DETERMINANTS OF THE SIZE AND LOCATION OF GREAT BLUE HERON COLONIES

We integrated habitat information over a range of spatial scales for G reat Blue Herons (Ardea herodias) nesting in Illinois, U.S.A., to iden tify key habitat factors associated with the location and size of nest ing colonies. Availability of lacustrine and emergent wetland was the primary determinant of which regions Great Blue Herons established col onies. Within such regions, the herons located their colonies near loc al concentrations of wetland and centrally to regional wetland complex es. Herons settled among colonies in numbers proportional to the avail ability of foraging habitats near colony sites. Colonies were located at sires with more buffering habitat (forest, swamp, and open wetland) and lower road density, and within larger forest stands, than expecte d at random. Characteristics of vegetation used for nesting varied str ikingly among nearby colonies. A hierarchical model of habitat selecti on may be useful for explaining distributional patterns of nesting Gre at Blue Herons.