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Salmon-bellied Racer

Rushing into a dense arrangement of aerial roots, an unidentifiable dark snake soon concealed itself at the center. I could only pick up on a faint striped beige pattern until it fled outward and elevated its head— revealing a bright orange underbelly. The species was a salmon-bellied racer (Mastigodryas melanolomus), and a very large and old individual, marked with scars all over its face and a completely impacted right nostril. The genus Mastigodryas comprises 13 species, most of which transition from a checkered color pattern with thin horizontal stripes as juveniles to having solely lateral stripes as adults. They are primarily ground-dwelling, but are great climbers and will frequently move throughout the low understory. On several occasions, I’ve spotted M. melanolomus sleeping high up in trees at night (conspicuously orange from below!), a habit not uncommon for terrestrial snakes to avoid predation from wandering mammals.

Salmon-bellied racers are lizard hunters, actively pursuing anoles, ameivas, and skinks, but rain frogs (Eleutherodactylus), ground snakes (Geophis), rodents, shrews, and other small leaf litter inhabitants supplement their diet. Their primary predation pressure comes from small to medium-sized raptors that specialize in eating snakes such as laughing falcons (Herpetotheres cachinnans) and also generalists like semiplumbeous hawks (Leucopternis semiplumbeus) and roadside hawks (Rupornis magnirostris). When captured directly, salmon-bellied racers opt for a less threatening and more practical method for escape. Gaping and body inflations are no more, and the snake will wrap its body around the predator tightly in an attempt to incapacitate it. Being unable to fly or move properly, the raptor will eventually reach a state of vulnerability that eclipses its desire for food, allowing the snake to escape once a grip can no longer be maintained. Although this may sound unusual, there is a beautiful record of such an interaction in southern Costa Rica, and as it happens, I narrowly missed another nearly identical account at La Selva in 2016. By the time I had run outside, the hawk and snake had both taken off in opposite directions…

Both snakes in this post photographed after disturbance [4]

Laughing falcon (Herpetotheres cachinnans), a common predator of swift diurnal snakes; photographed in situ [1]
Another leaf-litter dweller, the adorned graceful brown snake (Rhadinea decorata), a predator of rain frogs (Eleutherodactylidae) and their eggs

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