Population dynamics of small songbirds are driven in part by fecundity and productivity (i.e., the number of young that fledge and survive the dependent stage, respectively, per adult female per year). Because of the challenges of obtaining empirical estimates for productivity or fecundity, some researchers predict fecundity using a three-factor model or more complex models such as those developed by Pease and Grzybowski (1995) or Farnsworth and Simons (2001, 2005). All these models generate a single prediction with no estimate of variability around the prediction. We developed an individual-based model that provides predictions of productivity and measurements of variability surrounding the predictions for simulated populations of Louisiana Waterthrushes (Seiurus motacilla) based on various aspects of their breeding cycle. Our empirical estimate of productivity in Louisiana Waterthrush (x̄ ± SD = 1.50 ± 1.45) was similar to that provided by our individual-based model (1.07 ± 1.24). On the basis of our model, productivity was most sensitive to and increased dramatically with increasing fledgling survival, daily nest survival, followed by nestling survival. The remaining four factors had weak, if any, effects on productivity. When compared with our individual-based model, the three-factor and Pease and Grzybowski (1995) models often produced higher predictions of fecundity, ≤2.1 additional young fledged per female. This is likely attributable to the addition of a renesting rate in our individual-based model. The Farnsworth and Simons model often produced predictions that were similar to those from our individual-based model. We believe that our individual-based model is an improvement over most existing songbird-fecundity models and can be generalized to accommodate other breeding factors, including brood parasitism and temporal variability.
¿Cuáles Componentes de la Historia de Vida Determinan la Productividad Reproductiva Individual en las Aves Canoras? Un Estudio de Caso con Seiurus motacilla