LOCAL RECRUITMENT IN THE GREATER-FLAMINGO - A NEW APPROACH USING CAPTURE-MARK-RECAPTURE DATA

Although the establishment of new individuals in the breeding componen t of a population is an essential feature of population regulation, on ly a few attempts have been made to test biological hypotheses about r ecruitment. Most previous studies rely on ad hoc calculations or are f lawed with unwarranted assumptions about survival. We use a recently d eveloped approach, based on capture-mark-recapture, in which analysis of local recruitment is similar to a time-reversed analysis of surviva l. The basic data set consists of capture histories viewed in reverse order, with initial capture at year of birth, and subsequent observati ons corresponding to years when the animal has bred. The model conside rs two essential components, the probability for any breeding individu al to reproduce for the first time (beta, the probability of first rep roduction) and the probability of recapture (p), both conditional on s urvival. Contrary to previous attempts at modeling recruitment, the pr esent approach does not assume an age at which breeding propensity sta bilizes to a maximum value. The flexibility achieved allows the compar ison of recruitment among groups within a population and also allows o ne to consider the effects of environmental variables, as well as inte ractions between such effects. Practically, the procedure starts from a global model, based upon the a priori knowledge of the biology of th e species, and assesses its fit. Then more parsimonious models are sel ected using Akaike's Information Criterion and likelihood ratio tests. Finally, maximum likelihood estimates of model parameters are obtaine d with estimates of precision. We used a modified version of program R ELEASE for goodness-of-fit tests, and program SURGE for iterative mode l fitting and the computation of likelihood ratio tests. We illustrate the method with the study of local recruitment of Greater Flamingos ( Phoenicopterus ruber resells) in the Camargue (southern France) betwee n 1984 and 1994. We found additive effects of age and year to affect r ecruitment. Breeding propensity increased with age. Recruitment was no ticeably higher in the year following an increase in mortality rate du e to a particularly severe winter. Longlasting effects of this increas ed mortality on recruitment were observed in the three following years . There was no evidence for an effect of sex or cohort (year of birth) on recruitment. However, sex, as well as time and age, affected recap ture rates. We discuss the various advantages and limitations of the m odel for the study of local recruitment in long-lived species and ment ion some potential developments.