Ecology of southern muriquis (Brachyteles arachnoides) in the Área de Proteção Ambiental Barreiro Rico, São Paulo, Brazil

The Southern muriqui (Brachyteles arachnoides), the largest primate in America, is endemic to the Atlantic Forest in southeast Brazil. Its westernmost distribution is in the Área de Proteção Ambiental (APA) Barreiro Rico, in the interior of São Paulo state. This area has some forest fragments surrounded by pasture and sugarcane, eucalyptus and citrus plantations, but has a very rich biodiversity. The first register of muriquis in the APA Barreiro Rico dates from the 70’s; since then, there has been some research in the 80’s and again in the 00’s, mainly studying the ecology and behaviour of muriquis and other primates. In 2022, a primate survey indicated a decline in the muriqui population size, raising concerns for local species conservation and the need for updated information. Our research is divided into three chapters. (1) In order to know the real size of the B. arachnoides population, we did a primate survey with thermal drones flying over eight forest fragments. In 127 flight hours covering 2,947 km, we recorded only 12 southern muriquis, in two groups across two fragments: one on private property and the other in the public protection area Estação Ecológica (ESEC) Barreiro Rico. (2) The second chapter aimed to compare some variables in two forest fragments, where there were registers of muriquis in the past (São Francisco do Tietê (SFT) Farm) and where they live now (ESEC Barreiro Rico). To test whether the number of food resource species and the number of larger trees were important variables in the species’ occurrence, hypothesizing that they would be higher in the ESEC Barreiro Rico, where they occur nowadays. We implemented 10 plots (900 m² each) across those forest fragments. 943 trees with DBH > 5cm were measured, and samples were collected for further identification. The number of larger trees in both fragments is similar, the number of food resource trees is higher in the SFT Farm, but the proportion of the basal area of food resource trees is higher in the ESEC Barreiro Rico, indicating a possible preference for larger food patches. But, as the differences were small, we also raised the possibility that the legalized hunting of invasive species and, especially, forest fires play a major role in the population decline. The last part of this work (3) monitored the small group present in the ESEC Barreiro Rico to study their behaviour and diet, and to determine whether there is seasonal variation in their activities and food consumption throughout the year. We monitored them between July 2023 and August 2024, recording their location, activity and height in the tree. We also monitored 642 trees in the plot at ESEC Barreiro Rico to study phenology and compare the availability of items with their consumption. We analysed 28 days with more than 10 scans from the adults in the group. They preferred taller trees, where they spent most of their time resting, followed by feeding, locomotion, and socializing. Only resting had a seasonal difference. There is no difference in their diet by item between the wet and dry seasons. Leaves and flowers were the most-consumed items, followed by seeds. And they had a strong preference for certain items, such as ripe fruit and flowers. All the information collected during this research is very helpful for understanding their behaviour and habitat use, and for improving decisions about local conservation efforts for the species. Keywords: thermal drone; forest inventory; phenology; behavioural monitoring