The yellow-tailed woolly monkey (Oreonax flavicauda) is endemic to a small area of montane cloud forest dominated by Ficus spp. in the Peruvian departments of Amazonas and San Martin (Leo Luna 1980) and neighboring areas of the departments of Huánuco and La Libertad (Graves & O'Neil, 1980; Parker & Barkley, 1981; Shanee, 2011). This species is listed as Critically Endangered on the IUCN Red List of Threatened Species (2008, A4c) and Endangered on Appendix 1 of CITES (2005). The main threats to O. flavicauda are massive deforestation for agriculture, subsistence hunting, logging and mining (deLuycker, 2007; Leo Luna, 1980; Shanee, 2011). In many areas habitat loss has forced this species into small forest fragments (Shanee et al., 2007; Shanee, 2011).
Minimum altitudes where O. flavicauda has been observed in previous studies.
On the 25th and 26th of January 2013, while carrying out distribution surveys of the Andean night monkey (Aotus miconax), we encountered a group of O. flavicauda 14.5 km west of the city of Uchiza in San Martin department in an area known locally as Tingo de Uchiza (S 8°28′47.04″, W 76°35′24.90″), just north of the border with Huánuco (Fig 1.). The group was found along an existing 1.1 km trail at altitudes between 1,084 and 1,373 m. a.s.l., just under 500 m lower than previous observations (Table 1). We observed the group feeding on fruiting figs (Ficus spp.) for 25 minutes before they crossed a small stream which feeds the Rio Trisneja where we were unable to follow. The group consisted of 12 individuals, including two females with infants.
The habitat was similar to that described by previous researchers (Shanee, 2011; Shanee & Shanee, 2011) with high humidity (up to 99% relative humidity at 14.7°C). Forests in this area are dominated by Moraceae (Ficus spp.) and Cecropiaceae (Cecropia spp.) as well as Fabaceae (Inga spp. and Erythrina spp.), Icacinaceae (Citronella spp. and Styloceras spp.) with a high density of epiphytes. Our observations were made in a long thin canyon with steep sides that culminated in the 400 m high Velo de Plata waterfall. It is possible that the extremely humid and cool microclimate created by the local topography and the effect of the waterfall have allowed the higher altitude forest type, which is home to O. flavicauda, to establish itself at these lower altitudes.
Local villagers stated that O. flavicauda is common in the area, which they had mistakenly identified as howler monkeys (Alouatta sp.). When informed about the species endemism and Critically Endangered status they showed a lot of interest in conserving the species. The Municipality of Uchiza is currently working with the San Martin Regional Government to create a new Regional Conservation Area (Area de Conservación Regional) which covers the area where our observations were made. More time will need to be spent in this area to see how much lower the species distribution reaches in this and other similar areas. With the current high rates of habitat loss throughout this species distribution area, any additional areas of habitat suitable for them are of importance for its conservation.