Population Density Estimates of the Critically Endangered Yellow-tailed Woolly Monkeys (Oreonax flavicauda) at La Esperanza, Northeastern Peru

The critically endangered yellow tailed woolly monkeys (Oreonax flavicauda, Humboldt 1812) are endemic to the cloud forests of northeastern Peru. We surveyed populations of Oreonax flavicauda in the Centro Poblado La Esperanza, Amazonas department between May 2008 and March 2009. We conducted census work in an area comprising disturbed primary cloud forest interspersed with pasture lying between 3 protected areas, all of which are known to contain populations of Oreonax flavicauda. We used standardized line transect methodology to census an area of ca. 700 ha. We also recorded group size and composition. We compared the results of transect width estimation, Krebs' method, and an ad libitum total group count. We calculated individual densities of 8.27/km(2) and 9.26/kmA(2), and group densities of 0.93/km(2) and 1.04/kmA(2) using Krebs' method and transect width estimation, respectively. Average group size was 8.9, with 1-3 adult males, 1-6 adult females, and 0-6 juveniles and infants. The results from our transect surveys coincided well with our estimated total group count. Our results are similar to those from previous studies, although differences in methodologies and site-specific environmental factors make comparison difficult, and suggest that Oreonax flavicauda is able to survive in disturbed habitat when hunting pressure is low.