Second generation anticoagulant rodenticide residues in red kites 2021

Ozaki, Shinji ORCID: https://orcid.org/0000-0002-4243-8479; Barnett, E.A.; Chaplow, J.S. ORCID: https://orcid.org/0000-0002-8058-8697; Charman, S.; Flynn, E.; Galloway, M.; Melton, L.; Mocogni, L.A.; Pereira, M.G. ORCID: https://orcid.org/0000-0003-3740-0019; Potter, E.D.; Sainsbury, A.W.; Shadbolt, T.; Sleep, D. ORCID: https://orcid.org/0009-0002-1128-1883; Sharp, E.A.; Toon, B.; Walker, Lee ORCID: https://orcid.org/0000-0002-1471-7075. 2024 Second generation anticoagulant rodenticide residues in red kites 2021. Lancaster, UK Centre for Ecology & Hydology, 34pp.

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Abstract/Summary

Second-generation anticoagulant rodenticides (SGARs) can be toxic to all mammals and birds if consumed. 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 Investigation Scheme (WIIS) and the Predatory Bird Monitoring Scheme (PBMS) have shown that some mortalities result from this secondary exposure. In the present study, we analysed liver SGAR residues in 42 red kites that had been found dead in Britain in 2021. The carcasses were submitted to and necropsied by the Disease Risk Analysis and Health Surveillance (DRAHS) programme, the PBMS, the WIIS for England & Wales, the WIIS for Scotland and the Raptor Health Scotland study. All the organisations are partners in the WILDCOMS (Wildlife Disease & Contaminant Monitoring & Surveillance Network) network that promotes collaboration among surveillance schemes that monitor disease and contaminants in vertebrate wildlife in the UK. The UK Rodenticide Stewardship Regime (hereafter referred to as the stewardship scheme) began to come into force in mid-2016 as re-registration of products for use in the UK was approved by the HSE; full implementation of the scheme was in early 2018. The key aim of this stewardship initiative is to support competence among all users of professional SGAR products. A potential benefit of this may be the reduced exposure of non-target wildlife to anticoagulant rodenticides. However, the number and density of SGAR-contaminated rats may remain unchanged although diligent searching, removal, and safe disposal of poisoned rats, as promoted by the stewardship regime, might be expected to reduce the availability of poisoned dead rats to red kites (and other scavengers) and thereby reduce the proportion of birds that are exposed and/or the magnitude of exposure. Concomitant with the stewardship scheme was a relaxation of the indoor-use-only-restriction applied to brodifacoum, flocoumafen, and difethialone, the three most acutely toxic SGARs to use indoor and outdoor around buildings. Any consequent increase in outdoor use of these three SGARs could increase the risk of secondary exposure in red kites. We therefore compared the data in the current report with that collected in 2015 and 2016 to determine if there was any evidence of a change in pattern or magnitude of exposure in red kites that might be connected to stewardship and/or change in usage restriction. All of the 39 red kites from England & Wales and two of the three red kites from Scotland had detectable liver residues of at least one type of SGAR. When considering the sample of red kites as a whole, brodifacoum, difenacoum, and bromadiolone were each detected in 41, 39, and 32 red kites, respectively. Difethialone was found in four individuals, while flocoumafen was detected in no bird. The proportion of analysed red kites exposed to SGARs in 2015 (91%), 2016 (90%), 2017 (96%), 2018 (100%), 2019 (91%), 2020 (88%), and 2021 (98%) was similar at circa 88% or more. Difenacoum, brodifacoum, and bromadiolone were the most prevalent compounds (detected in 87%, 87%, and 76% of red kites across the seven years for each compound, respectively). On average, there were detectable residues of three different SGARs in each red kite liver likely demonstrating multiple exposures. Sum liver SGAR concentrations in birds from 2021 ranged between non-detectable and 3223.7 ng/g wet weight (arithmetic mean: 482 ng/g wet weight, median 334.4 ng/g wet weight). Necropsy examinations indicated that five red kites showed signs of being poisoned by SGARs (i.e., showing internal haemorrhaging that is not associated with detectable trauma and also having detectable liver SGAR concentrations). These samples accounted for 14% of the red kites of this year excluding uncertain poisoning cases. These five birds had sum SGAR liver concentrations of 463.5, 684, 990, 1405.9, and 3223.7 ng/g wet weight. SGARs were considered a contributory cause of death resulting from unspecified use in these cases. SGARs were a contributory cause of death in 16% of the red kite cases examined across all seven years. Over the period 2015 to 2021, a reduction has been observed in the percentage of red kites examined that were diagnosed as birds in which SGARs were implicated as a contributory cause of death. However, given that the WIIS scheme specifically examines suspected poisoning incidents, it is likely that poisoned birds are over represented in this sample compared to the population as a whole in all seven years. Due to these reasons, caution should be used when interpreting evident changes in mortality rates due to the sampling protocols used in this study that may lead to over reporting of mortality rates, and those rates being subject to variations in relative contribution of the WIIS and PBMS to each year’s sample. There were statistically significant differences between years in median summed SGAR residues, irrespective of cause of death. The magnitude of accumulated summed SGAR residues, particularly sum of brodifacoum, flocoumafen, and difethialone concentrations, was significantly higher in 2021 than in many of the previous years. Given low occurrence and low concentrations of flocoumafen and difethialone residues, it is likely that the magnitude of brodifacoum residues has increased over recent years. Data on presence/absence of detectable brodifacoum, flocoumafen or difethialone residues were compared for 2015/2016 and 2017/18/19/20/21. The proportion of red kites with detectable residues of these three SGARs was not significantly different between in 2015/2016 (82%) and in 2017/18/19/20/21 (88%). Similarly, there was no significant difference in the proportion of red kites with detectable liver difenacoum or bromadiolone residues (90% in 2015/2016 vs. 94% in 2017/18/19/20/21). Since the implementation of the stewardship regime, no difference in exposure pattern relating to active ingredient has been detected with the exception of an increase in the concentrations of brodifacoum. Spatial analysis, by county/region indicated that across the monitoring period highest exposure to SGARs in red kites appeared to be around the Berkshire/Hampshire and, to a lesser extent, North Yorkshire. Our findings do not indicate that there has been a broad scale change in exposure in red kites to SGARs following implementation of stewardship in terms of either the proportion of the sample exposed or the magnitude of sum SGARs residues detected. However, there is evidence that the proportion of red kites in which SGARs were implicated as a contributory mortality factor has decreased in more recent years. Alternative approaches to monitoring SGARs in red kites could be considered that analyses a random but representative sample, and as part of such a programme there may also be value in monitoring SGARs in the blood of tracked individuals. There was no clear evidence that relaxation of usage restrictions on brodifacoum, difethialone and flocoumafen has altered the pattern of residues for these compounds in red kites to date, when considered collectively but brodifacoum exposure has increased in recent years

Item Type:	Publication - Report (Project Report)
UKCEH and CEH Sections/Science Areas:	Pollution (Science Area 2017-)
Funders/Sponsors:	Natural England, Natural Environment Research Council, Campaign for Responsible Rodenticide Use
NORA Subject Terms:	Ecology and Environment
Related URLs:	Project Website
Date made live:	03 Jun 2024 10:41 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/537504

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