General Ecology of a Rural Population of Norway Rats (Rattus norvegicus) Based on Intensive Live Trapping

We used intensive live trapping over a 1-y period to investigate the general ecology of a population of Norway rats (Rattus norvegicus) inhabiting a barn in east-central Illinois. At the start of our study in April 1986, the population contained 10 adult females and three adult males. The population increased and exhibited two peaks of about 100 individuals, one peak in late June and the other in late October 1986. Reproduction ceased during the late autumn and winter, and the population declined to only one adult male and one adult female by spring 1987. Increases in the number of rats represented young born at the barn, not adult rats moving into the population; decreases in population size likely resulted from predation rather than dispersal. Females first captured as adults persisted longer at the barn than did males and females first captured as juveniles or subadults; the few males first captured as adults persisted the shortest time of all age and sex classes. Young males gained body mass more rapidly than did young females. Wounding and parasitism by botflies occurred at relatively low levels. Our data indicate that a rat population with negligible immigration and seasonal breeding can exhibit dramatic changes in numbers, and that live-trapping at weekly intervals can yield high recapture rates useful for examining growth rates, survival and other basic life history characteristics.