One hundred and twenty six months of live-trapping data, collected between 1994 and 2005, on 17 tree islands of the Everglades prairie, was used to describe the patterns of island occupancy, reproduction and movement of the two most common small mammal species in this habitat, the marsh rice rats (Oryzomys palustris) and the cotton rats (Sigmodon hispidus). Islands were categorized by size as large, medium and small. Cotton rats were captured in higher numbers than rice rats on large and medium islands. On small islands, rice rats had more than twice the captures of cotton rats. The proportion of rice rat captures, unlike the cotton rat, was not positively associated with island size. The largest proportion of captures occurred on large islands followed by small and medium size islands. The proportion of rice rat juvenile captures and the proportions of reproductively active individuals and subadults, for both rice rats and cotton rats, were not significantly different from the proportion of captures for all individuals on each island size class. However, the proportion of juvenile cotton rats was greater than the proportion of all captures on large islands and less than the proportion of all captures on small and medium size islands. The mean adult body weight of cotton rats, unlike that of rice rats, differs across islands with large islands having adults with a higher mean adult weight than adults in smaller islands. These results suggest that subordinate individuals are displaced to smaller islands where they produce fewer young and that the availability of large tree islands likely influence in situ recruitment of cotton rats. The presence or depth of water did not influence the movement rates of rice rats and, contrary to previous studies, the movement rates of cotton rats were not significantly influenced by the presence of water.