Brazilian gracile opossum habitats than more purely arboreal animals. It has also been found in artificial plantations. There are no recognised subspecies. Brazilian gracile opossums are arboreal and nocturnal, spending the day nesting in tree hollows. They are solitary animals, with each individual inhabiting a home range of anything from , depending on habitat. Males tend to have larger home ranges than females, presumably because, being larger, they require more food. The species is insectivorous, and is an opportunistic forager, not specialising in any particular kind of insect. Individuals have also been reported to eat some spiders, snails, and even fruit (including passionfruit).
Vicente Pérez Rosales National Park reeds. A diversity of animals of the rodent group live in the park. The larger ones are coipo, coypu, "Myocastor coypus", a webbed-feet animal that inhabits reedy lake and river banks; and Wolffsohn's viscacha, "Lagidium wolffsohni", of the family Chinchillidae, whose preferred habitat is above the timber line. Among the smaller rodents, scientists have shown particular interest for Chilean climbing mouse, "Irenomys tarsalis", and for the long-clawed mole mouse, "Geoxus valdivianus". The park is home to two species of marsupial mammals. Monito del monte, "Dromiciops gliroides", has a semi-arboreal habit. It has been discussed why this South American marsupial appears