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Anurans Were the Main Assimilated Food Source for Cattle Egret Chicks in Southern Brazil

Western cattle egret feeding a chick on a branch in Portugal
Research · Ecology

A study of a mixed heron colony in southern Brazil found that western cattle egret (Ardea ibis) chicks relied strongly on terrestrial food, with anurans — frogs and toads — emerging as their main assimilated food source. The study was published on 26 February 2026 in Hydrobiologia and compared western cattle egret with snowy egret (Egretta thula) and black-crowned night heron (Nycticorax nycticorax) breeding together in the Lagoa dos Patos estuary.

The researchers combined two complementary approaches. Food remains from regurgitates and pellets showed which prey had been eaten, while carbon and nitrogen stable isotopes in chick blood provided information about food sources that had been assimilated into the birds’ tissues over a longer period. Sampling took place in a breeding colony on Marinheiros Island in Rio Grande do Sul.

Anurans supplied 52.1% of reconstructed prey mass

Food remains from western cattle egrets contained mainly insects, spiders and anurans. Insects occurred in all analysed samples and were the most important prey group by a combined diet index. When prey were reconstructed by mass, however, anurans contributed 52.1% and insects 27.4% of the cattle egret diet.

Stable isotopes also identified anurans as the main assimilated food source

The stable-isotope models supported the importance of amphibian prey. Anurans were estimated to be the main assimilated food source for western cattle egret chicks, followed by terrestrial insects. Snowy egret food remains were dominated by aquatic prey, while the isotope model indicated substantial contributions from both anurans and aquatic insects. Black-crowned night herons had the broadest and most generalist isotopic niche and used food from several aquatic and terrestrial sources.

Estimated contributions of anurans, fish, aquatic insects, terrestrial insects and crustaceans to the diets of cattle egret, black-crowned night heron and snowy egret chicks
Estimated contributions of potential prey sources to chick blood in the three heron species. Figure 3 from Travessas et al. (2026), Hydrobiologia, CC BY 4.0.

The three species still shared some resources. The isotopic niche of western cattle egret overlapped by 73.8% with that of black-crowned night heron, but by only 17% with snowy egret. The researchers therefore found both overlap and clear differences in how the three species used available food resources.

The authors conclude that the species can breed together in the same colony because they separate their ecological niches in at least one important dimension. Differences in prey, feeding habitat and time of foraging allow the birds to share some food resources without using the environment in exactly the same way.

Sources and image credit

  1. Travessas, A. O., Barreto, C. T., Fernandez, C. N., Chaves, D. C., & Bugoni, L. (2026). Diet and resource partitioning between egrets and herons in an estuarine colony in southern Brazil. Hydrobiologia, 853(11), 3303–3319. https://doi.org/10.1007/s10750-026-06144-9Primary peer-reviewed open-access article, first published 26 February 2026 under CC BY 4.0. Food-remains and stable-isotope analyses from a mixed heron colony at Lagoa dos Patos showed a mainly terrestrial diet in western cattle egrets; anurans were their main assimilated food source, followed by terrestrial insects.

Image: Luiz Lapa / Wikimedia Commons — western cattle egret (Ardea ibis) feeding a chick at Rio-a-Dentro, Escaroupim, Salvaterra de Magos, Santarém, Portugal, photographed 27 June 2024; illustrative photograph, not from the southern Brazil study · CC BY 2.0 — https://creativecommons.org/licenses/by/2.0/ · 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

Ecology

SPECIES IN THIS STORY

Species in this story

Western Cattle Egret Ardea ibis Explore species Snowy Egret Egretta thula Explore species Black-crowned Night Heron Nycticorax nycticorax Explore species

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