A Preliminary Model of Wood Stork Population Dynamics in the Southeastern United States


We modeled population dynamics and extinction probabilities for the endangered Wood Stork (Mycteria americana) using count data from synoptic aerial surveys, annual measures of productivity from throughout the southeastern U.S., and survival data from satellite-tagged juveniles. Using a simple, count-based diffusion approximation approach we were able to quantify an increasing population trend since 1976. High inter-year variability resulted in wide confidence intervals and we could not eliminate the possibility of long-term population decline in spite of recently measured population increases. We also used a stage-based population matrix model to incorporate observed differences in survival rates among age classes. Fledging success, and survival of fledglings, one, and two-year-old birds were estimated using data from the satellite telemetry study. Because the survival rates of three-year-olds and adults are presently unknown, we analyzed population dynamics over a range of these values. Long-term population growth was most sensitive to changes in adult survivorship. This deterministic matrix model indicated that adult survival rates textgreater0.94 were necessary to maintain a growing population, an estimate considerably higher than that observed in the European White Stork (Ciconia ciconia). This study underscores the need for reliable estimates of juvenile and adult survival in Wood Storks, and for a conservation focus on the factors that affect adult survival. It also provides a tool for understanding and projecting potential trajectories of the Wood Stork population in the Southeastern United States.