Autopsy on a barn owl

Second generation anticoagulant rodenticides (SGARs) are used to control commensal rodents (rats and mice) throughout the world. However, wildlife species are also exposed to these poisons, both through consuming bait and by eating poisoned rodents.

Concerns in the UK about effects on wildlife have resulted in stewardship for anticoagulant rodenticides. This is led by an industry consortium, the Campaign for Responsible Use (CRRU) UK. The aim is to change user behaviour so that unintentional wildlife exposure is reduced. 

Changes in wildlife exposure are assessed by measuring liver SGAR residues in the barn owl, a sentinel rodent-feeding species. Residue levels are compared with those in a pre-stewardship "baseline" period (2006-2012). Measurements are made on carcasses submitted to the Predatory Bird Monitoring Scheme (PBMS); most of the owls have died from starvation or in traffic collisions.

The Centre for Ecology & Hydrology (CEH) has now published its report of SGAR residues in barn owls that died in 2016, the year that stewardship was introduced.

The main findings were:

  • no significant change from "baseline" years in most indicators of SGAR exposure, although there was a decline in low level difenacoum residues
  • the most frequently detected SGARs in barn owls in 2016 were bromadiolone, difenacoum and brodifacoum, as in the 2006-2012 "baseline years"
  • overall in 2016, 78% of owls had liver residues of at least one SGAR, similar to "baseline years" but lower than in 2015

Lee Walker, coordinator for the PBMS, said, "The results for 2016 are generally consistent with the baseline years. Given stewardship was launched only part way through the year, it is probably too early to expect changes from baseline levels in liver SGARs in 2016.  If stewardship is successful, we expect to see reductions in liver SGAR concentrations in barn owls in future years."

The monitoring of SGARs in barn owls is conducted independently by CEH. It is funded by CRRU UK, who recently announced the publication of CEH’s report. All activities conducted under the stewardship scheme are reviewed by a government oversight group led by the Health and Safety Executive.

Additional information

The Predatory Bird Monitoring Scheme (PBMS) is a long-term, national monitoring scheme whose aim is to detect and quantify current and emerging chemical threats to the environment.

The PBMS relies on members of the public to send in deceased birds of prey - here's what to do

Staff page of Lee Walker, Centre for Ecology & Hydrology

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