparently, imidacloprid is not banned in the USA, although some states do restrict its use. Permethrin has been partially banned for agricultural uses in the EU (more here) and is listed as a “restricted use” substance by the US Environmental Protection Agency (EPA) due to its high toxicity to aquatic organisms (more here).

And yet, despite all these known dangers to wildlife and to the environment, all three pesticides are still widely used in tick and flea treatments for pets. Pet owners often make matters worse by grooming their pets outdoors.

“Many pet owners leave fur outdoors after brushing their pet, hoping it will be used by birds like blue tits and great tits to line their nests,” Dr Tassin de Montaigu said in email.

“While this practice may seem harmless and even helpful, our study has found that chemicals commonly used in animal flea and tick treatments (e.g., fipronil, imidacloprid, permethrin) make their way into birds’ nests. These substances, often banned for agricultural use due to their environmental risks, are still widely used in veterinary applications,” Dr Tassin de Montaigu said in email.

These poisons are commonly be found in shampoos, sprays, and spot-on treatments for pets and/or livestock.

Dr Tassin de Montaigu and collaborators reported there was clear evidence that these insecticides are harmful to wild birds. Contaminated birds’ nests contained a higher number of unhatched eggs or dead chicks – and the numbers of dead rose as the number of insecticides increased, as the total concentration of insecticides increased, or in nests with a higher concentration of fipronil, imidacloprid or permethrin (Figure 3). This suggests that exposure of birds’ eggs to insecticides in pet fur nest linings can lead to mortality and lower reproductive success.

What surprised you most about these findings?

“What was most surprising was that no nests were free of insecticides,” Dr Tassin de Montaigu told me in email.

Equally concerning was the high concentrations of pesticides in each nest – even months after breeding season had ended and the surviving chicks had fledged.

“The levels observed were also worrying, especially that we collected the fur from nests months after the breeding season, therefore the levels of residues we observed are likely lower than what was present in the nest back in spring of that year.”

“As awareness of this issue grows, pet owners, scientists and policymakers all have a role to play in ensuring that veterinary treatments do not come at the cost of the wildlife,” Dr Tassin de Montaigu told me in email.

“With careful consideration and responsible use of flea treatments, it may be possible to protect both pets and wildlife. The most important part is for the government to ensure there is a greater environmental risk assessment of veterinary drugs, especially concerning companion animals.”

More than half of all UK songbirds are threatened or in decline, so it is crucial that pet owners, scientists and policy makers act quickly to prevent further harm.

“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,” said Susan Morgan, Chief Executive of Songbird Survival, which funded the study. “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.”

Is there a safer alternative to the poisons currently used by the pet industry?

“We cannot confirm that an alternative is safer, simply because there is no research on it, not yet at least,” Dr Tassin de Montaigu replied in email.

It’s important to note that flea treatments for pets are typically overused.

“Additionally, most cats and dogs don’t need to be treated for fleas and ticks, especially in winter months, when fleas and ticks are scarce,” Dr Tassin de Montaigu explained in email.

“The preventive usage of flea treatment is the issue: if your pet does not have fleas then why treat it? This can be checked regularly while brushing or with a special comb,” Dr Tassin de Montaigu elaborated in email. “We would not treat children for lice every month just as a prevention, why do it with pets?”

Source:

Cannelle Tassin de Montaigu, Gaetan Glauser, Sylvie Guinchard and Dave Goulson (2025). High prevalence of veterinary drugs in bird’s nests, Science of The Total Environment, 964:178439 | doi:10.1016/j.scitotenv.2025.178439

---

© Copyright by GrrlScientist | hosted by Forbes | LinkTr.ee

Socials: Bluesky | CounterSocial | Gab | LinkedIn | Mastodon Science | Spoutible | SubStack | Threads | Tribel | Tumblr | Twitter