Each animal species selects specific microhabitats for protection, foraging, or micro-climate. To understand the distribution patterns of small mammals on the ground and in the understorey, we investigated the use of microhabitats by small mammals in a deciduous forest of southern Brazil. Ten trap stations with seven capture points were used to sample the following microhabitats: liana, fallen log, ground litter, terrestrial ferns, simple-trunk tree, forked tree, and Piper sp. shrubs. Seven field phases were conducted, each for eight consecutive days, from September 2006 through January 2008. Four species of rodents (Akodon montensis Four species of rodents (Akodon montensis Four species of rodents ( , Sooretamys angouya, Oligoryzomys nigripes and Mus musculus) and two species of marsupials (Didelphis albiventris and Gracilinanus microtarsus) were captured. Captured species presented significant differences on their microhabitat use (ANOVA, p = 0.003), particularly between ground and understorey sites. Akodon montensis selected positively terrestrial ferns and trunks, S. angouya selected lianas, D. albiventris selected fallen trunks and Piper sp., and G. microtarsus choose tree trunks and lianas. We demonstrated that the local small-mammal assemblage does select microhabitats, with different types of associations between species and habitats. Besides, there is a strong evidence of habitat selection in order to diminish predation.

Movements under environmental structures and on supports, and the use of shelters by Akodon montensis were assessed using the spool-and-line technique. Movements of a few individuals of Thaptomys nigrita, Brucepattersonius iheringi and Oligoryzomys nigripes were also assessed and briefly described. Akodon montensis often used fallen logs, lianas and ferns as climbing supports for movements. The species moved under different environmental structures with differing frequencies, with greater use of dense litter followed by lianas and fallen branches. The studied sigmodontine species used shelters of different compositions and structures, and differed in displacement behavior. This study is the first to contribute to understanding the movement and use of environmental structures, shelters and climbing supports by A. montensis.