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Research from the University of Sussex out today (21 April 2026) has discovered widespread contamination by pesticides, commonly found in pet flea and tick treatments, in the feathers, eggs and even chicks of wild birds.

 The two new studies, funded by the conservation charity SongBird Survival, raise urgent questions about the environmental risks posed by veterinary treatments that are applied to millions of UK pets every year.

 UK Government ministers are currently investigating whether these products, which can currently be sold anywhere and do not require any professional advice from vets or suitably qualified persons on their use, should be restricted to distribution only by veterinary practitioners or pharmacists. The Government has also said it will launch an education campaign for pet owners on responsible use from spring 2026.

In the first study, researchers analysed 74 feather samples from five common UK garden birds: blackbirds, blue tits, chaffinches, dunnocks and goldfinches. Every sample contained pesticides, with a high prevalence of chemicals linked to household pet flea treatments, including:

• Imidacloprid (a neonicotinoid) in 88% of samples, banned from plant protection in the EU in 2018
• Fipronil in 72% of samples, banned for agricultural use in the EU since 2014

In addition, chlorpyrifos - a pesticide which has been illegal in the EU since 2020 - was found in 96% of samples, suggesting long-term persistence in UK environments.

The second study tested unhatched eggs and chicks found dead in their nests, screening for 20 pesticides. The majority contained at least one chemical used in pet flea treatments, with fipronil sulfone, fipronil and imidacloprid appearing most frequently.

Researchers have called for further studies to understand more about how these birds are exposed to pesticides, and how this exposure is impacting bird health and welfare.

Lead researcher Dr Cannelle Tassin de Montaigu, Research Fellow at the University of Sussex’s School of Life Sciences said: “This research shows for the first time that chemicals commonly found in flea and tick treatments are transferring from contaminated nest material to unhatched eggs and dead chicks. We have also found these chemicals in samples of common garden bird feathers.

“These findings highlight the need to evaluate the environmental safety of veterinary products and their potential impact on wildlife, particularly given the frequent, year-round application of these treatments which may contribute to a chronic and largely overlooked source of chemical exposure.”  

Previous research released last year by the University of Sussex revealed the widespread contamination of birds’ nests with chemicals from pet flea treatments. This latest study provides the first direct evidence in wild birds that these chemicals are transferring from contaminated nesting material into eggs and body tissue.

Sue Morgan, Chief Executive Officer, SongBird Survival said: “Finding pesticides from flea and tick treatments on common garden birds feathers, and within songbird eggs and chicks, is deeply alarming, especially as the UK faces a growing songbird crisis. As pet owners, we need to have confidence that we can protect our pets and own health, without harming wildlife.”

The University of Sussex and SongBird Survival are urging government to accelerate plans to address rising levels of fipronil and imidacloprid in the environment. Charities and academics, including the RSPB and the Wildlife Trusts, have signed an open letter to the Environment Secretary detailing their concerns.

Sue Morgan, Chief Executive, SongBird Survival added: “The Government must urgently assess the environmental impact of spot-on flea and tick products and strengthen regulation. An effective first step would be to make them prescription-only, ensuring access is maintained but with proper veterinary guidance. A label on a box isn’t enough. We need informed conversations between vets and pet owners to protect pets, homes and the environment.”

Over 80% of UK cats and dogs receive at least one flea or tick treatment per year, with many pet owners applying spot-on treatments monthly on a preventative basis. Previous research from the University of Sussex  has already shown that chemicals from these treatments reach waterways and household drains, with handwashing identified as the largest source of emissions. 

Fipronil or imidacloprid were detected on the hands of all pet owners tested for at least 28 days after a spot-on application, indicating that despite guidelines advising minimal contact until the site is dry, contamination occurs continuously throughout the product’s active period.

Vet Sustain Director and Chair, Ed Bailey, said "This important research adds to a growing body of evidence that pet parasiticides are entering the environment. Whilst further evidence is still needed on the impacts of these chemicals on ecosystems and wildlife health and welfare, Vet Sustain supports the precautionary principle and risk-based approach to prescribing pet parasites. Vet Sustain's independent risk-based decision tools are available to support veterinary professionals to assess parasite risk in cats and dogs, to protect animal, human and environmental health."

Professor Dave Goulson, Professor Of Biology at the University of Sussex, said: “It was deeply concerning to discover that potent insecticides, long-banned in agriculture but still used as spot-on flea and tick treatments on pets, are widely contaminating rivers and are also found in blue tit and great tit eggs and chicks and in feathers of adult songbirds.

This widespread environmental contamination is unacceptable. Defra need to take regulatory steps to sort this mess out as a matter of urgency.”

 This work supports the UN’s Sustainable Development Goal: SDG 15 (life on land). You can read more about our work on the SDGs here.