Second generation anticoagulant rodenticide residues in barn owls 2020

Walker, Lee A. ORCID: https://orcid.org/0000-0002-1471-7075; Chaplow, Jacky S. ORCID: https://orcid.org/0000-0002-8058-8697; Dodd, Beverley A.; Potter, Elaine D.; Pereira, M. Gloria ORCID: https://orcid.org/0000-0003-3740-0019; Sleep, Darren ORCID: https://orcid.org/0009-0002-1128-1883; Hunt, Alexander G.. 2022 Second generation anticoagulant rodenticide residues in barn owls 2020. Lancaster, UK Centre for Ecology & Hydrology, 23pp. (UKCEH Project no. 05766) (Unpublished)

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Abstract/Summary

The current report is the sixth in a series of annual reports that describe the monitoring of second generation anticoagulant rodenticide (SGAR) liver residues in barn owls Tyto alba in Britain. This work is an element of an overarching monitoring programme undertaken to track the outcomes of stewardship activities associated with the use of anticoagulant rodenticides. The barn owl is used for exposure monitoring as it is considered a sentinel for species that are generalist predators of small mammals in rural areas. The specific work reported here is the measurement of liver SGAR residues in 100 barn owls that died in 2020 at locations across Britain. The residue data are compared with those from 395 barn owls that died between 2006 and 2012 (hereafter termed baseline years), prior to changes in anticoagulant rodenticide (AR) authorisations and onset of stewardship. As in the baseline years, the compounds detected most frequently in barn owls that died in 2020 were brodifacoum, bromadiolone, and difenacoum. Overall, 88% of the owls had detectable liver residues of one or more SGAR. Numbers of barn owls containing detectable residues of flocoumafen and difethialone. There was no significant difference in the proportion of barn owls with detectable liver residues of flocoumafen between the baseline years and 2020. There was a significantly higher proportion of barn owls with detectable liver residues of difethialone in 2020 compared to baseline years (5% vs 0.3%) but it was lower than in some of the intervening years (2016-2019). The ratio of birds with “low” (<100 ng/g wet weight (wet wt.) vs “high” (>100 ng/g wet wt.) concentrations for any single SGAR or for ∑SGARs. There were significantly higher proportion of birds from 2020 with “high” concentrations of brodifacoum and summed SGARs (ƩSGARs) detected in their livers compared to baseline years. Average concentrations of brodifacoum, difenacoum, bromadiolone and ∑SGARs in the cohort of owls with “low” residues (<100 ng/g wet wt.) and “high” residues (>100 ng/g wet wt.). There was no significant difference between barn owls from baseline years and from 2020 in the concentrations of either “low” or “high” residues for all residues summed (∑SGARs), bromadiolone and difenacoum, or “high” brodifacoum residues. The median concentration of “low” brodifacoum residues was higher in birds from 2020 than in baseline years. Overall, there were few differences in liver SGAR accumulation between barn owls that died in baseline years and in 2020, the eception being a potential increase brodifacoum residues. The lack of significant reductions in SGAR residues in barn owls in 2020 suggests that full implementation of stewardship since 2018 has yet to result in a statistically significant reduction in exposure of barn owls to SGARs.

Item Type:	Publication - Report (Project Report)
UKCEH and CEH Sections/Science Areas:	Pollution (Science Area 2017-) Water Resources (Science Area 2017-)
Funders/Sponsors:	Campaign for Responsible Rodenticide Use, Natural Environment Research Council
NORA Subject Terms:	Earth Sciences Ecology and Environment Zoology
Date made live:	23 Sep 2022 16:51 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/533263

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