Individual based models of avian wildlife populations

An individual-based simulation modeling approach was used in an effort to predict reproductive success of two species of colonially nesting wading birds: the Great Blue Heron (Ardea herodias) and the Wood Stork (Mycteria americana). Two totally different problems were looked upon using the approach. First, the effects of the alteration of foraging conditions for the two species in the Everglades area were considered. The models used for each species followed simultaneously daily activities of individual birds, their spatial movements, foraging efficiency, bioenergetics and growth of the nestlings during a nesting season. For each of the models the effects of reversals were looked upon (that is, increases in depth during the dry season when water levels are normally falling) as a factor affecting reproductive success. Species-specific differences such as visual feeding (for the Great Blue Heron) and tactile feeding (for the Wood Stork were implemented in the models. Simulation results showed that the Wood Storks, frequently foraging in groups, were more affected by the introduced resource scarcity, mainly because of rapid depletion of concentrated resources. Second, the effects of PCB bioaccumulation were studied in a colony of Great Blue Herons. The model considered spatial distributions of PCBs in fish in the colony area. Individual birds were followed and their PCB uptake, bioaccumulation, and retention were modeled. Behavioral responses (foraging deficiency, flight speed) were taking into account using dose-response functions. Simulation results showed that the sublethal behavioral responses in many cases can determine the success of the colony.