Abstract
Conservation of breeding habitats is essential for sustaining populations of endangered waterbirds, yet quantitative links between breeding behavior and environmental drivers remain poorly understood. Saunders's Gull (Saundersilarus saundersi), a globally endangered species, has its largest breeding population in the Liao River Estuary National Nature Reserve (LRENNR), China. We integrated field survey data (53 sampling points, 24 environmental variables) with Maximum Entropy (MaxEnt) modeling and GIS analysis to identify suitable breeding habitats and key environmental drivers. Wet grassland was the dominant land-use type (40.17% of the study area). Elevation, wind speed, soil pH, and soil electrical conductivity collectively explained 70.90% of breeding habitat suitability, with higher predicted breeding occurrence probability associated with ranges of 13.80-16.97 m, 19.50-23.78 km/h, pH 6.65-7.50, and > 7,821.00 µS/cm, respectively. Only 2.05% (0.0802 km2) of the study area was identified as highly suitable habitat, highlighting the limited availability of potential breeding sites. These findings provide quantitative evidence for spatially targeted conservation planning and demonstrate the value of combining species distribution modeling with field-based behavioral analysis for endangered waterbird conservation.