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

Studies of the Common Loon, Gava immer, in eastern Canada and the United St ates suggest that the species' dependence on fish for food limits its breed ing habitat to large deep lakes with stocks of fish sufficient to support a dults and chicks. In central Alberta, breeding Common Loons are widespread, occurring on nutrient-rich lakes that vary in morphometry and prey base. F rom 1993 to 1997, small shallow lakes that were fishless (invertebrates wer e available as principal prey) or contained small-bodied fishes ("minnow la kes"), as well as larger deeper lakes containing large-bodied fishes ("pike lakes"), were surveyed to determine if the occurrence and breeding pattern s of Common Loons were influenced by prey assemblage and habitat type. Terr itorial pairs occurred on all three lake types, but nesting loons and fledg lings were more likely to be present on pike lakes than on fishless or minn ow lakes. Fishless lakes offered good nesting sites but chicks rarely fledg ed. Minnow lakes provided good chick-rearing conditions but loons did not o ften nest on these lakes.