Using mangrove and field observation data to identify fine-scale species distributions: a case study in bockadams (Serpentes: Homalopsidae: ).

Characterization of species distributions is a fundamental challenge in biodiversity science, with particular significance for downstream evolutionary studies, conservation efforts, field-based faunal studies and estimates of species diversity. Checklists and phylogenetic studies often focus on poorly known, rare taxa with limited ranges. However, studies of widely distributed, ecologically important species that are abundant in their preferred microhabitats are also important for systematics and local conservation efforts, but less often studied. We collected novel natural history data during fieldwork (2019-2023) for Philippine populations of bockadams (Homalopsidae: ), one of the most abundant vertebrates in Southeast Asian aquatic systems. Considered a coastal snake, many studies report inland. We report the frequency of encounters of , and the IUCN data-deficient, Philippine-endemic during six expeditions (62 days; 1041 person-hours). We report new occurrence data for 69 and for coastal and inland populations, water measurements and dietary observations. Regression analyses and ecological niche models show the importance of coastal and mangrove habitats for . Our study is the most comprehensive assessment of Philippine populations to date and provides critical baseline natural history data for downstream research on widespread and range-restricted species of Southeast Asian snakes.