Swift-moving diurnal snakes with acute vision are thrilling to find, whether it be whip snakes (Demansia sp.) in Australia, coachwhips (Masticophis sp.) in the U.S., or the subject of this post— the neotropical large-scaled sipo (Chironius grandisquamis). My first encounter with one was at La Selva when I was taking notes on Anolis lizards. A subadult sipo slithered under my legs and raised its head to survey its surroundings… a split second later and it had vanished. Since then, I’d only gotten glimpses of them as they rocketed away from my footsteps, with exception of one stripey juvenile and another occasion where a brisk chase ended empty-handed at a buttress. This past summer, I was ecstatic to find several adults, all near slow-moving streams. One slept coiled in overhanging vegetation and another two darted along the embankments. Indeed, of the 23 species in the genus Chironius, most have strong associations with riparian environments. They are adept at navigating in streams, and I have also observed one individual submerge itself under large rocks for more than 10 minutes. Chironius grandisquamis feeds mostly on frogs, even poison frogs (Phyllobates sp.) and mucus-secreting Trachycephalus & Leptodactylus, but they will opportunistically take salamanders (Bolitoglossa sp.), lizards, and small birds. Their high speed and manueverability makes them excellent predators on any substrate, along the ground or high in the forest canopy.
All sipos photographed after disturbance