Demographic Approach to Releasing Adults versus Young in Reintroductions

: Reintroductions are often used for reestablishment of animal populations. The choice of age-class of released individuals, however, is often arbitrary or based on expediency. We developed a demographic model that predicts the relative efficiency of releasing juveniles or adults for a given life cycle. The model accounts for possible reduction of survival and fertility of released adults. It also incorporates demographic and environmental stochasticity to compare release strategies of varying duration and number of releases. We applied the model to the case of reintroduction of Griffon Vultures (Gyps fulvus) in southern France, for which accurate monitoring allowed us to estimate demographic rates and consequences of releases. Overall, for Griffon Vultures, it is more efficient to release adults than juveniles, despite the observed reduction of demographic parameters following release. This approach could be used for the reintroduction of other species. Resumen: Las reintroducciones son frecuentemente utilizadas para el restablecimiento de poblaciones animales. Sin embargo, la eleccion de las clases de edad de los individuos liberados es frecuentemente arbitraria o basada en la conveniencia. Desarrollamos un modelo demografico que predice la eficiencia relativa de la liberacion tanto de juveniles como de adultos para un ciclo de vida determinado. El modelo toma en consideracion la posible reduccion de la supervivencia y fertilidad de los adultos liberados. Tambien incorpora parametros aleatorios demograficos y ambientales para comparar las estrategias de liberacion segun la duracion y el numero de liberaciones. Aplicamos este modelo en el caso de la reintroduccion del buitre leonado (Gyps fulvus) en el sur de Francia, para el cual un monitoreo preciso nos permitio estimar las tasas demograficas y las consecuencias de las liberaciones. En general, para el buitre leonado es mas eficiente liberar adultos que juveniles, a pesar de la reduccion observada de los parametros demograficos posteriormente a la liberacion. Esta aproximacion podria ser utilizada en la reintroduccion de otras especies.

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