Estimating the size of a transient population

Migratory populations often stop over for short periods of time at predicta ble sites along their migration routes. These staging areas can be heavily used and are potentially critical to the survival of the migrants. This pap er presents a method for estimating the number of individuals using such an area and their average residence time. The estimator is based an daily pop ulation estimates and records of repeat sightings of identifiable individua ls. Its application is illustrated with observations on a population of mig rating birds, some of which could be identified from bands that were readab le from a distance.