Habitat

Common Loon breeding habitat, Alaska.

Breeding Range

Prefers lakes larger than 24 ha with clear water, an abundance of small fish, numerous small islands, and an irregular shoreline that creates coves; however, uses a wide variety of freshwater aquatic habitats, including reservoirs, even when water level fluctuations regularly vary to the extent of causing repeated nest failures. Rivers are not used for nesting habitat unless oxbow-like areas with minimal current are available. Also breeds on larger, deeper tundra lakes of sub-Arctic and Arctic North America, Greenland, and Iceland, where may be sympatric with Yellow-billed and Pacific loons.

Water quality is important for successful breeding. Loons are visual predators, so clear water is crucial for efficient foraging. A Michigan study found that the time adults spent foraging in turbid water was significantly greater than the time it took to forage in clear water (Gostomski and Evers 1998). At Secchi disk readings of ≤ 1.5 m, loons alter their foraging behavior (Barr 1986). Total suspended solid measurements at Seney National Wildlife Refuge in Michigan indicate that breeding loons prefer lakes with values below 28 Nephelometric Turbidity Units (NTU). Lakes over that NTU level were not used for nesting purposes (DCE). Further field efforts that can correlate breeding loon presence and success with water turbidity are needed.

Spring And Fall Migration

Few studies. Populations with short-distance overland movements from breeding to wintering areas do not use staging areas on a regular basis. Long-distance migrants need staging areas for rest, to replace lost body reserves, and to forage. An adequate staging area includes abundant prey and relatively clear water. Large lakes and rivers that meet these habitat requirements are used by interior migrants (McIntyre and Barr 1979, McIntyre and Barr 1983, Hertzel et al. 2000), while ocean-going migrants most likely use near-shore areas (Powers and Cherry 1983).

Winter Range

Wintering and non-breeding loons generally use habitat within inland coastal waters such as bays, channels, coves, and inlets; rarely occupy habitat more than several kilometers offshore (Lee 1987a, b, Haney 1990). The use of specific marine habitat is dictated primarily by prey availability, which is influenced by water depth, clarity and salinity gradients, and tide lines (McIntyre 1978, Lee 1987b, Haney 1990, Vlietstra 2000). Haney (1990) found that loons generally use waters up to approximately 40 m deep within 90 km of the shore; peak use occurred in areas less than 20 m deep. Loons generally avoid areas with highly turbid water, such as the mouths of rivers, because these limit foraging success (Daub 1989, Haney 1990, Jodice 1993). Seasonal, spatial, and annual variability is due to shifting abundance of small fish (Ford and Gieg 1995, Spitzer 1995).

Interior freshwater areas such as reservoirs in the southern U.S. and large slow-moving rivers are commonly used as wintering habitat, but their use is greatly influenced by weather. Even though the southern Great Lakes usually remain open through the winter, loons are relatively rare and those that attempt to over-winter are often physically compromised and unable to complete the migration (DCE).