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Ground Beetles Dominated the Diet of Eurasian Tree Sparrow Chicks

Eurasian tree sparrow fledgling
Research · Ecology

Ground beetles dominated the invertebrate diet detected in Eurasian tree sparrow (Passer montanus) chicks at three sites on the Marlborough Downs in southern England. The 2026 study was the first molecular analysis of nestling diet in the species and pointed to predominantly ground-based foraging by the adults feeding them.

During the 2024 breeding season, researchers collected faecal samples from chicks and used DNA metabarcoding of the COI region to identify prey. This method reads short DNA sequences from the mixed remains in a sample and compares them with reference sequences, allowing several prey species to be identified at once; COI is a commonly used animal DNA-barcode region. Usable invertebrate DNA was recovered from 59 samples. The analysis detected 22 species from five orders: beetles, flies, wasps and their relatives, true bugs and spiders.

Ground beetles were the most frequent individual prey

Beetles were detected in 73.1% of the samples. The two most frequently identified individual prey species were both ground beetles: Pterostichus melanarius occurred in 22.6% of samples and Poecilus cupreus in 12.9%.

Relatively few invertebrate species were detected in each sample. The authors suggest two possible explanations: parents may have repeatedly delivered the same prey species, or food may pass through young chicks quickly enough for each sample to represent only a short dietary window.

Diet varied between sites, habitats and sampling times

Prey composition showed significant spatial and temporal variation across the study. The authors link this pattern to local habitat features and cropping patterns around nest sites, which can change which invertebrates are available to breeding tree sparrows.

The prominence of ground beetles led the authors to conclude that parents were foraging mainly at or close to ground level. They therefore highlight bare ground and sparse or short vegetation as potentially important feeding habitat during the breeding season. The study therefore provides a molecular baseline for examining how chick diet varies between habitats and through the breeding season.

Sources and image credit

  1. Baker et al. (2026). Baseline spatiotemporal patterns in the invertebrate diet of Tree Sparrow (Passer montanus) chicks revealed using DNA metabarcoding. Bird Study, in press.Primary institutional repository record for the accepted Bird Study manuscript, deposited 4 August 2026. The accepted full text remains under publisher embargo, but the repository abstract reports the study design and main results: 59 chick faecal samples from three Marlborough Downs sites in 2024 yielded 22 invertebrate species; Coleoptera occurred in 73.11% of samples, with Pterostichus melanarius and Poecilus cupreus the most frequent individual prey. The authors conclude that parental foraging was predominantly ground-based and highlight bare ground and sparse or short vegetation during breeding.

Image: Aomorikuma — Eurasian tree sparrow (Passer montanus) fledgling, photographed 3 July 2008; Wikimedia Commons, CC BY-SA 3.0. Representative species image; not one of the chicks sampled in the Marlborough Downs study. · CC BY-SA 3.0 · Source

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