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Common Kestrel Pellets Had Much Higher Microplastic Concentrations Than Barn Owl Pellets in Hampshire

Common kestrel in Hampshire, England
Research · Ecology

A study of regurgitated pellets from common kestrels (Falco tinnunculus) and barn owls (Tyto alba) in Hampshire, England, found microplastics in most samples from both species, but at markedly different concentrations. Researchers collected 24 pellets from each species at paired nest sites in August 2024 and identified particles using Fourier-transform infrared spectroscopy (FTIR), which distinguishes plastic polymers from their characteristic absorption of infrared light.

Microplastics were detected in 22 of 24 kestrel pellets, or 92%, and 20 of 24 barn owl pellets, or 83%. Median density was significantly higher in kestrel pellets at 18.46 particles per gram of dry pellet, compared with 0.42 particles per gram in barn owl pellets. Thirteen polymer types were identified across the samples, and the most numerous particles in both species were in the 25–50 μm size class.

Figure comparing median microplastic concentrations in common kestrel and barn owl pellets
Median microplastic concentrations in barn owl and common kestrel pellets from Hampshire. Figure 1 from Ozturk et al. (2026), CC BY 4.0.

The two raptors use overlapping farmland and grassland habitats and both feed heavily on small mammals, but the authors found clear differences in the polymer profiles of their pellets. They suggest that variation in prey, foraging location and digestion could contribute to the species difference, while noting that their study did not analyse the diet of each pellet directly. They also caution that the much larger mass of barn owl pellets can dilute particle counts per gram. To check how much this affected the comparison, they estimated the total particles in an average pellet: about 17.0 for kestrel and 3.8 for barn owl. The difference therefore remained even without expressing the result per gram, although it was less extreme.

The pellets provide a non-invasive measure of dietary microplastic exposure, not a measure of plastic retained inside the birds. The authors explicitly note that pellets contain egested material and therefore cannot be used to estimate the quantity of microplastics remaining in body tissues.

Sources and image credit

  1. Ozturk, R., Adediran, G. A., Brass, D. P., Mills, W. F., Stevens, M., Robinson, A., & Black, S. (2026). Interspecific differences in microplastic accumulation and polymer profiles from regurgitated pellets of coexisting raptors. Environmental Pollution, 405, 128483. https://doi.org/10.1016/j.envpol.2026.128483Primary open-access research article available online 2 June 2026 under CC BY 4.0. Twenty-four pellets from common kestrels and 24 from barn owls were collected in Hampshire; 92% and 83% respectively contained microplastics, with significantly higher median particle density in kestrel pellets.

Image: Andy Morffew / Wikimedia Commons / Flickr — common kestrel in Hampshire, England, photographed 2 April 2021; representative image from the same county, not an identified sampled bird; cropped to 16:9 · CC BY 2.0 — https://creativecommons.org/licenses/by/2.0/ · Source

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