Colonial Birds Nesting on Man-Made and Natural Sites in the U.S. Great Lakes
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Scharf, William C.
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Habitats and nesting populations of colonial nesting birds of the U. S. Great Lakes were determined by aerial census, ground nest observations, and vegetation analysis during 1976 and 1977. Thirteen species at 267 colonies were found during this 2-year study. An atlas of nesting sites and popula¬tions for both years of the study locates and gives the sizes of the colonies. Intensive vegetation and habitat studies were performed on 24 sites: 8 natural islands and 16 dredged material locations. A greater percentage of cover by herbaceous vegetation was favored by ring-billed gulls and herring gulls, but common and Caspian terns preferred less vegetative cover. Both ciconiiform and larid colonial nesters killed or badly stressed the vegetation supporting, sur¬rounding, and/or below their nests. Soil analyses showed high levels of macro-nutrients in most colonies except those of Caspian and common terns. These nutrients were presumed to be toxic except to a few adapted plant species fre¬quently found in heavily fertilized ring-billed gull colonies. The drop in Great Lakes water levels in 1977 produced new nesting sites and more nesting area. New colonies frequently had retarded nesting in relation to other colo¬nies and lessened intracolony synchrony, nest density, and nesting success. This was regardless of whether the site was natural or dredged material in origin. Colony size and previous experience of the breeders seemed more important , than latitude in determining date of peak hatching and chronological sequence of nesting in ring-billed gulls. The water table at the site affected nesting success by changing vegetation from hydric to xeric seres. In the case of standing impounded water, it could be drained or dewatered to provide addi¬tional nesting space. Effective dewatering practices are important to the construction of dredged material sites where colonial nesting birds are desired. Other management considerations important for encouragement or discouragement of colonial bird use are the proximity and attractiveness to humans allowing intrusions, proximity to an aircraft hazard zone, prevention of access by predators, height of dikes, and initial cover seeding or plant establishment. Appendix A presents maps of the colonies in the study. Appendix B lists common and scientific names of plants discussed in this report. Appendix C gives the relative density, coverage, and frequency of plants in the sample area. Appendixes D and E discuss the colonial nesting surveys in the St. Marys River area and the Beaver Islands archipelago, respectively.