Abstract/Summary

Diel activity patterns are an important aspect of wildlife ecology and evolution and provide valuable information for conservation and monitoring, yet for many species activity patterns remain unstudied and may be presumed to mirror related taxa. Here we describe the distinct diel patterns of an endemic population of venomous sea snakes Hydrophis platurus xanthos inhabiting a narrow range (circa 320 km2) in Golfo Dulce, Costa Rica. To investigate we conducted a systematic visual survey over five 24-hour cycles and evaluated 339 hours of previously obtained sighting data from different studies spanning a decade. While sporadic diurnal surfacing does occur, mostly for respiration, our observations revealed marked crepuscular peaks with regular surfacing through the night. We also report on observed surface behaviors that were also found to vary in frequency at different phases of the photoperiodic cycle. In particular, we show feeding as more common at night. Hydrophis platurus xanthos has developed a circadian rhythm that differs noticeably from its taxonomic parent (H. p. platurus is reported as diurnal across its Indo-Pacific range) and no congeners have been categorized as crepuscular. Our work thus contributes to the ecological knowledge of this evolutionarily distinct marine elapid and offer insights into the potential role of environmental conditions in shaping animal activity.