Nancy Ma’s Night Monkey is part of the red-necked group of night monkeys, with a diploid chromosome number of 54 (Ford 1994). They are found in flooded and un-flooded tropical forest. Higher population densities have been found in flooded forests owing to the availability of tree holes, their preferred sleeping sites. Lowland swamp, pre-montane forests up to ~1,000 m asl. and inundated dense vine tangles are also used by Aotus nancymaae (Shanee et al. 2015; Aquino and Encarnación 1986a,b; Fernandez-Duque et al. 2013). In the Tahuayo River (Peru), A. nancymaae had 21.4% of its sleeping sites in the shrub stratum of the understory, 64.3% in the lower story and 14.3% in the middle story. No sleeping sites were found in the upper story or in emergent trees for this species (Aquino and Encarnación 1986a).

Night monkeys are generally nocturnal: they are most active at dawn and dusk. They are omnivorous; their diet includes fruit, nectar and flowers (seasonally important for A. a. azarae in the Chaco), leaves, and small animal prey such as insects (Wright 1989, Fernandez-Duque 2007). Nancy Ma’s Night Monkeys live in small groups that range from two individuals in hunting areas of north-eastern Peru (Maldonado and Peck 2014) to an average of 3.4 individuals in the Rio Tahuayo, northwestern Peru (Aquino and Encarnación 1988), and 3.06 individuals in Naranjales, Colombia where animals are extracted for malaria research (Roncancio et al. 2019).

They are socially monogamous, with extensive male care of offspring (Rotundo et al. 2002, 2005; Wright 1984, Wolowich and Evans 2007), living in small groups of an adult pair and offspring of different ages (infant, one or two juveniles and sometimes a subadult). There may be subadults that have left their natal groups or older adults which have been evicted from their groups by competitors (Fernandez-Duque and Huntington 2002, Fernandez-Duque 2004). Both sexes disperse. Night monkeys are territorial—groups occupy overlapping territories of 1-18 ha (depending on the species, location and level of habitat fragmentation) (Wright 1978, Fernandez-Duque 2007, Garcia and Braza 1987, Castaño et al. 2010, Shanee et al. 2013a). Wright (1994) and Fernandez-Duque (2007) review the behaviour and ecology of the genus.

A peak in births has been reported for A. nancymaae between December and March, during the rainy season, and age of first reproduction is approximately 40 months. Interbirth intervals in captive females are 9-11 months (Aquino et al. 1990, Fernandez-Duque et al. 2013). In a social study conducted by Wolowich and Evans (2007) on a captive colony, they reported that A. nancymaae possess a unique composite of communicative behaviors. Most social interactions between mates consist of anogenital- and nose-sniffing, urine-rinking, and partner-marking with the subcaudal gland. They also reported the frequent use of a variety of potential chemical signals including scent-marking with their muzzles, sternal glands, and subcaudal glands as well as urinating and urine-washing.

Size:
In Captivity: Adult male weight averages 0.946±0.14 kg (n=4, range 0.750-1.08 kg), adult female weight 0.907±0.124 kg (n=6, range 0.706-1.05 kg) (S. Evans, unpubl., in Fernandez-Duque 2007).

In the Brazilian-Peruvian Amazon, Aotus nancymaae occurs south of the Rio Amazonas, west from the Rio Jutaí. Its southern limit is in the headwaters of the Rio Jutai, stretching west in a line to cross the Río Javari at the level of the headwaters of the Río Tapiche, across the Ucayali basin to the upper Río Marañón (Hershkovitz 1983; Aquino and Encarnación 1988, 1994a). The northern boundary in Peru is the right bank of the Amazonas to the Río Marañón, occurring to the north of the Marañón between the ríos Tigre and Pastaza (Aquino and Encarnación 1994), overlapping the distribution of A. vociferans north of the Amazonas and Marañón. The western boundary of the species' distribution in Peru is the Andean foothills in San Martin up to ~1,000 m above sea level (Shanee et al. 2015). In Colombia, the distribution of A. nancymaae is uncertain due to the existence of a possible endemic subpopulation and an introduced subpopulation. Bloor et al. (2012) report the species north of the Amazon River, west from San Juan de Atacuari, border with Peru. Maldonado and Peck (2014) reported the predicted distribution of A. nancymaae in Colombia, where the species has been released after malaria research. Although the species is present all along the Amazon River, the distribution of the endemic subpopulation is limited to the Loretoyacu River basin. In Colombia its distribution range is approximately 652 km² (SINCHI 2015).

• Jutaí-Solimões Ecological Station (287,101 ha) (in range).

• Pacaya-Samiria Natural Reserve (2,080,000 ha) (Aquino and Encarnación 1994b)
• Manu National park (1,532,806 ha) (Aquino and Encarnación 1994b)
• Tamshiyacu-Tahuayo Communal Reserve (Aquino and Encarnación 1994b).