The Nicobar long-tailed macaque (Macaca fascicularis umbrosa, popularly known as the Nicobar monkey) is a subspecies of the crab-eating macaque (M. fascicularis), endemic to the Nicobar Islands in the Bay of Bengal. This primate is found on three of the Nicobar Islands—Great Nicobar, Little Nicobar and Katchal—in biome regions consisting of tropical and subtropical moist broadleaf forests.