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An endangered red-backed squirrel monkey (Saimiri oerstedii citrinellus). To get a sense of the diminutive size of these delightful and clever monkeys, the tree trunk on which this mid-size youth is perched is 23 centimeters (9 inches) in diameter. Click image to enlarge.

Not content with waiting his turn in line, this playful little fellow is poised for a ten-foot leap down to a one-inch wide rope three stories above the ground. There he will join several members of his troop who arrived first at the rope and are "hogging" it.

Costa Rica's smallest and rarest primate [1], the critically endangered red-backed squirrel monkey (Saimiri oerstedii citrinellus), or "mono tití" as it is locally known, makes its home in the moist, tropical southern Pacific lowlands of Costa Rica at Quepos and nearby Manuel Antonio National Park (9.24 N, 84.10 W). Found nowhere else, the total population is estimated at just 1,200 individuals.

One of two subspecies native to Costa Rica, the tití is closely related to S. o. oerstedii found further south near Panama. It is thought that migrating pre-Columbian South American Indians kept these primates as pets, some of whom escaped back into the wild. Over thousands of years, these subspecies became geographically separated and biologically distinct.

The tití is characterized by the distinctive reddish fur "saddle" down its back and the grays of its head, shoulders and flanks. These are the only monkey in Costa Rica lacking a prehensile tail. They are masters at converting gravitational potential energy into kinetic energy and back again, as they travel from each tree branch to the next. Troops of ten to sixty-five individuals occupy the forest canopy and leap playfully, sometimes dive-bombing one another with mangos. Newborns ride atop their mothers' backs, hoping to escape the notice of boa constrictors, tayras (a kind of weasel), and the collared forest falcons who prey upon them. We are forewarned of the daily migration of the troops near our home by noting where the falcons are circling and swooping above. Titís that escape their predators can live twenty-one years, the females bearing young every 13-14 months after their first two years of life.

Manuel Antonio National Park was created in part to protect the habitat of these delicate creatures. But the park is visited by some 800,000 tourists per year. Human encroachment into the mono tití's habitat has created new threats from traffic where roadways have been laid across their migratory pathways. Accidental electrocution on power lines and inappropriate feeding and overfeeding by people have taken their toll.

These risks are being mitigated by local volunteer groups such as Kids Saving the Rainforest (KSTR), both by direct action and through education. Our kids are active members of KSTR, spending their Saturday afternoons on local project work.

KSTR provides a fine example of how amateurs and young people can make a real difference and do good science while having fun. Safety ropes ("monkey bridges") are being strung high above roads and power lines that intersect with mono tití migration routes. KSTR also plants trees and posts flyers in local businesses that inform tourists and local residents of the issues affecting the species' survival. Founded by and composed of preteens and teenagers, KSTR's hard work and positivism have earned international recognition by the Smithsonian Institution, National Geographic Kids and other organizations.

Photo metadata: Camera: Nikon D100 CCD; Lens: Nikon AF-S VR-Nikkor 70-200mm 1:2.8G with Nikon AF-S TC-20II (2x) Teleconverter: operated at 400 mm f/5.6 exposure 1/640 sec; 0 EV compensation at ISO 400; handheld at approx. 100 ft range. 8-bit jpeg format 3008 x 2000 pixels; image is unretouched. Exposed 1-May-2004 at 12:38:12.9 PM CST by the author.

1. Henderson, Carrol L. 2002. Field Guide to the Wildlife of Costa Rica 1st ed. Austin: Univ. of Texas Press: 456-459.