Efficient Estimation of Age-Specific Survival Rates from Ring Recovery Data of Birds Ringed as Young, Augmented by Field Information

Abstract

(1) Analysis of the survival of birds using recoveries from ringed nestlings depends on several assumptions and a constraint on the rate parameters (e.g. that mortality becomes constant after a certain age) and so is liable to be misleading. (2) The constraint can be avoided if the data are augmented by independent field evidence, e.g. monitoring a same-age group of birds by ring recoveries of birds of other known ages. (3) Age-specific survival rates estimated only from a mixture of ringed young and adults are unsatisfactory being based on the assumption that all adults have the same recovery and survival rates in a given year. This assumption may be untrue for most species, and its use is liable to distort the estimates of the rate parameters. (4) Ideally, to estimate age-specific survival rates, the age of every ringed bird should be known. I propose a scheme in which young and subadults are ringed in successive years. The estimation of the survival rates for older birds depends on constant recovery rate but no assumption is required for the young birds. (5) The ecological value of such an estimate and its improvement are discussed.