Multi-scale environmental drivers of heron and egret colony assemblages in Korea using self-organizing map clustering

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. 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. 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, 1 km, 3 km, 5 km, and 10 km. The relative importance of land-cover predictors at each spatial scale was evaluated using Random Forest models. 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 showed scale-dependent patterns: built areas, managed herbaceous vegetation, and water-related cover dominated at fine scales; natural grasslands, bare land, and tree-related PFTs emerged at intermediate scales; and broader land-use variables remained important at 10 km. 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 landscape-ecological framework for anticipating how land-use change may alter the multi-scale landscape contexts supporting colonial wading birds.