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DNA Analysis Found Traces of 71 Species in Lesser Black-backed Gull Diet Samples

Lesser black-backed gull standing on a beach
Research · Ecology

A DNA metabarcoding study of lesser black-backed gull (Larus fuscus) diet detected 71 species across 61 genera in samples from chicks and adults in northwest England. The work was posted as a bioRxiv preprint on 20 July 2026 and has not yet been peer reviewed.

The researchers tested how well DNA metabarcoding can describe the highly varied diet of a generalist predator. DNA metabarcoding reads standard genetic markers from mixed biological material and matches the sequences to reference databases, allowing many food taxa to be identified from the same sample. They collected faecal and regurgitated material from pre-fledging chicks at two breeding colonies, one coastal and one inland, together with pharyngeal, stomach, intestinal and cloacal swabs from adult gull carcasses.

Different sample types gave different results

The samples were analysed with two genetic markers. COI was used to target animal DNA, while 12S focused on vertebrate DNA. The researchers also developed three blocking primers — short DNA sequences used to suppress copying of the gulls’ own DNA — so that food DNA would be easier to detect in the 12S analyses.

Without these blocking primers, useful dietary information was recovered from regurgitated and stomach samples, but not from intestinal or faecal samples. Adding blocking primers improved recovery of dietary DNA from faeces. At the same time, it increased amplification of contaminants and therefore raised the risk of false-positive detections.

This methodological difference was important because the preprint was designed not only to catalogue diet, but also to evaluate which samples and laboratory approaches are most informative when studying a species with a very broad diet.

Seventy-one species were detected

Across all sample types, the analyses identified 71 species belonging to 61 genera. The detections included earthworms, small mammals, commercial and non-commercial fish, northern lapwing (Vanellus vanellus) and livestock-derived food associated with urban environments.

The dietary profiles formed distinct groups associated with urban, agricultural and marine foraging. They also differed between age groups and between the two breeding colonies, indicating that lesser black-backed gulls in the study did not all use the same mixture of food resources.

A molecular view of a highly generalist diet

The authors conclude that DNA metabarcoding can reveal substantial dietary diversity and differences in resource use among colonies and age groups. They also show that the method is sensitive to both sample type and primer choice, particularly when faecal material is used.

Because blocking primers increased both dietary DNA recovery and contaminant amplification, the 71 detected species should be understood as metabarcoding detections produced through the study’s filtering and analytical workflow, rather than simply as a count of 71 directly observed prey items. The preprint presents the approach as a way to improve understanding of how dietary differences may relate to survival, reproduction and population change in gulls.

Sources and image credit

  1. Risely et al. (2026) — Evaluating DNA metabarcoding to characterise diet diversity and foraging strategies in a generalist mesopredator, the lesser black-backed gull (Larus fuscus)Primary preprint posted 20 July 2026 and still identified as a preprint during this review. The authors compared COI and vertebrate-targeted 12S metabarcoding across faecal and regurgitate samples from pre-fledging chicks at two breeding colonies in northwest England and swabs from adult gull carcasses. Blocking primers improved dietary DNA recovery from faeces but also increased contaminant amplification. Across all sample types, 71 unique species from 61 genera were detected, with dietary profiles differing among colonies and age cohorts.

Image: Hobbyfotowiki / Wikimedia Commons — adult Lesser Black-backed Gull (Larus fuscus) photographed on Heligoland, Germany, 12 May 2019. CC0 1.0. Representative species image; not a bird or scene from the northwest England diet study. · CC0 1.0 · Source

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