Bridgman, G.K. 1998. Waterbird predation at four northern Minnesota aquaculture sites. M.S. Thesis, Bemidji State University. 22 pp.
Aquaculturists perceive some waterbird species to be a major economic threat to their livelihood, because rearing ponds offer a concentrated and convenient food source. We determined presence of waterbird species and seasonal and diurnal time activity budgets for the more common waterbirds at four northern Minnesota aquaculture facilities from 27 May to 4 November 1996. Thirteen waterbird species used the facilities; however, only Doublecrested Cormorants (Phalacrocorax auritis), Red necked Grebes (Podiceps grisegena) and Common Loons (Gavia immer) were considered common. Seasonal time activity budgets indicated that all species spent much of their time resting (36.0% - 82.5%). No seasonal differences in feeding were noted for cormorants and grebes, whereas loons fed more in the early season. Diumal time activity budgets indicated that cormorants fed more during the early morning, whereas loons fed more during the late morning, but only in the late season. Feeding activity by grebes did not differ by time of day. The low densities of cormorants at our study sites may suggest that they are more of a perceived threat for aquaculturists, though selective tree removal next to aquaculture sites may reduce any potential problems. Grebes, with low densities and little time allocated to feeding, are probably an unimportant waterbird predator. More loon research is needed to determine the extent of their damage at aquaculture facilities.