Population estimates of the endangered Callithrix aurita and Callithrix hybrids records in a large Atlantic Forest remnant

Forest-dependent species are among the most threatened species due to landscape changes, and this is the case of the buffy-tufted-ear marmoset (Callithrix aurita), an Atlantic Forest endemic primate. Besides its extensive habitat reduction across Atlantic Forest, the species suffers from the negative impact of the presence of non-native congeners that threatens its local populations due to competition and hybridization events. Knowing the population status of this endangered species is important to guide conservation efforts. Thus, we estimated the population density of C. aurita and recorded the presence of invasive Callithrix species and Callithrix hybrids in Serra do Japi, a large forest remnant with mountainous terrain within the most human-populated region of the State of São Paulo, Brazil. We surveyed a 14.8 km² area with 387.2 km of survey effort. We estimated a sighting rate of 4.4 groups/10 km walked. The maximum number of individuals recorded per group ranged from 7 to 12. We identified 15 groups throughout the sampled area, totalling 1.01 groups/km². Two individuals from two distinct groups presented body pelage characteristic of hybrids between C. aurita and other Callithrix species. No individuals of other Callithrix species were recorded within the surveyed area. Considering the total size of this remnant and the potential population size of C. aurita inhabiting this area, this local population may be an important source of individuals for helping the conservation and long-term persistence of the species. However, the presence of Callithrix hybrids in the area is worrying and may threaten the local native population. Our study reinforces the concern with C. aurita conservation and the need for studies focused on the management of hybrids and invasive Callithrix species. Mitigation measures should be directed to readily control hybridization to keep this large population of Serra do Japi safe.