Songbird nests are being contaminated by insecticides applied to pets. The compounds frequently found in shampoos, spot-on treatments or impregnated collar flea treatments for cats and dogs were identified in fur taken from the nests of blue tits and great tits in the UK. These pesticides have now been linked to a higher chance of these songbirds’ eggs failing to hatch and chicks dying in the nest.
Over 27 tonnes of fipronil and 33 tonnes of imidacloprid have been sold for companion animal parasite treatment in the UK since the 1990s. ‘Flea treatments for companion animals don’t have a thorough environmental risk assessment, unlike for agricultural pesticides,’ says Cannelle Tassin de Montaigu, an ecologist at the University of Sussex, UK, who carried out the research. She wants to see this change in Europe.
The investigation identified 17 out of 20 insecticides screened for in nesting material, with between two and 11 insecticides per nest. All 103 nests examined – collected by volunteers from the British Trust for Ornithology (BTO) – contained fipronil, an insecticide common in flea treatments. ‘About 74% of woodland European birds use fur as a nest-lining material,’ Tassin de Montaigu notes. ‘In cities, it’s most likely to come from cats and dogs.’
Imidacloprid and permethrin were each detected in 89% of samples. The average concentration of fipronil, imidacloprid and permethrin was 116 nanograms per millilitre (ng/ml), 376ng/ml and 231ng/ml, respectively. One nest contained dinotefuran – a neonicotinoid used to prevent fleas and ticks in vet products – at 7198ng/ml, the highest concentration in a single sample.
The team also discovered more dead offspring or unhatched eggs in nests containing a higher number or a higher concentration of certain insecticides. Contact exposure of eggs or chicks to insecticides in nest lining may lead to fewer chicks fledging, the study suggests, as well as ingestion of these substances.
The study does not definitively prove that contaminated fur brought into the nest by parent birds caused harm to eggs or chicks, however. ‘The higher mortality in nests with more insecticides is a correlation, not necessarily causation,’ Tassin de Montaigu explains. ‘If this is the cause, however, it could have devastating consequences for not just blue tits or great tits, but for many other bird species.’
‘Whilst the findings are not surprising it is an important piece of work, confirming suspicions with hard, quantitative data,’ comments Kathleen Lewis, an agricultural chemist at the University of Hertfordshire, UK. ‘Fipronil and permethrin would be my main concerns as they are so commonly used in and around homes,’ she notes. Many parasites are now resistant to fipronil, she adds.
‘All the bird studies I’ve done on imidacloprid and other neonicotinoids are from agricultural landscapes where birds may consume contaminated insects or treated seeds,’ says Christy Morrissey, an avian ecotoxicologist at the University of Saskatchewan, Canada. She believes skin contact could be important in the UK study. ‘Young birds are naked and their skin is very, very thin and heavily vascularised. It seems plausible that the chemicals could move from the fur in the nest across [chicks’] skin,’ Morrissey says.
Morrissey would like to see tests performed on tissue samples from chicks to check insecticide levels and help prove cause and effect. There are currently no published studies on the effects of skin exposure to systemic insecticides in small songbirds.
Neonicotinoids have been banned for use on outdoor crops in the EU since 2018, while fipronil was banned for agricultural uses in 2013. The UK is pressing ahead with a complete ban on agricultural neonicotinoid use.
Hazel McCambridge at the BTO, who helped with nest collection for the study, says fur has fantastic insulation properties, ‘so do put it out in the garden for birds to collect’. However, she recommends that pet owners dispose of cat and dog hair in the bin if they use a spot-on treatment.
‘This study is a stark reminder of just how prevalent toxic chemicals are in the environment and the damaging impact they can have on wildlife,’ said Beccy Speight, chief executive of the Royal Society for the Protection of Birds. ‘The UK government’s recent decision to uphold the ban on the use of neonicotinoids in farming was a positive step, but as this paper shows, more action is needed to limit the exposure of wildlife to chemicals from other sources.’
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