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Anticoagulant rodenticides in predatory birds 2009: a Predatory Bird Monitoring Scheme (PBMS) report.

By L.A. Walker, N.R. Llewellyn, M.G. Pereira, E.D. Potter, A.W. Sainsbury and R.F. Shore


The Predatory Bird Monitoring Scheme (PBMS; 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.\ud 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), and red kites (Milvus milvus) that were found dead in 2009 and presents long term trend analysis for barn owls.\ud Since 2006, anticoagulant rodenticide concentrations have been quantified using the more sensitive Liquid Chromatography – Mass Spectrometry (LC-MS) method. This has resulted in lower concentrations of these compounds being detected than was previously possible. Consequently, for samples from 2006 onwards, the proportion of birds in which anticoagulant rodenticides have been detected has increased compared to previous years.\ud SGARs were detected in 89% of barn owls and the most prevalent compounds were difenacoum and bromadiolone. The majority of the residues were low and not diagnosed as directly causing mortality. Only five red kites were received by the scheme in 2009. Most of the red kites (4 o/5 birds) had detectable liver SGAR concentrations, again mainly difenacoum and bromadiolone although brodifacoum was also detected in over half the birds. Two of the five red kites analysed showed signs of haemorrhaging thought possibly to be associated with rodenticide poisoning.\ud 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 (<0.025µg/g wet weight), which are now easily detectable, are not included in the time trend analysis. The proportion of owls with detectable SGAR residues was found to be two-fold higher in England than in either Scotland or Wales. 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 but this was approximately twice that for the previous three years. The value for 2009 was lower than 2008 but remains one of the highest recorded since monitoring began. \ud Continued monitoring is required to determine whether the high detection rate for SGARs in barn owls in 2008 and 2009 will change. Although our data for red kites in 2009 is limited, it is consistent with a high proportion of red kites being exposed to SGARs and some dying as a result. This species remains at particular risk from anticoagulant rodenticides.\u

Topics: Ecology and Environment
Publisher: NERC/Centre for Ecology & Hydrology
Year: 2010
OAI identifier:

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