Group dynamics and habitat use of the Giant Otter, Pteronura brasiliensis (Zimmermann, 1780), in seasonally flooded forest in the Araguaia River, Central Brazil: A 10-years study.

Abstract

We carried out monthly surveys of the giant otter population between 2010 and 2020 in a study area comprised of 1,500 hectares of igapo flooded forest with oxbow lakes in the Cantao region of central Brazil. We recorded 16-32 resident adults in the study area each year, distributed in 4-8 groups. Resident groups exhibited extensive home range overlap, with each group using several lakes and larger lakes used in rotation by up to six groups. Dens and campsites were also shared by multiple groups, but lakes were used by only one group at a time, and encounters between groups were very rare. 24 adult otters were observed to join an existing group. Some individuals changed groups multiple times. Resident adult turnover was high. Each year an average of 36% of resident adults were new immigrants, and 72% of groups left the area within two years. Resident groups had, on average, one litter every three years, and annual cub production showed high variability and a negative correlation to the number of new immigrants in the area. No pairs of giant otters reproduced successfully during the study. Groups of three otters formed through the recruitment of an adult individual by an existing pair and reproduced as successfully as larger groups. Group dynamics and territorial behavior in the Cantao flooded forest ecosystem, where optimal giant otter habitat is continuous in all directions, were found to be different from that reported in areas composed of patchy (isolated oxbow lakes) or linear (rivers) habitat. This suggest that giant otter social and territorial behavior is plastic and adapts to the spatial characteristics of the habitat.