Ecology of Oriental-australian Rear-fanged Water Snakes (colubridae: Homalopsinae) in the Pasir Ris Park Mangrove Forest, Singapore

We studied the ecology of four species of coastal marine.homalopsine snakes (OrientalAustralian rear-fanged water snakes) in the Pasir Ris Park mangrove forest, Singapore, using survey methods and radiotelemetry. The snake assemblage atPasir Ris (220 snakes collected) was dominated by Cerberus rynchops (72.7% of total snakes), amedium-sized piscivore. Three species of crustacean eaters were also present, but less common: Germ-da prevostiana (15.9% of total; medium-size, small head, slender body; diet of recently-molted crabs), Fordoniu leucobuliu (9.6% of total; broad head, stout body; diet of hardshell crabs), and Cuntoriu violuceu (1.8% of total; small head, slender, elongate body; diet of snapping shrimp). Size measurements indicated that sexual dimorphism was not pronounced, but we did find some sex differences in snout-vent length, tail length, and mass ‘among the four species. Surveys along a 200 m boardwalk transect showed that C. rynchops exhibited a strong habitat association with mangrove forest areas dominated by open muddy pools (-100 m of the transect) compared to areasdominated by mud lobster (Thalussinu unomulu) mounds (-100 m of the transect). The crustacean-eaters were often observed in association with mud lobster mounds, but we found no significant difference in the use of the mud lobster mound habitat zone compared to the mud pool zone for these species. A survey of snake activity indicated that the mangrove homalopsines were strongly nocturnal and active throughout he night. Gerurdu prevostiunu increased activity during spring tides, but the other species did not. Fordoniu leucobuliu was the subject of a short-term (five-week) radiotelemetry study. The three male snakes monitored were relatively ” sedentary and moved short distances when they did move (range = 1.8 to 14.0 m). Typical of tropical aquatic snakes, the body temperatures of the snakes monitored were very stable (range = 26.3 29.0°C) and similar to the microhabitat emperatures recorded. However, we found that snake body temperatures were consistently higher than the microhabitat emperatures recorded uring a 48-hour intensive monitoring period. Two of the monitored F. leucobuliu resided in the mud lobster zone of the transect and made extensive use of mud lobster mounds (100% of telemetric locations). The snakes did not exhibit a significant preference for any particular size class of mud lobster mound, and mounds were used in approximately the same proportion as their abundance. We discuss the community ecology and conservation biology of coastal marine homalopsine snakes with respect to the special characteristics of the mangal forest ecosystem, particularly mud lobster mounds and their burrow complexes. The once extensive mangrove forests of Singapore have been reduced to a series of degraded patches. Despite its small size, the Pasir Ris Park mangrove forest supports a rich, diverse community indicating that even small patches of mangrove can be important reservoirs of biodiversity and deserve preservation.