Common Loon Habitat Model
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Draft Date:
March 2001

Common loon, Gavia immer

Use of Study Area Resources:
Reproduction and wintering. Common loons breed throughout Canada, south into the U.S. Pacific Northwest, Great Lakes, and the Northeast. They winter on both coasts of the U.S., south into Mexico. Within the study area common loons breed on lakes, ponds and rivers of Maine and New Hampshire. They winter on coastal waters of Maine, New Hampshire and Massachusetts (McIntyre and Barr 1997, TASL 2000 web site).

Habitat Requirements:
Nesting Habitat. Common loons generally select clear, oligotrophic lakes with convoluted, deeply indented shorelines having multiple bays and numerous islands surrounded by boreal or mixed forest (McIntyre and Barr 1997). Loons nest on the ground or on floating mats of vegetation and, because they are awkward on land, they prefer nest sites at the water's edge with a steep drop-off that enables them to slip into the water (McIntyre and Barr 1997).  Additional preferences are protection from prevailing winds, and waves, some overhead vegetation or lateral cover, and a wide-angle (>130) vista of their territory (McIntyre and Barr 1997). Gibbs et al. (1991) found that loons in Maine preferred wetlands with relatively extensive open water. Sites having 52% in open water were used, while those with only 33% were not used. Loons locate prey visually by peering underwater, and diving in pursuit; they generally need at least 3-4 m of underwater visibility (McIntyre 1988), and feed primarily in clear waters in the littoral zone up to 5 m deep (McIntyre and Barr 1997). Prey items include saltwater and freshwater fishes, frogs, newts, snails, insects, insect larvae, crayfish, crabs, shrimp, amphipods, and lobsters (Creaser et al. 1993).

Nesting loons in Minnesota typically required lakes of 20 ha or larger, but occasionally lakes as small as 5 or 6 ha were used; large lakes could support multiple loon pairs, but lakes 80 ha or less typically supported only one pair (McIntyre 1975, 1988). Kerekes (1992) found that loons in southwest Nova Scotia, where lake productivity is poor and prey are scarce, required a minimum lake size of 40 ha. McNichol and Mallory (2000) found large lake size and the associated food supply to be the single most important factor in higher rates of reproductive success. Gibbs et al. (1991) found that in Maine loons did not occur in lakes having 7 ha of open water, but did occur in wetlands with 10 ha or more of open water.

Shoreline development and its associated human activity varies in its impact on loons. A study in southern Ontario (Heimberger et al.1983) found that when cottages were located within 150 m of a nest there was only a 45% chance of a successful hatch, whereas if development, with its associated human activity and boats were farther away, the success rate rose to 74%. Loons clearly avoided nesting where there were five or more cottages within 150 m.

Wintering Habitat. Loons use coastal waters including bays, coves, channels, inlets, and other shallow areas (Rimmer 1992, McIntyre and Barr 1997). Winter foods include flounder (Pleuronectoidei), rock cod (Gadus morhua), menhaden (Brevoortia patronus), salmonids, sculpin (Leptocottus armatus), and crabs. Maintenance activities (preening, drifting) usually take place in deeper water (McIntyre 1986, Daub 1989). Haney (1990) found that wintering loons selected areas up to 19 m in depth for feeding, and that few loons used waters greater than 20 m or further than 100 km from shore. They typically feed in the upper 5 m of the water column (McIntyre and Barr 1997).

Mapping and Habitat Model:
Inland Habitats. We obtained loon survey data for lakes in Maine (Florida Power and Light, courtesy of William Hansen; Loon Survey Database, 1983-1998, Maine Audubon Society, courtesy of Susan Hitchcox and Rob Bryan, and from Dave Evers), and for New Hampshire (Andrew Major, USFWS and Bob Estabrook, New Hampshire DES). These were used directly to map loon habitats, and were used in developing a model to identify potential inland habitats.

