IMPORTANCE OF LANDSCAPE HETEROGENEITY TO WOOD STORKS IN FLORIDA EVERGLADES

Declines in populations of and reproductive success of wood storks and other wading birds have occurred in the Florida Everglades over the p ast several decades. These declines have been concurrent with major ch anges in the Everglades' landscape characteristics. Among the plausibl e hypotheses that relate to landscape change are the following: (1) ge neral loss of habitat; (2) heavy loss of specific habitat, namely, sho rt-hydroperiod wetlands that provide high prey availability early in t he breeding season; and (3) an increase in frequency of major drying o ut of the central slough areas, which can affect prey availability lat e in the breeding season. These three hypotheses were compared using a n individual-based model of wood stork (Mycteria americana) reproducti on. This model simulated the behavior and energetics of each individua l wood stork in a breeding colony on 15-min time intervals. Changes in water depth and prey availability occurred on daily time steps. Simul ation results showed a threshold response in reproductive success to r eduction of wetland heterogeneity. Model comparisons in which (1) only short-hydroperiod wetlands were removed and (2) wetlands of both long and short hydroperiods were removed showed that, for the same loss of total area, the specific habitat removal caused a much greater reduct ion in wood stork reproduction, indicating hypothesis 2 may be a more likely explanation than hypothesis 1. Reduction of initial prey availa bility in the central slough areas (simulating frequent drying; hypoth esis 3) reduced fledging success by an average of more than 90% in the model.