Where do common loons breed?

The common loon (Gavia immer) is a large diving bird found across North America. It breeds on lakes in Canada and the northern United States before migrating south for the winter. Common loons have iconic black-and-white plumage and are known for their eerie, haunting calls. Understanding where common loons breed is important for conservation efforts to protect their breeding habitat.

Breeding Range

Common loons breed across Canada and Alaska, as well as in the northern United States from Washington to Maine. Their breeding range extends as far north as the treeline in Canada and Alaska. Key breeding states include:

• Minnesota
• Wisconsin
• Michigan
• New York
• Vermont
• New Hampshire
• Maine

Some isolated breeding populations may also occur further south along the Appalachian Mountains. The core of the common loon’s breeding range is centered on Canada, where it is estimated over 80% of the global population breeds.

Breeding Habitat

Common loons require lakes for breeding. They nest very close to shorelines, preferring quiet bays and sheltered inlets. Ideal breeding lakes are clear, oligotrophic lakes with rocky shorelines and scattered islands. The lakes must be large enough to support breeding territories and have an abundant population of small fish to sustain the loons.

Typical characteristics of prime common loon breeding lakes include:

• Size – Over 6 hectares (15 acres) in size
• Depth – Deep enough so fish can escape winter freeze (at least 4-5 m)
• Water quality – Clear water with low turbidity
• Fish populations – Abundant small fish such as minnows, sunfish, and perch
• Shoreline – Gradual slope with mix of rocks, gravel, and sand
• Vegetation – Emergent plants along shoreline for nesting
• Human disturbance – Low level of human activity on the lake

The common loon is highly sensitive to human disturbance and will abandon nesting territories if disturbance levels are too high. Quiet wilderness lakes provide the best breeding sites.

Territory Size

Common loons are territorial and require adequate space on breeding lakes. Each breeding pair establishes a territory that can range from 8 to 200 hectares in size, with an average size of about 40 hectares. Territory size tends to increase at higher latitudes.

The size of the territory is influenced by factors such as lake size, shoreline complexity, and food availability. Larger territories are required when food resources are limited. Territories include both nesting and foraging areas along the lake shoreline.

Common loons show high fidelity to their breeding territories. Pairs will often return to the same territory year after year if conditions remain favorable. Aggressive encounters may occur along territory boundaries.

Nesting

Nest site selection is a critical factor in common loon breeding success. Ideal nest sites provide safety from land predators and minimize the chances of flooding. Common loon nest sites have some typical characteristics:

• Location – Close to water, usually within 3 meters of shoreline
• Land cover – Small islands, emergent vegetation clumps, muskrat houses
• Substrate – Mats of dead vegetation over muddy ground or sand
• Concealment – Nest bowl concealed by overhanging vegetation
• Elevation – Above waterline to avoid flooding

Nests are simple scrapes or bowls built from available vegetation and lined with down from the parent’s breast. Nest building begins shortly after the spring thaw when the lakes become ice-free.

Clutch Size

The typical common loon clutch size is two eggs. The eggs are large, elliptical, and olive to brownish-black in color with dark brown speckles. Egg laying begins in late May or early June, with eggs laid at 1-2 day intervals.

Both parents incubate the eggs for 27-29 days before hatching. Loon chicks are precocial and able to swim and dive soon after hatching. Parents will care for the young for the first 8-10 weeks until they fledge and become independent.

Larger clutch sizes of 3-4 eggs may occasionally occur but increase the risk of predation. Two egg clutches are most productive for healthy loon populations.

Threats on the Breeding Grounds

Common loons face a number of threats on their northern breeding lakes, including:

• Shoreline development – Cottages, marinas, boat traffic can displace birds
• Recreational use – Boats, personal watercraft cause wakes/disturbance
• Pollution – Oil spills, fuel leaks, runoff of lawn chemicals
• Fishing gear entanglement – Discarded fishing lines trap/drown loons
• Predators – Gulls, crows, mink, raccoons, bald eagles may eat eggs
• Climate change – Changing water levels, temperatures, ice cover patterns

Conservation programs across the breeding range aim to protect key habitat, limit human disturbance, and monitor threats. Continued stewardship of northern lakes will be critical to ensure loon populations remain stable.

Breeding Populations

The North American common loon population is estimated at 450,000-500,000 adults. Of these, an estimated 380,000 breed in Canada. Key provincial breeding populations include:

In the United States, key breeding states include:

Breeding Density

The density of breeding common loon pairs varies across their range, with highest densities in core boreal habitat. Some typical breeding densities include:

• Boreal forest lakes in Canada – 2.2 to 4.5 pairs per 100 km2
• Northern forest lakes in Maine – 1 to 2 pairs per 100 km2
• Adirondack lakes in New York – 0.15 to 0.48 pairs per 100 km2
• Lakes in Michigan – 0.18 to 0.35 pairs per 100 km2

Higher breeding densities tend to correlate with higher territory quality and food availability. As habitat quality declines, density and reproductive success also decline. Maintaining high quality breeding lakes is key for robust loon populations.

Breeding Synchrony

Common loons tend to nest in a synchronous manner across different lakes in a given region. This means breeding activity becomes concentrated into a few weeks each spring.

Nesting synchrony likely helps reduce egg and chick predation. When many loons are nesting simultaneously, predators cannot focus on a single lake. Synchrony may also assist with mate replacement if a nest fails early in the season.

Weather factors like ice-out timing, temperature, and precipitation help cue nesting activity each spring. Loons navigate a narrow spring window to match food availability to chick rearing.

Population Trends

Over the past 40 years, common loon populations appear to be stable and increasing across parts of their breeding range. Stewardship programs and protection of boreal lakes have aided loon conservation.

However, in parts of the U.S. northeast and midwest, breeding numbers are declining. Threats on migration and wintering areas may contribute to these regional declines. Continued monitoring is needed to conserve vulnerable populations.

Targeted conservation programs through partnerships like the Canadian Lakes Loon Survey and the Minnesota Loon Monitoring Program are crucial for tracking loon population health over time. Maintaining high quality breeding habitat remains the key factor for common loon conservation.

Conclusion

In summary, common loons rely on clear, quiet lakes across Canada and the northern U.S. for breeding. Nesting on islands and vegetation mats, loon pairs establish territories and raise small clutches of precocial chicks. Breeding loons face threats from human disturbance and habitat degradation. Stewardship of northern lakes maintains vital breeding habitat for loons. Tracking populations and breeding success ensures robust populations of this iconic northern diver. With mindful management of their wilderness breeding lakes, the haunting cry of the common loon will continue echoing across northern forests for generations to come.