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• <br />1 <br />Great Blue Heron and Great Egret Feeding Habitat, 1998 <br />Christine M. Custer <br />USGS, Biological Resources Division <br />Upper Midwest Environmental Sciences Center <br />P.O. Box 818 <br />La Crosse, WI 54602 <br />Final Report to Minnesota Department of Natural Resources <br />Introduction <br />Populations of both great blue herons (Ardea herodias) and great egrets (Casmerodius <br />albus) have declined in the Midwest and along the upper Mississippi River (UMR) (Thompson <br />1977, 1978a). It has been hypothesized that these population declines have been a result of <br />habitat quality changes including loss of nesting trees due to logging and flooding, and <br />degradation and loss of wetlands which has reduced the quality and quantity of feeding habitats. <br />Quality feeding habitat in proximity to breeding rookeries is an important aspect governing <br />reproductive success of colonial waterbirds. Quality habitat is defined around physical, biological, <br />and anthropogenic parameters such as water depth '(Custer and Osborn 1978), turbidity (Krebs <br />1974), vegetation characteristics (Thompson 1978b), food abundance, distance from breeding site <br />(Gibbs 1991), distance from human disturbance (Miller 1943), volume of barge and recreational <br />boat traffic, etc. Flooding, construction of dams, and dredging can alter the presence and location <br />of preferred feeding habitats in river system and thereby impact reproductive success. Urban <br />sprawl and wetland loss can also alter the location and quality of feeding habitat in other <br />situations. The objectives of this study were to determine the location of feeding habitat for great <br />blue hero ns and great egrets from selected rookeries (Fig. 1) and to quantify important habitat <br />features associated with those feeding sites. <br />Methods <br />• Using a single- engine, high- winged aircraft, the breeding rookery was circled in a counter- <br />