Bioacoustics of Rattus rattus

Movements, Home range and Social organization. In an old growth riparian forest in California, Roof Rats nested in trees 2-15 m above the ground, although most were located in burrows underground. Males moved 38 m/h at night; females moved 27 m/h. Home ranges were 0-22-1-9 ha, although in more urban areas, they would be much smaller because of lack of space and barriers caused by buildings and other man-made structures. Home ranges ofall individuals overlapped, regardless of sex. Nesting can be communally with many individuals in a single large nest, or an individual in a small nest. A recent study found that when Roof Rats are deprived of food, they socialize and share rather than fight. Cooperative behavior is a result of their hierarchal social structure in large nests with more dominant individuals. Nevertheless, fighting is common, and there can be a lack of cooperative behavior among members of a group, which leads to most individuals ignoring each other except when mating or sleeping as a group in the nest. Dominance plays an important role in population regulation because relative dominance in a group hierarchy determines access to resources and mates. Larger individuals tend to be more dominant because they can overpower other individuals. Density is highest in late summer and early autumn. Roof Rats and Brown Rats ( R. norvegicus ) are cautious yet inquisitive. Exploration is common, but both species can be neophobic toward food and other objects; individuals will cautiously approach and smell or touch an unfamiliar object and then dart away quickly. Dispersal distances from nests are generally very short, with individuals usually staying close to their natal nests. In cases of extreme environmental pressure, Roof Rats will move further away from their original nest sites and can make new nests. A study of a semi-natural large nest of Roof Rats found that they made ten distinct acoustic signals, five of which were ultrasonic. Although the utility of these signals is unknown, they probably aid in intraspecific communication.