Breeding patterns of Common Loons on lakes with three different fish assemblages in north-central Alberta

Studies of the Common Loon, Gavia immer, in eastern Canada and the United States suggest that the species' dependence on fish for food limits its breeding habitat to large deep lakes with stocks of fish sufficient to support adults and chicks. In central Alberta, breeding Common Loons are widespread, occurring on nutrient-rich lakes that vary in morphometry and prey base. From 1993 to 1997, small shallow lakes that were fishless (invertebrates were available as principal prey) or contained small-bodied fishes ("minnow lakes"), as well as larger deeper lakes containing large-bodied fishes ("pike lakes"), were surveyed to determine if the occurrence and breeding patterns of Common Loons were influenced by prey assemblage and habitat type. Territorial pairs occurred on all three lake types, but nesting loons and fledglings were more likely to be present on pike lakes than on fishless or minnow lakes. Fishless lakes offered good nesting sites but chicks rarely fledged. Minnow lakes provided good chick-rearing conditions but loons did not often nest on these lakes.