According to Hershkovitz (1987) Cacajao calvus ucayalii, listed as Vulnerable by the IUCN, (Veiga & Bowler, 2008) is distributed from the east bank of the Rio Ucayali in an easterly direction to the Rio Yavarí and from the Rio Amazonas in the north to the Rio Urubamba in the south. Hershkovitz (1987) also includes the east bank of the lower Yavarí in Brazil, but its presence there has not been confirmed and it is possible that museum specimens marked as collected on the Brazilian bank of the Yavarí actually came from the Peruvian side where this primate is locally abundant. Surveys conducted between 1979 and 1986 (Aquino 1988) showed that the range was much reduced, hunting having exterminated the species in several areas. Aquino (1988) suggested that the southern limit is now probably the Rio Sheshea and that populations close to the Rios Ucayali and Amazonas have also been reduced and in some areas populations have been exterminated (Fig. 1). Populations of Cacajao calvus observed by Peres (1997) on the upper Rio Juruá and unconfirmed reports by Fernandes (1990) in the Brazilian state of Acre on the upper Juruá and Purus are either of Cacajao calvus novaesi or Cacajao calvus ucayalii, which would extend the known ranges of either of these subspecies.

The Rio Ucayali is the largest tributary of the Rio Amazonas and at 400–1,200m wide presents a significant barrier to primate populations. However, the constantly-changing course of the river means that very large islands of forest big enough to support small primate populations effectively cross from one side of the river to the other as oxbow lakes are formed, particularly near the mouth of the river where it meets the Rio Marañon to form the Rio Amazonas. Cacajao calvus calvus has been found on both sides of the Rio Amazonas (Sousa e Silva Júnior and Martins 1999), demonstrating that the ranges of subspecies of Cacajao calvus can traverse major river barriers. Isolated reports of red uakari monkeys west of the Ucayali on the Rio Yanayacu, a tributary of the Rio Marañon, running more or less parallel to the Rio Ucayali, in the Pacaya-Samiria National Reserve (PSNR) have occurred for a number of years. Until now, these reports have been unconfirmed. Rumoured sightings have emanated largely from the community of Yarina on the Rio Yanayacu, a seasonally blackwater stream about 40m in width flowing exclusively through white-water varzea forests in the Pacaya-Samiria National Park. The Yanayacu flows 158 km from Lago El Dorado, to meet the Rio Marañon 30km upstream from the city of Nauta. Yarina was founded in the PSNR in the 1980s, and for this reason most of the adults in the community have not lived in Yarina or the PSNR all their lives. The NGO ProNaturaleza has worked with the communities on the Yanayacu for various years, and has coordinated a successful community-based conservation program here. Hunting for wild meat is not a principle activity in Yarina, and there are healthy populations of wild animals.

In September 2006, we made a short expedition to conduct interviews in Yarina and search the site for red uakari monkeys. Although red uakaris were not encountered during this expedition, several residents of Yarina reported seeing red uakari monkeys, usually in small groups on the banks of the river. Only two residents of Yarina regularly hunt, and both reported infrequent observations of groups of 20 or more uakaris. In addition to the recent observations, 3 older men (one from Yarina and two from the small nearby village of Arequipa) claimed to have seen red uakari monkeys years ago, when they used to make hunting and fishing expeditions into the forest. There was a high level of consistency between interviews, and considerable detail was given within some of the interviews. The observations were virtually all within an area of about 200km² (20,000ha) bounded by a large bend in the Rio Yanayacu (Fig. 2).

Figure 1.

The original distribution of Cacajao calvus ucayalii (Hershkovitz, 1987), the distribution in 1986 (Aquino, 1988) and the newly discovered population. Map adapted from Aquino (1988).

On three days between 3-10-2008 to 5-10-2008, during investigations on the Rio Yanayacu for a project on Giant Otters Pteronura brasiliensis, Mark Bowler from the Durrell Institute of Conservation and Ecology and Tony Laiche from the community of Yarina visited Quebrada Ahuara, a site highlighted during interviews in 2006 as one where persistent sightings of red uakaris occurred. At 10am on 3^rd October 2008, we encountered a group of red uakaris near Quebrada Ahuara (04°56′19.9″S, 74°08′26.1″W) (Fig. 2). We followed the group for one hour and 10 minutes covering at least 900m, but the uakaris were nervous and fled throughout the encounter. During the follow, we counted at least six individuals including at least one adult male, an adult female carrying a baby, a juvenile, and two older juveniles or sub adults. From the contact calls given by the monkeys, we estimated that the group contained at least ten individuals. Four clearly-different individuals were photographed (Fig. 3). We searched the area around the sightings for several hours on the following two days, but were unable to relocate the group. These new observations and interviews confirm the presence of the species on the west bank of the Ucayali extending the known range of Cacajao calvus ucayalii into the PSNR (Fig. 1). Until this discovery, the only protected area known to contain the subspecies was the regional Tamshiyacu-Tahuayo Communal Reserve, and while managing hunting is seen as the priority in this region (Bodmer 1995), protected areas play an important role in national and regional conservation strategies and conservation projects often focus around these areas.

Figure 2.

Locations of red uakari sightings on the Rio Yanayacu given in interviews (open triangles) and by Mark Bowler on 3-10-2008 (closed triangle).

The confirmation of red uakari monkeys in the PacayaSamiria National Reserve adds a new primate to the species list for the reserve, bringing the total number of species to 13. This is an extremely diverse primate community and one unequalled in areas of extensive várzea. The striking appearance and rarity of this monkey means it is used as a flagship species and as focus for conservation efforts in the Peruvian Amazon and will may prove a draw for tourism on the Rio Yanayacu, even though sightings of the monkeys would probably be very infrequent. Tourism already appears to be working well within the successful management plans for the area overseen by ProNaturaleza.

Figure 3.

Four recognisably different red uakaris photographed on the River Yanayacu on 3-10-2008 by Mark Bowler; a) Juvenile, b) juvenile/subadult, c) juvenile/subadult, d) adult male.

Informal conversations with people from the communities of Yarina and Manco Capac who were working in the community guard posts around Lago El Dorado and on the Yanayacu during our expedition, mentioned that large groups of uakaris used to inhabit the area around the community of Manco Capac in the Reserve, on the bank of the Ucayali River contiguous with the forests around Quebrada Ahuara. However, the species had not been seen there for 10 or 20 years. Higher levels of activity on this river in the past, from illegal loggers and people entering the reserve to extract resources have probably reduced densities of this primate by hunting. The uakaris observed at Quebrada Ahuara were very nervous, and fled from investigators. This suggests that the group may have experienced hunting in the past. However, the area is now protected by members of the community of Yarina, who do not hunt this primate. This small population of uakaris would be extremely vulnerable to illegal hunters entering the reserve from the Rio Ucayali. Although a detailed census has yet to be conducted, the population must be extremely small, may be experiencing inbreeding, and it will require special consideration if it is to persist. The population in the PSNR is the only known population of the subspecies Cacajao calvus ucayalii occurring in the complete absence of non-flooding terra firme forests. Establishing the size and composition of this population will be essential in estimating its viability, and putting in measures for its conservation. Monitoring the population in the long term might also give an idea about how this species might fare when its densities are low. More complete census is therefore required. Community groups and ProNaturaleza will then have to consider conservation actions for this primate.