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. White uakari populations were recorded in the Jurupari (Silva Jr & Martins, 1999), Pauini (Sampaio et al., 2018), and Tarauacá (Silva et al., 2021) rivers near the border of the Amazonas and Acre State, in Brazil. The taxonomic status of these populations, however, was unclear (Silva Jr & Martins, 1999; Silva et al., 2021). 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 was described as a new species: Cacajao amuna (Silva et al., 2022). Therefore, five species of bald-headed uakaris are currently recognized.

Cacajao calvus is considered Least Concern since most of the species distribution is legally protected in an area with relatively low human population density. The species is not hunted (Perreira et al. 2019). Climate change is the main imminent threat to C. calvus with predictions of significant disruption to the annual precipitation cycle in the flooded forests 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.

Cacajao calvus is endemic to the Amazon Rainforest, in the Amazonas State, Brazil. The species has a disjunct distribution, occurring on opposite sides of the Solimões River (Silva et al. 2021, 2024). Cacajao calvus is present in the confluence of the Solimões and Japurá rivers, almost entirely inside the Mamirauá Sustainable Development Reserve (Mamirauá SDR) (Ayres 1986, Hershkovitz 1987, Vieira et al. 2008, Silva Jr et al. 2013, Cardoso et al. 2014, Silva et al. 2021). In this region, the species is limited by the Auatí-Paraná on the north, while the Paraná do Maiana channel and Paraná do Aiupiá channel are the western limit – where the species forms a contact zone with C. rubicundus (Vieira et al. 2008). This area was estimated at 11,403 km² (Silva et al. 2021).

On the southern bank of the Solimões River, C. calvus occurs mostly in the lowland forests of the Jutaí-Riozinho interfluve (Silva et al. 2021, 2024). The species was also recorded on the western bank of the lower Juruá River in the proximities of Paraná Breu and Breuzinho – tributaries of the Juruá River (Cardoso et al. 2014). The geographic range of these populations was estimated at 16,780 km².

White uakaris were recorded in the Jurupari River – a tributary of the Tarauacá River (Silva Jr. & Martins, 1999) and in the Pauini River – a left-bank tributary of the Purus River (Sampaio et al. 2018). These populations, however, were considered as a different species, Cacajao amuna (Silva et al. 2022).

Population abundance was estimated in the Mamirauá Reserve by Ayres (1986) and Paim (2005). In the first study, 10 individuals/km² were estimated in five localities (Ayres, 1986); while in the second, 17 individuals/km² were estimated in six localities (Paim, 2005). An ongoing study using the distance sampling method estimated the population of the Mamirauá Reserve in 21 individuals/km² (95% CI = 11.6–37.8, CV = 30.2), 3.5 groups/km² (95% CI = 2.4–5.0, CV = 17.9), and 6 individuals/group (95% CI = 3.7–9.6, CV = 24.31) (Silva et al., in prep). In addition, the population of C. calvus from the Jutaí River was estimated at 5.3 individuals/km² (95% CI = 1.7–16.5, CV = 55.7), 0.12 groups/km² (95% CI = 0.3–0.4, CV = 53.55), and 41.2 individuals/group (95% CI = 30.2–56.4, CV = 15.3) (Silva et al., in prep). The population is suspected to be stable.

Most of the available information on the ecology and behaviour of Cacajao calvus is limited to studies carried out during the 1980s (Ayres 1986, 1989), mainly at the Mamirauá SDR. This species was initially considered a habitat specialist limited primarily to the white-water flooded habitats – várzea forests (Ayres 1986, Barnett and Brandon-Jones 1997). However, new records of C. calvus in the Jutaí River – a black water river – show that the populations from the south bank of the Solimões River may be exposed to a greater variety of habitats than the populations from the Mamirauá SDR.

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 the main food items in the diet of C. calvus. They can be considered frugivorous specialised in immature seeds (Ayres 1986, Barnett et al. 2013).

The groups are large, sometimes with more than 50 members. There are social subunits, or subgroups, operating in a fission-fusion system, which is a characteristic of the genus Cacajao (Ayres 1986, Bowler and Bodmer 2009). But there have been few studies focusing on this social dynamics, and other aspects of the social system of Cacajao (Bowler and Bodmer, 2009). The seasonal variation in the abundance of key resources (Ayres 1986, Bowler and Bodmer, 2011) may be an important selective pressure shaping the social system of C. calvus (Bowler et al. 2012). The main group studied by Ayres (1986) was composed of 45 individuals, who often split into foraging subunits; larger units were found during the flooding season, when there was a greater availability of fruits.

Habitat loss due to climate change is the main imminent threat to C. calvus with predictions of significant disruption of the annual precipitation cycle in the flooded forests 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). Cacajao calvus is not hunted. In ten years (2003-2013) of a hunting monitoring program at the Mamirauá Sustainable Development Reserve, in Brazil, 4,218 hunting events were recorded, with 10,992 animals harvested and consumed in the monitored communities – Cacajao calvus was not listed in any event (Pereira et al. 2019).

Hunting is not a major threat to this species (Pereira et al. 2019). The species is occasionally kept as a pet near the Jutaí River. There has only been one (non-confirmed) record of an individual captured for the international illegal trade of wild animals.

This species is listed in CITES Appendix I.

The species is officially protected in Brazil, and the major strategy applied is the National System of Protected Areas (SNUC). Most of the geographic range of Cacajao calvus on the north bank of the Solimões River is protected by Mamirauá SDR - Ramsar site no. 623. On the southern bank, the species occur in the Jutaí River Extractive Reserve (Jutaí RER) and at the Uacari Sustainable Development Reserve (Uacari SDR. While the Jutaí RER is a Federal Protected Area, the Mamirauá and Uacari SDRs are both under Amazonas State jurisdiction.