Loon Ecology

Annual Cycle or Phenology

Phenology is the study of periodic biological phenomena, such as flowering, breeding, and migration, especially as related to climatic conditions. Common Loons arrive on Wisconsin lakes as soon as the ice leaves in mid-to-late April. Most loons in Wisconsin are nesting by mid-to-late May, with eggs beginning to hatch one month later in mid-to-late June. Some pairs that begin nesting later, or who lose their first nest and try a second time, will have eggs hatching into early July. Loons typically lay only two eggs per nesting attempt. Nests with three and even four eggs have been documented, but are rare.

After chicks hatch, they stay on the nest for up to one day until the adults call them off. Once on the water, they are taken to a nursery area, which is usually a secluded bay or protected shoreline. Adult loons feed and protect the chicks until they can dive and catch their own food at approximately eight weeks of age. Adults often leave the chicks and form pre-migratory flocks in early August. Adults begin flying south in late August and early September. Chicks stay on the nesting lakes, feeding and taking their first test flights, until nearly ice-over. One day, they start running across the water, take flight, and head south, where they will stay until they are three years old. Most chicks return to their nesting lake (or one close by) when they have attained the adult’s black-and-white feathers at the age of three. However, current research is finding that many loons do not acquire a nesting territory until they are six years old, so most end up swimming around our lakes, waiting for an open territory.

Loon Breeding Habitat

Common Loons are widely distributed in northern Wisconsin and the Upper Midwest, but not all lakes have loons on them. While there are no criteria that guarantee a lake will have nesting loons, the following are important characteristics.

• Most lakes occupied by loons during the breeding season are found in the extensive forested landscapes of the Midwest. These areas are generally referred to as the Northwoods of Minnesota, Wisconsin, Michigan, and Canada.
• Loons are most often found on lakes fifty acres and smaller, but all sizes are used. Most loons need at least ten acres but they have been observed on lakes as small as two acres on rare occasions.
• Loons live on lakes of all different shapes, but generally a lake with an irregular shoreline is best. Lakes with an abundance of peninsulas, protected coves, and islands can often support more than one pair of nesting loons.
• Loons live on lakes with varying pH levels, but lakes with a pH of 4.5 or less often do not have loons due to low fish populations.
• Loons need clean, clear water because they search for fish by peering underwater from the surface. Lakes that have limited water clarity due to pollution, algae blooms, or the stirring up of bottom sediments generally are not good for loons.
• Water depth is believed to be of little importance to loons. Use of ponds approximately 1.5 feet deep has been documented.
• Some loons can tolerate, or become accustomed to shoreline development, but undisturbed shorelines are needed for nesting. As homes, resorts, marinas, and beaches surround a lake, it may become less suitable for loons.
• Loons can live alongside some human recreational activities, but they are vulnerable to direct harassment and recreational use near nests and nursery (chick-rearing) areas. Disturbance during critical times in the breeding season can cause unnecessary stress and lead to abandonment of nests and ultimately the lake.
• Loons can adjust to natural lake level changes, like increases after rainstorms and declines during dry spells. Large fluctuations caused by human activities, especially during the nesting season (May to July) can make a lake unsuitable for nesting loons.
• Loons build their nests at the water’s edge because they have difficulty walking on land. Loons prefer to nest on islands and in backwaters protected from wave action. Often, they use the same nest site each year.
• Nest sites are generally selected on undisturbed islands and stretches of lakeshores where native vegetation is present. They prefer to nest at the water’s edge of wetland communities such as sphagnum bogs, marshes, and mud flats. Loons generally avoid areas that have been converted to lawn and where human disturbance is a regular occurrence.
• Nests are constructed out of mud and whatever vegetation material is available. They will pull muck and decaying vegetation off the bottom of the lake to add to the nest. Occasionally nests will be crude with little material added and may resemble a type of nest called a scrape, a slight bowl-shaped depression in the ground with little material added.
• Also LoonWatch has information and building plans for Artificial Nesting Platforms.

Loon Wintering Habitat

In the fall, loons migrate south to spend the winter on the ocean along the Atlantic coast and the northern coast of the Gulf of Mexico. There they feed and molt in coastal areas and do travel some distance offshore. Little is known about the wintering ecology of loons and there are many questions we would like to have answers for such as: Do individuals return to the same wintering sites each year as they do on the breeding grounds? Do females and males use different sites? How does weather (and large storms like hurricanes) affect the winter distribution of loons? Do loons aggregate and, if so, where? Do loons select certain areas for specific resources?

Loon Migration Habitat

Common Loons frequently use lakes not used during the breeding season as stopover points during migration. These lakes are important as staging areas and as feeding and resting locations during migration. The Great Lakes and large inland lakes and reservoirs throughout the eastern US and Canada play an important role in maintaining the loon population. Without quality stopover sites, loons may have a difficult time traveling between their breeding grounds and their wintering sites on the Atlantic Ocean and Gulf of Mexico. Little is known about loon migratory habitat and therefore is an important subject for future studies.