Spatial ecology of the water opossum Chironectes minimus in Atlantic Forest streams

The water opossum Chironectes minimus is the world's only semi-aquatic marsupial. It is considered rare, and it is reported on several regional conservation lists of species as either endangered or data deficient. Given its uniqueness and the poor knowledge of its ecology, we aimed to investigate home range size and overlap and habitat selection of the water opossum in Atlantic Forest streams in southeastern Brazil. We radio tracked water opossums and collected information about their habitats and behaviour from October 2004 to April 2010. We combined common home range estimators for animals living in linear habitats with the synoptic model of home range and habitat selection. For the 10 individuals monitored, the home ranges varied between 0.80 and 9.66 km of watercourses; none of them had exclusive home ranges. The home range size for males was, on average, three times larger than for females. The overlap data showed that, on average, one male could encompass the home ranges of up to five females simultaneously, but more than one male could have access to the same female. For habitat selection at the individual level, we could not find any strong influence of habitat features on water opossum preferences because individuals selected different sets of habitat variables. However, at the population level, we found a negative relationship between home range size and river size. The water opossum seems to prefer shallow and narrow watercourses to establish its home ranges. Here, we present valuable information to advance our knowledge of the water opossum and its ecology, which is urgent for conservation purposes. (C) 2016 Deutsche Gesellschaft fur Saugetierkunde. Published by Elsevier GmbH. All rights reserved.