Estimation of annual adult survival rates of Barnacle Geese Branta leucopsis using multiple resightings of marked individuals.

Accuracy and feasibility of three different methods to estimate adult annual survival rates in a migratory population of Barnacle Geese Branta leucopsis are examined. Estimates from resightings of birds marked with coloured leg-rings prve to be the more accurate. Bothe estimates derived from recoveries of metal-ringed birds, and those based on counts and age-ratio assessments are less accurate, particularly on an annual basis. The proportion of birds recovered is 4.3% for metal-ringed, and 99.1% for colour-ringed birds. The mean annual resighting reate of the colour-ringed birds is 80.5%. Underlying assumptions to estimate survival rates from such resightings are examined. Inequality between individual birds in the probability to be reported and ring loss cause underestimation of the survival rate. Misreading of the inscription on the rings may lead to an overestimation of the survival rate in one year, followed by an underestimation in a later year. In all, the estimated annual survival rate of 0.90 for adults seems to be slightly conservative. The effect of sex, age, and year on survival is examined.

Ebbinge B.S., Van Biezen J.B. & Van der Voet H., ARDEA 79 (1): 73-112.