Rat poison does not stay with the rat. Predators and scavengers that eat poisoned or weakened rodents can take up the poison as well, which is why professional rodenticide use in Great Britain sits within a stewardship scheme. This article summarises the UK Centre for Ecology & Hydrology (UKCEH) report “Second Generation Anticoagulant Rodenticides (SGARs) in Mammals and Predatory Birds: An interspecies comparison” (Predatory Bird Monitoring Scheme, dated 26 February 2025) and the Campaign for Responsible Rodenticide Use (CRRU UK) website, the industry body that runs the stewardship regime. It reports monitoring findings at the strength the report supports: the data are observational, and the report itself says its comparisons have gaps. This is general information, not advice on treating a rodent problem.
What the report is
The report compares residues of five second-generation anticoagulant rodenticides (SGARs) in the livers of predatory birds and mammals collected across the UK, and assesses how residues changed after the conditions for using SGARs were revised in 2015 and after the industry-led stewardship regime began. It says avian and mammalian predators and scavengers are widely exposed to SGARs, likely through feeding on contaminated prey, which can include non-target animals. Its data come largely from carcasses sent in by the public and from other monitoring programmes, so they describe animals that were found and submitted, not a random sample of wildlife.
Which animals showed the most residue
The authors report that residues were significantly higher in generalist and scavenger birds and mammals than in other groups. Among the mean liver concentrations they tabulate, peregrine falcons, which mainly eat birds, were lowest (about 13 ng/g wet weight), barn owls and tawny owls, which eat small mammals, were intermediate (means of roughly 63 to 96 and 86 to 109 ng/g), and red kites, which scavenge, were highest among the birds (about 190 to 200 ng/g). The red fox had a very high mean of 993 ng/g. The report says the differences reflect feeding strategy and habitat, and that species also differ in their sensitivity to the poisons.
For other mammals reported by the Wildlife Incident Investigation Scheme, the report says badgers, grey squirrels and hedgehogs had significantly lower residues than foxes. For hedgehogs it reports residues detected in 55% of samples (6 of 11), which is a very small sample. The report notes that most grey squirrels (9 of 16) were below the limit of quantification, but that a few had very high residues. Numbers this small cannot support conclusions about the population as a whole.
Trends over time and what they do not prove
The report says summed SGAR residues have significantly increased over time in most species examined, and that residues and their occurrence rose significantly after the regulation change. It notes that the increase is largely driven by brodifacoum residues, whereas difenacoum residues in barn owls have recently shown a decreasing trend. Exposure has continued to increase in some species, such as the red kite and buzzard.
The authors stress that these changes are concurrent with the regulation change and the stewardship regime, not proven to be caused by either. They say the contrasting patterns among the active ingredients could result from changes in how much and for what purpose the products are used, or from other environmental factors such as diet. They recommend further work to identify the ecological factors that drive uptake and to integrate them into monitoring, and say further analysis is needed to understand the effect of the regulation change and the effectiveness of stewardship. In other words, the report identifies a pattern of concern and does not settle its cause.
What stewardship is
CRRU UK says it was set up in response to concern from government agencies that wildlife such as barn owls, kestrels and red kites were being accidentally exposed to rodenticides, and that those agencies called for better stewardship. Under its “Think Wildlife” banner it promotes best practice. Its home page summarises the stewardship rules: they apply to the supply and use of rodenticides authorised for application by professionals outdoors and carrying labels with stewardship conditions; pest controllers, farmers and gamekeepers must be qualified to access professional products; the rule is “no proof, no supply” of competence; and users should use rodenticides only after careful consideration of all options, using first the methods expected to be fully effective but presenting lower risks to wildlife. It adds that rodenticide residues in wildlife are being monitored closely and that HSE and other government agencies oversee stewardship, wildlife residues and rodenticide availability.
The site’s article on why professional rat poison access differs from what you can buy explains the access rules, and the article on feeding garden birds without feeding rats covers a way of reducing the rat problem at source.
What this means for a householder
The report does not test any product or household method. A customer can reasonably ask a pest controller how they minimise risks to wildlife, given that CRRU’s own wording says lower-risk methods should be used first.
Common questions
Does the report say rat poison is killing barn owls?
No. It measures residues in livers, not the cause of death, and it notes that sensitivity to the poisons varies between species.
Has stewardship reduced exposure?
The report says residues generally rose over time in most species after the 2015 changes, and that it cannot separate the effects of the regulation change from stewardship.
The bottom line
UKCEH’s 2025 report shows that UK predators and scavengers are widely exposed to second-generation rodenticides, with the highest residues in generalists and scavengers such as foxes and red kites, and that residues generally rose over time. It does not prove why. CRRU UK’s stewardship scheme says professionals should use lower-risk methods first, and monitoring continues.
Sources
- UK Centre for Ecology & Hydrology, “Second Generation Anticoagulant Rodenticides (SGARs) in Mammals and Predatory Birds: An interspecies comparison” (26 February 2025) (pbms.ceh.ac.uk)
- CRRU UK, “Think Wildlife” (stewardship essentials) (thinkwildlife.org)
- CRRU UK, “About CRRU UK” (thinkwildlife.org)