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Little Egrets, Glossy Ibises and Eurasian Spoonbills Declined in Danube Delta Colonies

Little egret flying across wetland habitat in the Danube Delta
Research · Ecology

A study of ten colonial waterbird species in the Romanian Danube Delta found downward trends in nine of them between 2016 and 2023. The clearest declines were in little egret (Egretta garzetta), glossy ibis (Plegadis falcinellus) and Eurasian spoonbill (Platalea leucorodia), while severe drought reduced aquatic foraging habitat around several colonies. The study was published on 26 January 2026 in Birds.

Researchers combined breeding-colony censuses from five sites in the Danube Delta Biosphere Reserve with satellite-derived measurements of surface water, local hydrological records and meteorological data. The census unit was an apparently occupied nest, identified from adults, eggs, chicks or fresh nesting signs and used to estimate breeding pairs. The abundance trends therefore describe breeding pairs in the monitored colonies, not all individuals present in the delta. Across all ten species, the colonies held an average of about 5,900 breeding pairs per year during the eight-year study. Across the waterbird community, colony numbers varied most strongly with spring temperatures and changes in water level. Little egret was among the species whose decline coincided with shrinking surface-water habitat.

Three species showed clear declines

Little egrets were among the dominant members of the colony community, accounting for about 12% of the cumulative abundance recorded across the study period. Glossy ibises accounted for 2.6% and Eurasian spoonbills for 0.6%. Despite these large differences in abundance, all three showed clear downward trends from 2016 to 2023.

Temporal trends in colonial waterbird abundance in the Danube Delta, including little egret
Temporal trends in the abundance of the ten colonial waterbird species monitored from 2016 to 2023. Little egret, glossy ibis and eurasian spoonbill (Platalea leucorodia) showed statistically significant declines. Figure 11 from Ion et al. (2026), Birds, CC BY 4.0.

Drought reduced water around colonies

The strongest changes in the wider waterbird community coincided with the severe drought period from 2020 to 2022. Several central colonies declined sharply or disappeared locally, while later increases in water levels allowed some recolonisation at lower densities than before the drought.

The amount of open water around colonies was closely related to the abundance of colonial waterbirds. Around the Nebunu colony, for example, the surface-water area within a five-kilometre buffer contracted by about 48% between 2019 and 2022, reducing nearby aquatic feeding habitat.

Persistent water became increasingly important

The authors identify little egret, glossy ibis and Eurasian spoonbill as particularly vulnerable to rapid contraction of aquatic habitat.

The study also recorded an eastward shift in parts of the breeding assemblage toward areas with more persistent water and better hydrological connectivity. The authors conclude that maintaining sufficient water around important colonies will be increasingly important as drought and hydrological variability alter the delta’s wetlands.

Sources and image credit

  1. Ion, C., Jitariu, V., Bolboacă, L. E., Ichim, P., Marinov, M., Alexe, V., & Doroșencu, A. (2026). Environmental Drivers of Waterbird Colonies’ Dynamic in the Danube Delta Biosphere Reserve Under the Context of Climate and Hydrological Change. Birds, 7(1), 6. https://doi.org/10.3390/birds7010006Primary peer-reviewed open-access article published 26 January 2026. Colony censuses from 2016–2023 were integrated with remote sensing, hydrology and meteorological data. Little egret accounted for 12.01% of cumulative abundance and showed a statistically significant downward trend; Eurasian spoonbill and glossy ibis were the other two species with significant declines. Surface water around the Nebunu colony contracted by about 48% between 2019 and 2022.

Image: Diego Delso — wild little egret (Egretta garzetta) photographed in the Romanian Danube Delta on 28 May 2016; the same wetland system examined in the study. Source: Wikimedia Commons. · CC BY-SA 4.0 · 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

Little Egret Egretta garzetta Explore species Eurasian Spoonbill Platalea leucorodia Explore species

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