A Detailed Evaluation of the Suitability of Waterbird Habitats in Hangzhou Bay National Wetland Park—A Differential Analysis of Wading Birds and Swimming Birds

Hangzhou Bay is an estuarine ecosystem on the Yangtze River Delta and a key wintering habitat for waterbirds. However, suitable waterbird habitats have been degrading and fracturing. Therefore, we aimed to assess waterbird habitat suitability and identify the principal factors affecting quality in Hangzhou Bay National Wetland Park. Habitat suitability index (HSI) models were constructed for wading and swimming birds using water source conditions, disturbance levels, concealment, and food abundance. The models adopted consistent factor weights but differentiated the grading criteria for the waterbird groups. Applicability was validated using bird survey data collected in 2025, and habitat suitability was quantitatively assessed using field and literature data. Food abundance and water source conditions were dominant factors influencing habitat suitability; concealment and disturbance levels had minor effects. The abundances of wading and swimming birds increased with HSI values, although limited validation sites constrained these relationships. Positive trends indicate that the HSI models may capture the spatial variation in habitat use. Grade III or higher areas comprised 96.67% and 74.21% of the total area for wading and swimming birds, respectively; no Grade I habitats were identified. Overall, the study area provided favorable habitats for waterbirds, although habitat suitability differed between the groups. These findings may provide a quantitative reference for the targeted conservation and restoration of waterbird habitats in the Hangzhou Bay wetland.