Programmes to reintroduce predatory birds are resource intensive and expensive, yet there are few long-term studies on the health of these reintroduced birds following release. A total of 326 red kites (Milvus milvus) were released at four sites in England between 1989 and 2006 as part of efforts to reintroduce this species to England and Scotland, resulting in the establishment of several rapidly expanding populations in the wild. Detailed post-mortem examinations were carried out on 162 individuals found dead between 1989 and 2007, involving both released and wild-fledged birds. Toxicological analysis of one or more compounds was performed on 110 of the 162 birds. Poisoning was diagnosed in 32 of these 110 kites, 19 from second-generation anticoagulant rodenticides, 9 from other pesticides and 6 from lead. Criteria for diagnosing anticoagulant rodenticide poisoning included visible haemorrhage on gross post-mortem examination and levels of anticoagulant rodenticide exceeding 100 ng/g, but levels were elevated above 100 ng/g in a further eight red kites without visible haemorrhages, suggesting poisoning may have occurred in more birds. The anticoagulant rodenticides difenacoum and bromadiolone were the most common vertebrate control agents involved during this period. Poisoning of red kites may be slowing their rate of population recovery and range expansion in England. Simple modifications of human activity, such as best practice in rodent control campaigns, tackling the illegal use of pesticides and the use of non-toxic alternatives to lead ammunition, can reduce our impact on red kites and probably other populations of predatory and scavenging species.
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The authors thank the following for their contributions to this study: James Kirkwood for initiating the study of disease in reintroduced red kites, Keith Bowey, Derek Holman, the late Peter Newbery, Helen Olive, Doug Simpson, Nigel Snell and Peter Stevens for collecting and submitting red kite carcasses, Jonathan Cracknell, Andrew Cunningham, Yedra Feltrer, Edmund Flach, Tracy Howard, Iain McGill, Romain Pizzi and Ann Pocknell for carrying out post-mortem examinations, Belinda Clark for pathological support, Shinto Kunjamma John and Shaheed Karl Macgregor for microbiological support, Ilona Furrokh, Gillian Ahearne, Christine Dean, Judith Howlett, Tony Fitzgerald, Joanne Korn, Janet Markham and Matthew Rendle for the care of hospitalised red kites, the analytical chemistry team in the Wildlife Incident Unit at Fera (lead by Ainsley Jones, Andrew Charlton and Sheonaidh Charman), Becki Lawson for scientific input into this paper and all the members of the public that have reported red kite carcasses.
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Molenaar, F.M., Jaffe, J.E., Carter, I. et al. Poisoning of reintroduced red kites (Milvus Milvus) in England. Eur J Wildl Res 63, 94 (2017). https://doi.org/10.1007/s10344-017-1152-z
- Birds of prey
- Anticoagulant rodenticide