Philopatry and Nomadism: Contrasting Long-Term Movement Behavior and Population Dynamics of White Ibises and Wood Storks


We compare long-term movement behavior, breeding site philopatry, population dynamics and prey choice of White Ibises (Eudocimus albus) and Wood Storks (Mycteria americana) in order to illustrate (1) differences in strategies for exploiting spatially and temporally unpredictable food resources in wetlands of the southeastern U.S., and (2) the temporal and geographic scale at which conservation strategies for these species must be targeted. Since the 1930s, the U.S. White Ibis population has made a series of long-range (textgreater400 km) shifts in the center of its breeding range. Very large colonies seem to exist for less than 15 years, and to be supported by at least 800 km$^textrm2$ of wetlands. Movements may be prompted either by degrading breeding conditions caused by both man-made and natural disturbances, or by attraction to abnormally high concentrations of prey. Wood Storks have also undergone large scale shifts in the center of breeding, but are much more philopatric to breeding sites (often textgreater25 yr). They may be locally buffered from the unpredictability of food resources by the ability to forage at large distances from their colonies, and by being associated with more permanent wetlands. Preservation of specific colony sites and associated wetlands may well aid in conserving Wood Stork populations. In contrast, nomadic ibises require a different conservation approach, one that protects a geographically widespread network of wetland ecosystems.

Colonial Waterbirds