Many of the developments in mark-recapture methodology have been designed for open animal populations, with new animals entering through births and immigration and animals leaving through deaths and emigration. Studies usually involve sampling the population several times, with animals suitably marked when they are first captured so that they can be recognized when they are recaptured and a record obtained of the captures and recaptures of individual animals. Studies of open populations often cover extended time periods, and the population changes that occur are of great interest to ecologists and managers. Early methods for analyzing data from open populations were proposed by Jackson (1939, 1940, 1944, 1948), Fisher and Ford (1947), Leslie and Chitty (1951), and Leslie et al. (1953).