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Common Loon Life History


Lakes and PondsCommon Loons are a classic bird of the North Woods lakes. They are excellent indicators of water quality as they require crystal-clear lakes (which makes it easier for them to see prey underwater) with abundant populations of small fish. Lakes with coves and islands are preferred as they provide cover from predators while resting and nesting. They also require lakes with enough surface area for their flapping-and-running takeoffs across the water. In their winter range along ocean coasts, they occur fairly close to shore and in bays and estuaries. They are only rarely found more than several miles offshore. Some Common Loons winter inland, on large reservoirs and slow-moving rivers. Common Loons that migrate across interior North America find large lakes and rivers to move between on their way north and south. Back to top


FishCommon Loons are expert anglers. Their diet consists of mostly fish, particularly perch and sunfish on their northern lakes. If fish are scarce or water is too murky for fishing, they will catch crustaceans, snails, leeches and even aquatic insect larvae. Though people on the surface only see loons disappear with a dive and reappear with a fish in their bill to be swallowed headfirst, their fishing pursuits underwater are something to behold. Loons shoot through the water like a torpedo, propelled by powerful thrusts of feet located near the rear of their body. When their quarry changes direction, loons can execute an abrupt flip-turn that would make Olympic swimmers jealous: they extend one foot laterally as a pivot brake and kick with the opposite foot to turn 180 degrees in a fraction of a second. In their wintering waters, loons eat smallish fish such as Atlantic croaker. Sometimes they band together in groups to chase schools of Gulf silversides. Back to top


Nest Placement

GroundThe male selects the nest site. Loons nest in quiet, protected, hidden spots of lakeshore, typically in the lee of islands or in a sheltered back bay. Loons can’t walk well on land, so nests are built close to a bank, often with a steep dropoff that allows the bird to approach the nest from underwater. They also use artificial nesting platforms, which people have offered as alternative habitat on lakes with extensive shoreline development. Many times a nesting pair of loons will reuse the same site the following year, refurbishing their old nest instead of building a new one.

Nest Description

Male and female build the nest together over the course of a week in May or early June, making a mound out of dead plant materials such as sedges and marsh grasses that grow along the lake’s edge. Then one of the loons crawls on top of the mound and shapes the interior to the contours of its body. The finished nest is about 22 inches wide and looks like a clump of dead grasses by the edge of the water.

Nesting Facts

Clutch Size:1-2 eggs
Number of Broods:1 brood
Egg Length:3.5-3.5 in (8.8-9 cm)
Egg Width:2.2-2.2 in (5.5-5.7 cm)
Incubation Period:26-29 days
Nestling Period:2 days
Egg Description:Brown with dark splotches.
Condition at Hatching:Covered with down, sooty black with a white belly. Able to swim and ride on parents’ backs within hours of hatching.
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Surface DiveCommon Loons spend a lot of their time working shallow waters for fish: swimming slowly and sticking their heads into the water to look for fish, then diving suddenly after their quarry with a quick plip! that hardly leaves a ripple on the water’s surface. Loons do all their feeding during the day, when they can best see their prey. At times, loons can be seen sticking one foot up out of the water and waggling it—this may be a means of cooling off, as scientists have observed loons waggling their feet more often on sunny, midsummer days. Loons also perform a territorial display of lifting their body upright and flapping their wings vigorously. Canoeists who get too close to a loon may witness this display, along with a defensive tremolo call as the loon swims away. Loons also tremolo when they fly from lake to lake or in circles above a lake, their necks sticking straight out and feet trailing behind them. They can be very vocally active with nocturnal choruses. After sundown, many North Woods lakes reverberate with the echoes of loon wails and yodels and tremolos (which writer John McPhee called “the laugh of the deeply insane”). In spring, loon mates arrive back on their lake separately. Loons are monogamous, and pair bonds typically last about 5 years. If one year one of the mates doesn’t return, the other will quickly pair up with another mate. The male defines his territory through yodeling. Courtship consists of swimming in circles and synchronous dives. If nesting is successful, loon chicks can be seen going for a ride around the lake on a parent’s back.Back to top


Low Concern

North American Common Loon populations have been stable overall between 1966 and 2019 according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 1.2 million and rates them 11 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. Common Loons require clear, unpolluted lakes, and can be harmed by pollution and disturbances. Regional declines have occurred at the southern edge of their range. In the Midwest, loons have disappeared from breeding sites in Illinois, Indiana, Iowa, and Ohio, and are only found in northern areas of Minnesota, Wisconsin, and Michigan. Their range has retracted in New England as well, though loon populations have rebounded there thanks to restoration efforts. Lead fishing sinkers, which loons ingest when they scoop up pebbles off the lake bottom to store in their gizzards, have been a significant cause of loon deaths from lead poisoning. Mercury, from the burning of coal, can build up in lakes through rainfall, and this has led to poor reproductive success for Common Loons in Canada, New England, and Wisconsin. Common Loons are often caught inadvertently by commercial fishing nets, both on the Great Lakes and in the ocean. Acid rain can acidify lakes, reducing fish populations that loons depend on. Human activity, particularly motorboats, can disturb loons on breeding lakes. Ocean oil spills can cause die-offs on loon wintering waters.

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Dunne, P. (2006). Pete Dunne's essential field guide companion. Houghton Mifflin Harcourt, New York, USA.

Evers, D. C., J. D. Paruk, J. W. McIntyre, and J. F. Barr (2010). Common Loon (Gavia immer), version 2.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.

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Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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