Anticoagulant rodenticides in predatory birds 2011: a Predatory Bird Monitoring Scheme (PBMS) report

Walker, L.A. ORCID: https://orcid.org/0000-0002-1471-7075; Chaplow, J.S. ORCID: https://orcid.org/0000-0002-8058-8697; Llewellyn, N.R.; Pereira, M.G. ORCID: https://orcid.org/0000-0003-3740-0019; Potter, E.D.; Sainsbury, A.W.; Shore, R.F.. 2013 Anticoagulant rodenticides in predatory birds 2011: a Predatory Bird Monitoring Scheme (PBMS) report. Lancaster, NERC/Centre for Ecology & Hydrology, 29pp. (CEH Project no. C04288)

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Abstract/Summary

The Predatory Bird Monitoring Scheme (PBMS; http://pbms.ceh.ac.uk/) is the umbrella project that encompasses the Centre for Ecology & Hydrology’s National Capability contaminant monitoring and surveillance work on avian predators. By monitoring sentinel vertebrate species, the PBMS aims to detect and quantify current and emerging chemical threats to the environment and in particular to vertebrate wildlife. Anticoagulant rodenticides, and in particular second generation anticoagulant rodenticides (SGARs), can be toxic to all mammals and birds. Predators that feed upon rodents are particularly likely to be exposed to these compounds. The PBMS, together with other studies, have shown that there is widespread exposure to SGARs of a diverse range of predators in Britain and that some mortalities occur as a result. This report summarises the PBMS monitoring for anticoagulant rodenticides in barn owls (Tyto alba), kestrel (Falco tinnunculus) and red kites (Milvus milvus) that were found dead in 2011 and presents long term trend analysis for barn owls. During this year’s analysis, a change to the analytical methods used by the PBMS was trialed where the use of matrix-matched standards was compared to solvent-matched standards. Matrix matched standards gave higher % recoveries for spiked samples and more repeatable results, and consequently resulted in reporting of higher liver SGAR concentrations in birds with detectable residues. It was concluded that matrix-matched standards provided a better analysis and would be used in this and future years analysis, but that a predicted solvent-matched equivalent SGAR residue would be calculated for use in time and spatial trend analysis that involved comparisons with data from previous years. This would eliminate biases that could otherwise be introduced into the analysis due to changes in analytical methodology. In birds that died in 2011, SGARs were detected in 84% of 58 barn owls analysed and the most prevalent compounds were difenacoum and bromadiolone. The majority of the residues were low and not diagnosed as directly causing mortality. The livers from 18 red kites were analysed in 2011. Most (94%) had detectable liver SGAR concentrations, again mainly difenacoum and bromadiolone, although brodifacoum was also detected in 78% of the birds. Six of the red kites analysed showed signs of haemorrhaging thought possibly to be associated with rodenticide poisoning. However, only two of these birds had relatively high sum SGAR liver concentrations (> 0.4 µg/g wet weight) and the contribution of SGARs, if any, to the death of the other four birds is uncertain. SGARs were detected in all 20 kestrel analysed. The most prevalent rodenticides detected in kestrel livers were difenacoum and bromadiolone. The co-occurrence of multiple residues was also prevalent with 19 out of 20 kestrels having more than one SGAR present in their liver. Due to a new collaborative arrangement with the Hawk Conservancy Trust the PBMS received a higher proportion of its barn owls and kestrels from the counties of Berkshire, Hampshire, Oxfordshire & Wilstshire. These counties are within a focus of rodenticide resistance in the Norway rat (Rattus norvegicus) and we tested whether there were significant differences for the prevalence and magnitude of SGAR residues in barn owls and kestrels between this area and other counties. There were no significant differences between either barn owls or kestrels from resistance and non-resistance counties in either the proportion of birds with detectable liver SGAR residues or the magnitude of liver SGAR concentrations in those birds with detected residues. However, the sample size examined was relatively small and it would be valuable in the future to conduct an analysis of the potential impact of resistance on residue prevalence and magnitude for birds collected over a longer time-scale and incorporating all counties where resistance to SGARs in rats has been documented. SGARs have been monitored in barn owls since 1983. Data on long-term trends have been adjusted to account for changes over time in sensitivity of analytical methods. This has meant that very low residues (<0.025 µg/g wet weight), which are now detectable, are not included in the time trend analysis. Overall, the proportion of barn owls with detectable liver concentrations of one or more SGAR has increased significantly over the course of monitoring. The highest value was recorded in 2008 while the value for 2011 was 25.9%. The proportion of barn owls with detectable SGAR residues over the period 1990-2011 was two-fold higher in England than in Scotland and Wales and also varied significantly between different regions of England. Between 1997 and 2011 there has not been any significant progressive increase or decrease in detectable SGAR residues in kestrels.

Item Type:	Publication - Report
Programmes:	CEH Topics & Objectives 2009 - 2012 > Biogeochemistry > BGC Topic 1 - Monitoring and Interpretation of Biogeochemical and Climate Changes > BGC - 1.1 - Monitor concentrations, fluxes, physico-chemical forms of current and emerging pollutants ...
UKCEH and CEH Sections/Science Areas:	Shore
Additional Pages:	Addendum
Funders/Sponsors:	NERC/Centre for Ecology & Hydrology, Natural England, Environment Agency, Campaign for Responsible Rodenticide Use, Royal Society for the Protection of Birds
Additional Information. Not used in RCUK Gateway to Research.:	Freely available online - Official URL link provides full text. Addendum also available separately from PBMS website.
Additional Keywords:	annual report, birds of prey, rodenticide, barn owl, kestrel, red kite, difenacoum, bromadiolone, brodifacoum, flocoumafen, difethialone, monitoring, United Kingdom (UK), PBMS
NORA Subject Terms:	Ecology and Environment Zoology
Related URLs:	Project Website
Date made live:	20 Feb 2013 14:51 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/500093

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