Multi-Scale Environmental Drivers of Heron and Egret Colony Assemblages in Korea Using Self-Organizing Map Clustering

Context Colonial herons and egrets breed within highly heterogeneous landscapes where environmental conditions vary across multiple spatial scales. Although landscape structure is expected to shape colony-level species assemblages, explicit multi-scale empirical assessments remain scarce, particularly at national extents. Objectives We sought to (1) identify emergent species-assemblage types among heron and egret colonies across South Korea, (2) determine how these assemblages correspond to landscape heterogeneity across nested spatial scales, and (3) quantify the scale-dependent importance of environmental predictors influencing colony identity. Methods We compiled species-specific nest counts from 176 breeding colonies and applied Self-Organizing Maps (SOM) to classify colony assemblages. Landscape variables were extracted from ESA CCI Plant Functional Type (PFT) datasets within five buffer radii (500 m–10 km). Random Forest models evaluated the relative importance of land-cover predictors at each spatial scale. Results SOM analysis revealed six ecologically distinct colony groups differing in species dominance, richness, and geographic distribution. Large-bodied species predominated in inland forested regions, whereas medium- and small-bodied species clustered in coastal and urban–rural mosaics. Environmental predictors were strongly scale-dependent: BUILT areas, managed grasslands, and water-related cover dominated at fine scales; natural grasslands, bare land, and tree-related PFTs—hallmarks of riparian corridors—emerged at intermediate scales; and regional land-use intensity remained the strongest predictor at 10 km. Conclusions Colony assemblages arise from hierarchical interactions among fine-scale habitat features, river-corridor landscapes, and broader-scale land-use regimes. This hierarchical multi-scale perspective provides a predictive framework for anticipating how land-use change will reorganize ecological networks supporting colonial waterbirds.