New records of the southern muriqui (Brachyteles arachnoides) in Serra da Mantiqueira through thermal drones.

Muriquis (Brachyteles sp.) are endemic to the Brazilian Atlantic Forest; its genus is divided into two species, the northern muriqui (Brachyteles hypoxanthus), and the southern muriqui (Brachyteles arachnoides), both assessed as Critically Endangered by the IUCN Red List. The endangered status of muriquis is associated with habitat loss, fragmentation, hunting, and other anthropogenic actions, confining the species to fragments, mostly, in protected areas. One of these important protected areas is in the Serra da Mantiqueira, the Environmental Protection Area Serra da Mantiqueira, that has a sizable continuous remnant of the Atlantic Forest with a high degree of biological diversification, where both species of muriquis occur. This designation highlights the region as one of the most critical regions for the genus Brachyteles. Nonetheless, new records may fill gaps in the distribution limit between the two muriquis species, identifying whether there is a possible barrier or possible overlapping area. However, recording and estimating primate populations over large areas through standard field techniques, such as linear transects, can be costly in terms of time and financial resources. In addition, given its altitude gradient, the Serra da Mantiqueira region is remote and difficult to access for systematic biodiversity surveys. Thus, aerial surveys were carried out using thermal sensors attached to drones, which made it possible to record two new groups of southern muriquis in Serra da Mantiqueira. Thus, we confirm that this new method represents an effective way to survey highly threatened primates.