The taxonomy of Cacajao was reviewed by Hershkovitz (1987), who recognised four subspecies of bald-headed uakaris: Cacajao calvus calvus; C. c. rubicundus; C. c novaesi; and C. c. ucayalii.  Based on new information on the geographic distribution, molecular phylogenetics analyses, and the examination of museum specimens, the four subspecies recognised by Hershkovitz (1987) were raised to the species level – i.e., Cacajao calvus, C. rubicundus, C. novaesi, and C. ucayalii – and the population of white uakaris from the Tarauacá river basin, in Brazil, was described as a new species: Cacajao amuna (Silva et al., 2021). Therefore, five species of bald-headed uakaris are currently recognized.

Cacajao rubicundus is assessed as Least Concern, but given its relatively restricted range (three restricted, isolated areas in the middle Solimões River within an extent of occurrence of 35,000 km²) and low genetic diversity, it could be reassessed as Near Threatened or Vulnerable in the future. At the moment, the species ranges in a region that has low human population density. Furthermore, the species is only hunted occasionally and occurs in large protected areas. The main threat to this species is the impact of climate change.

Further studies are necessary to confirm the extent and abundance of this species, and to identify the potential threats. It is suspected that the population is declining but further information is required.

Cacajao rubicundus is endemic to Brazil, occurring only in the Amazonas State. The type locality is the north bank of the Solimões River, opposite the town of São Paulo de Olivença, Amazonas (Hershkovitz 1987). Silva et al. (2021) estimated the species’ Extent of Occurence to be 10,291 km², but occurring in three restricted and disjunct populations. Although the authors surveyed from the mouth of the Içá River to the Puretê River (near the Brazil-Colômbia border), they only recorded C. rubicundus in the flooded forests between the Solimões River and the Jacurapá channel – a right-bank tributary of the lower Rio Içá – in a range estimated of 2,328 km² (Silva et al. 2021). About 40 km from the Jacuarapá channel, on the south bank of the Solimões River, Silva et al. (2021), registered C. rubicundus on the left bank of the low Jutaí River, in the Jutaí-Solimões Ecological Station—an area estimated of 1,396 km². Cacajao rubicundus also occurs along the Auati-Paraná, a channel that connects the Solimões and Japurá rivers, in an area estimated of 546 km² (Silva et al. 2021). The disjunct distribution of C. rubicundus is a result of river rearrangements due to sedimentology and tectonic activity in central and western Amazonia (Silva et al. 2024). A contact zone between C. rubicundus and C. calvus was reported along the Aiupiá channel, a south bank tributary of the Auati-Paraná (Vieira et al. 2008).

For the purposes of this IUCN Red List assessment, the extent of occurrence has been calculated following IUCN methodologies as approximately 35,000 km².

A preliminary study using the distance sampling method estimated the population of C. rubicundus from the Auati-Paraná channel 41 individuals/km² (95% CI = 16.9–102.46, CV = 40.7), 5.1 groups/km² (95% CI = 2.1–12.5, CV = 35), and 8.1 individuals/group (95% CI = 5.2–12.6, CV = 20.78) (Silva et al. in prep). Genomic analyses indicated a very low effective population size of C. rubicundus populations – 723 (442-915) individuals in the Jutaí River, and 950 (743-1,116) individuals in the Içá River (Silva et al. 2024).

It is suspected that the population is decreasing.

There are no field data on the ecology of this species. Cacajao rubicundus is a habitat specialist of flooded forests and occurs mostly in the floodplain of the Solimões River basin (Silva et al. 2024).

Like other members of the Pitheciinae family, Cacajao has morphological adaptations in their mandibular muscles, as well as in their dentition, allowing the predation of seeds found in hard-shelled fruits that are usually consumed at an immature stage (Barnett et al. 2013). Thus, seeds and fruits are, probably, the main food items in the diet of C. rubicundus. They can be considered frugivorous specialised in immature seeds (Ayres 1986, Barnett et al. 2013).

Climate change is the main imminent threat to C. rubicundus with predictions of significant disruption of the annual precipitation cycle in the flooded forests in the region where this species occurs (Lynch et al. 2021). However, there is no study showing the effects of climate change on the species' habitat. Selective logging along the Solimões River may pose a threat, although rates of deforestation are very low in this region. The species has low genetic diversity and disjunct distribution (Silva et al. 2024, Hermosilla-Albala et al. 2024). The species may be occasionally hunted since juvenile individuals were registered as pets nearby São Paulo de Olivença (Maranhão, L., pers. comm.) but field studies are needed to verify the impact of both selective logging and hunting.

The species may be occasionally hunted since juvenile individuals were registered as pets nearby São Paulo de Olivença (Maranhão, L., pers. comm.) but field studies are needed to verify the impact of both selective logging and hunting.

This species is listed in CITES Appendix I.

It occurs in the Jutaí-Solimões Ecological Station (289,511 ha) (Silva et al. 2021) and the Mamirauá Sustainable Development Reserve  (1,124,000 ha) (Vieira et al. 2008).