Abstract
Many species only show sexual dimorphism at the age of maturity, such that juveniles typically resemble females. Under these circumstances, estimating accurate ageâspecific demographic parameters is challenging. Here, we propose a multievent model parameterization able to estimate ageâdependent survival using captureârecapture data with uncertainty in age and sex assignment of individuals. We illustrate this modeling approach with captureârecapture data from the ringânecked parakeet Psittacula krameri. We analyzed capture, recapture, and resighting data (439 recaptures/resightings) of 156 ringânecked parakeets tagged with neck collars in Barcelona city from 2003 to 2016 to estimate the juvenile and adult survival rate. Our models successfully estimated the survival probabilities of the different age classes considered. Survival probability was similar between adults (0.83, 95% CI = 0.77â0.87) and juveniles during their second (0.79, 95% CI = 0.58â0.87) and third winter (0.83, 95% CI = 0.65â0.88). The youngest juveniles (1st winter) showed a slightly lower survival (0.57, 95% CI = 0.37â0.79). Among adults, females showed a slightly higher survival than males (0.87, 95% CI = 0.78â0.93; and 0.80, 95% CI = 0.73â0.86, respectively). These high survival figures predict high population persistence in this species and urge management policies. The analysis also stresses the usefulness of multievent models to estimate juvenile survival when age cannot be fully ascertained.
Highlights
Many life history processes and parameters are age-Âdependent (Roff, 1992; Stearns, 1992)
The aim of this study is twofold: (a) to provide a multievent model approach to overcome the problem, typical to many species, of uncertainty in age and sex determination of individuals when estimating age-Âdependent survival probabilities; and (b) to provide estimates of age-Âdependent survival rates for the ring-Ânecked parakeet, which can be of use in population dynamics and viability models, essential to evaluating the risks of invasion of this species (Pruett-ÂJones, Newman, Newman, Avery, & Lindsay, 2007)
We show, for the first time, that the method can be extended to estimate age-Âspecific survival rates when age cannot be fully ascertained
Summary
Many life history processes and parameters are age-Âdependent (e.g., age at maturity, age-Âspecific survival, or age-Âspecific reproductive investment) (Roff, 1992; Stearns, 1992). The age of an individual is a key ecological parameter in population dynamics studies (Cam, 2009; Perrins, Lebreton, & Hirons, 1991; Sutherland, 1996; Williams, Nichols, & Conroy, 2002). A general approach for studying age-Âand sex-Âspecific population dynamics parameters in these species is to consider only the individuals for which age and sex have been determined with.
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