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Common Buzzards Had a Lower Modelled Threshold for Rodenticide Poisoning Than Red Kites

Common buzzard in flight
Conservation · Threats

A British study of second-generation anticoagulant rodenticides found widespread exposure in common buzzards (Buteo buteo) and red kites (Milvus milvus). At least one of the five analysed rodenticides was detected in 88.7% of 159 buzzards and 94.3% of 263 red kites examined after death.

The study, published online on 24 January 2026 in Environment International, used carcasses collected through wildlife monitoring and veterinary surveillance schemes. The buzzards came from England between 2009 and 2021, while the red kites were collected across Great Britain between 2015 and 2022.

Poisoned birds had much higher liver residues

Post-mortem evidence was used to distinguish deaths attributed to anticoagulant poisoning from other causes; residue concentration alone was not used to diagnose poisoning. Twenty-three buzzards, or 14.5% of the sample, and 42 red kites, or 16.0%, were classified as having been lethally poisoned.

Buzzards reached the 1% risk threshold at lower residues

The researchers linked summed liver residues to the probability of lethal poisoning and used a 1% probability as their conservation benchmark. This corresponded to 38.2 ng/g wet liver weight in common buzzards and 54.2 ng/g in red kites, rounded to suggested thresholds of about 40 and 55 ng/g.

Graphical abstract summarising rodenticide toxicity thresholds for common buzzards and red kites
The study’s graphical abstract summarises the field-derived toxicity thresholds for common buzzards and red kites. Ozaki et al. (2026), Environment International, CC BY 4.0. Source.

The species difference is biologically important. Red kites had higher overall exposure to second-generation anticoagulant rodenticides (SGARs) than common buzzards, yet the lower modelled thresholds in buzzards indicate greater susceptibility to lethal effects at a given summed liver residue. The authors argue that this balance between exposure and susceptibility helps explain why the proportion of carcasses classified as lethally poisoned was fairly similar in the two species.

These values are lower than the 100–200 ng/g concentrations that have often been used as conventional reference thresholds for predatory birds. The authors therefore argue that species-specific field data can reveal meaningful differences in susceptibility that broader reference values may miss.

The thresholds are for risk assessment, not diagnosis of individual birds

The authors emphasise that the model contains uncertainties and that anticoagulant poisoning in an individual bird cannot be diagnosed from liver concentration alone. Their proposed values are intended as probabilistic thresholds for assessing population-level risk from exposure to second-generation anticoagulant rodenticides.

Buzzards and red kites can be exposed when they eat rodents or other animals carrying anticoagulant residues. By deriving species-specific thresholds from large sets of free-living birds rather than relying only on laboratory reference values, the study provides a new tool for monitoring and managing the risk of secondary poisoning in British raptors.

Sources and image credit

  1. Ozaki, S., Barnett, E. A., Carter, H., Chaplow, J. S., Charman, S., Galloway, M., Pereira, M. G., Potter, E., Sainsbury, A. W., Shadbolt, T., Sharp, E. A., Shaw, G., Sleep, D., Walker, L. A., & Qassim, S. M. (2026). Probabilistic approach reveals the toxicity threshold values of free-living raptors in Great Britain, United Kingdom, for the lethal effect of second-generation anticoagulant rodenticides. Environment International, 208, 110099. https://doi.org/10.1016/j.envint.2026.110099Primary peer-reviewed open-access study, published online 24 January 2026.

Image: Olga Havlíčková / Wikimedia Commons — common buzzard (Buteo buteo), an unusually pale individual, in flight in the Czech Republic, 28 December 2022. Illustrative photograph, not a bird from the study. · CC BY-SA 4.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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