Monkeys Meet a Boa Constrictor

Here in northwest Costa Rica we have two species of monkeys; Mantled Howler Monkeys (Alouatta paliatta), which consistently wake us up at 5:15 each morning with their monstrous bellowing, and the White-faced Capuchin (Cebus capucinus), which is the more common of the two.  Where we live at Finca Pura Vida there is a troop of the latter, numbering about a dozen individuals, that comes by regularly to scour the yard in search of food.

Capuchins are the most well-studied of the New World primates; they are adaptable, absurdly intelligent, and have complex social hierarchies.  They travel in groups of up to several dozen individuals, methodically moving through forests, gardens, and backyards in search of ripe fruits, bird nests, small mammals, and insects.  When faced with a challenging prey item, Capuchins will hunt cooperatively; several times now I have watched the entire troop here at the Finca converge on a single Variegated Squirrel (a close relative of our familiar Eastern Gray Squirrel) to capture, kill, and share it - sort of a ghastly scene, not for the faint of heart.

Another scenario in which the entire troop behaves cooperatively is when they cross paths with a potential predator.  Several weeks ago we encountered a Boa constrictor, about 4' in length, crossing the dirt road near the Finca.  We bagged it and brought it back to the house for some photos, and it just so happened that the monkeys were in the yard (robbing the bananas from the bird feeder, as they do regularly, much to our continual frustration) when we extracted the Boa from the bag.  Instantly it was spotted by one of the young females of the group, who began sounding the alarm (sort of an outraged- and offended-sounding "UGH!").  Within seconds the entire troop had congregated on the roof nearby to inspect the danger, and to issue alarm calls of their own.

Interestingly, younger Capuchins will sound alarm calls much more frequently, and often inappropriately - they may scold harmless snakes, snake sheddings, and non-predatory birds, for example.  But they learn to discriminate between the harmless and the potentially threatening creatures as they get older and gain more experience.  An interesting hypothesis regarding snake-mobbing is that when older, more experienced adults sound the alarm to alert the group of a snake of the dangerous variety, they are helping teach the younger, inexperienced monkeys to differentiate between them and the harmless variety.

Adult male with a younger female reacting to a Boa constrictor

After about twenty minutes, the monkeys seemed convinced that the snake's presence was sufficiently announced, and dispersed to continue their routine vandalizing of the yard in search of food.  We photographed our boa and released him, well out of sight of the monkeys.