The loon inland habitat model relied on environmental parameters (lake trophic state, depth, area) propounded in the literature, in particular those used in loon habitat models by Gibbs et al. (1991). We obtained two data sets having environmental records, one for Maine (MDIF&W Lake Survey, 1990, courtesy of Owen Fenderson) and one extending into New Hampshire (Water Quality Parameters for Lakes, Ponds and Reservoirs in Maine and New Hampshire, ENSR, courtesy of Isabelle Morin). We tested the association of this database information with occurrence or absence of loons in Maine Lakes. The MDIF&W data were linked to 393 lakes surveyed for loons. The ENSR data linked to 254 lakes, all in common with the MDIF&W data. A combination of parameters from the 2 data sets (oligotrophic to mesotrophic conditions or average depth > 10', and area > 40 ha) gave correct classification rates of 79% for used lakes and 80% for unused lakes.

Lakes known to be used for breeding were given a habitat suitability score of 1.0; lakes with occasional loon occurrences, but not known breeding were given a score of 0.7; lakes offering potential habitat based on our model were scored 0.5.

Coastal Habitats. Wintering habitats were modeled from water depth and occurrence information in coastal (estuarine, marine, and tidal riverine) areas.  Water depths between +1 and -5 m in depth, mlw, were regarded as optimal (1.0); depths between -5 and -19 m were scored as suitable (0.5).  Where coastal areas were observed to be used by loons (based on MDIFW coastal wildlife surveys) the habitat score was made equal to the depth suitability (1.0 or 0.5). If loons were not observed the foraging habitat value was reduced to 0.2 and 0.1, respectively.

Model testing:
The model for inland habitat was tested by comparing the number of lakes actually used by loons and so identified by the model to the proportion that would have been identified by a chance selection process. The model identified 272 of 346 correctly, significantly better than the 173 expected by random selection. Also, all of the 54 lakes in New Hampshire identified by the model as potential habitat were subsequently found to be used by loons.

Creaser, E.P., H.C. Perkins and F. Pierce. 1993. Common loons feeding on lobsters. Maine Naturalist 1(4):223-224.

Gibbs, J.P., J.R. Longcore, D.G. McAuley and J.K. Ringleman. 1991. Use of wetland habitats by selected nongame water birds in Maine. USFWS Fish Wildl. Res. 9. 57 pp.

Haney, J.C. 1990. Winter habitat of common loons on the continental shelf of the southeastern United States. Wilson Bulletin 102(2):253-263.

Heimberger, M., D. Euler and J. Barr 1983. The impact of cottage development on common loon reproductive success in central Ontario. Wilson Bulletin 95(3):431-439.

Kerekes, J. 1992. The common loon in Nova Scotia Dept of Natural Resources: Conservation, Vol 16:2&3, downloaded 2.1.2000 from

McIntyre, J.W. 1978. Wintering behavior of common loons. Auk 95:396-403.

McIntyre, J.W. 1983. Pre-migratory behavior of common loons on the autumn staging grounds. Wilson Bulletin 95(1):121-125.

McIntyre, J.W. 1988.  The common loon: spirit of northern lakes. University of Minnesota Press. 229 pp.

McIntyre, J.W. and J.F. Barr. 1997. Common loon, Gavia immer. In A. Poole and F. Gill, (eds.) The Birds of North America, 313. Acad. Nat. Sci. Phil. and Amer. Ornith. Union, Washington D.C.

McNicol, D. and M. Mallory. Effects of lake acidity on common loon reproduction in Ontario from Canadian Lakes Loon Survey downloaded 2.1.2000 from

Rimmer, C.C. 1992. Common loon in Schneider and Pence (eds.) Migratory Nongame Birds of Management Concern in the Northeast. USFWS, Region 5, Hadley, Massachusetts. pp. 3-30.

Safina, C. 1997. Song for the Blue Ocean: encounters along the world's coasts and beneath the seas. Henry Holt and Co. 384 pp.

Strong, P.I.V. 1985. Habitat selection by common loons. PhD. thesis. University of Maine, Orono.

TASL (Take A Second Look) Online website: winter census data for Boston Harbor downloaded 2.18.2000.