Anticoagulant rodenticides in red kites (Milvus milvus) in Britain 2015

Walker, L.A. ORCID:; Jaffe, J.E.; Barnett, E.A.; Chaplow, J.S. ORCID:; Charman, S.; Giela, A.; Jones, A.; Pereira, M.G. ORCID:; Potter, E.D.; Sainsbury, A.W.; Sleep, D. ORCID:; Thompson, N.J.; Senior, C.; Sharp, E.A.; Shore, R.F.. 2017 Anticoagulant rodenticides in red kites (Milvus milvus) in Britain 2015. Lancaster, NERC/Centre for Ecology & Hydrology, 18pp. (CEH Project no. C05191)

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Second generation anticoagulant rodenticides (SGARs) can be toxic to all mammals and birds. Various studies have shown that, in Britain, there is widespread exposure to SGARs in a diverse range of predatory mammals and birds, including red kites (Milvus milvus) which scavenge dead rats, a target species for rodent control. The Wildlife Incident Monitoring Scheme (WIIS) and the Predatory Bird Monitoring Scheme (PBMS) have shown that some mortalities result from this secondary exposure. The aim of the current study was to assess the scale and severity of exposure to SGARs (as assessed from the presence of liver SGAR residues) in red kites found dead in Britain in 2015. Carcasses, typically found by members of the public, were submitted for examination and analysis either to the Institute of Zoology’s Disease Risk Analysis and Health Surveillance programme (DRAHS) or to the Centre for Ecology & Hydrology’s Predatory Bird Monitoring Scheme, partners in the WILDCOMS network. We also report the results of SGAR analysis of red kites from England, Wales and Scotland that died in 2015 and analysed by the WIIS, who are also partners of the WILDCOMS network. Eighteen red kites from England & Wales were necropsied by either the DRAHS or the PBMS and the livers of the birds were analysed for SGARs by the PBMS. All had detectable liver residues of difenacoum and brodifacoum, and most also contained detectable liver bromadiolone residues. Difethialone was less frequently detected and flocoumafen was not detected in any birds. The presence of detectable brodifacoum residues in all birds may partly reflect the predominance of adult birds in the 2015 sample but may also indicate a growing prevalence of exposure to this compound. The percentage of red kites found by the PBMS to contain brodifacoum has increased since 2010 although any influence of age on this trend has not yet been examined. Sum liver SGAR concentrations in the 18 kites ranged between 50 and 1266 ng/g wet wt. (arithmetic mean: 463 ng/g). Post-mortems indicated that 7 of the kites had internal hemorrhaging that was not associated with detectable trauma; these birds typically had elevated sum SGAR liver concentrations. On the basis of these two factors, it is considered probable that SGARs were a contributory cause of death in these birds. The exposure pattern observed in 8 red kites from England & Wales analysed by the WIIS was very similar to that observed in birds analysed by the PBMS, with detectable liver residues of difenacoum and brodifacoum in all birds and bromadiolone in most. SGARs were assessed to be a contributory cause of death in two birds. Thus, of the 26 red kites from England & Wales analysed overall, SGARs were considered to be implicated in the deaths of 9 (35%). Residue data were available through the WIIS for 6 red kites from Scotland that died in 2015. Three kites (50%) had liver residues of at least two SGARs (bromadiolone and difenacoum); brodifacoum was also detected in one of these kites. SGARs were assessed to be a contributory cause of death in the bird that had residues of three SGARs. The data, although sample size is small, suggest that exposure of kites to SGARs may have been less marked in Scotland than in England & Wales in 2015, as has been found for other species.

Item Type: Publication - Report
UKCEH and CEH Sections/Science Areas: Pollution (Science Area 2017-)
Funders/Sponsors: NERC/Centre for Ecology & Hydrology, Natural England, Campaign for Responsible Rodenticide Use
Additional Keywords: Predatory Bird Monitoring Scheme, Wildlife Incident Investigation Scheme, difenacoum, bromadiolone, brodifacoum, flocoumafen, difethialone, monitoring, United Kingdom (UK)
NORA Subject Terms: Ecology and Environment
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Date made live: 01 Nov 2017 12:47 +0 (UTC)

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