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Three Warblers in Catalonia Differed in Prey Choice, Prey Size and Use of Aquatic Prey

Common Reed Warbler perched on reeds at RSPB Saltholme
Research · Ecology

Three warblers breeding in reedbeds in Catalonia, Spain differed in the prey they ate, the size of those prey and how strongly their diets were linked to aquatic habitats. Researchers used DNA metabarcoding, which identifies prey from genetic traces in faeces, to compare Common Reed Warblers (Acrocephalus scirpaceus), Great Reed Warblers (Acrocephalus arundinaceus) and Cetti’s Warblers (Cettia cetti). The final diet dataset contained 189 samples: 137 from Common Reed Warblers and 26 from each of the other two species.

Common Reed Warblers had the highest share of aquatic prey

Aquatic prey taxa made up 37% of the prey taxa detected in Common Reed Warbler samples, compared with 17% in Cetti’s Warbler samples. Great Reed Warblers were intermediate at 29% and did not differ significantly from either species in this comparison. Chironomid midges were especially prominent in Common Reed Warbler diets, including several of their most frequently detected prey taxa.

Great Reed Warblers took larger prey

Prey taxa detected in Great Reed Warbler samples had an estimated mean body length of 16.1 mm, more than twice the 7.7 mm for Common Reed Warblers and 7.9 mm for Cetti’s Warblers. These lengths came from published body-size estimates for the identified prey taxa rather than direct measurements of prey in the faecal samples.

The three species also differed in dietary breadth. When the analysis focused on dominant prey taxa, Cetti’s Warblers had the broadest core diet, Common Reed Warblers were intermediate and Great Reed Warblers had the narrowest. Dietary overlap was greatest between Common and Great Reed Warblers and was higher than expected by chance, but the two species still differed in prey composition and prey size.

Several differences may help the species coexist

The authors conclude that the three warblers partition prey resources along several dimensions at once: prey taxonomy, prey size and the proportion of aquatic prey. Cetti’s Warblers, which use more terrestrial vegetation, had the most terrestrial diet, while the two Acrocephalus warblers overlapped more strongly in reedbed habitat and diet.

Study site also affected prey size and the proportion of aquatic prey, so the authors note that local prey communities and microhabitat use may contribute to the observed differences. Sample coverage was limited, particularly for Cetti’s Warblers, and fully describing dietary niche breadth would require more sampling. Even with those limits, the study found several complementary ways in which the three species separated their diets in Catalan reedbeds.

Sources and image credit

  1. Davies, S. R., Vaughan, I. P., Thomas, R. J., Josa, P., Bateman Posse, S., & Symondson, W. O. C. (2026). Dietary selectivity mediates niche overlap and interspecific competition in a reedbed warbler community in southern Europe. Ibis.Primary open-access research article first published 8 August 2026. Full text checked. DNA metabarcoding compared 189 diet samples from Common Reed, Great Reed and Cetti’s Warblers breeding in Catalonia and found dietary separation through prey taxonomy, prey size and aquatic versus terrestrial prey use.

Image: Wild Common Reed Warbler (Acrocephalus scirpaceus) perched on a reed at RSPB Saltholme, Hartlepool, United Kingdom, 12 June 2022. Photo: BLloydT / Wikimedia Commons. CC BY-SA 4.0. Representative image of one of the three study species; not a bird from the Catalan study. · CC BY-SA 4.0 · Source

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