Common Loon
| Scientific Name | Dolichovespula maculata |
| Survival Strategy | Medium-distance migrant |
| Arrival in Upper Midwest | Mid to late April (at ice-out) |
| Departure | Late August (adults) November (hatch-year) |
| Destination | Gulf of Mexico, Atlantic Coast |
| Conservation status | Least Concern |
Winter
Loons spend the winter off the Atlantic Coast and the Gulf of Mexico. They go through a molt in February before returning to the Upper Midwest, shedding the dull grey feathers that got them through the winter. As they are transitioning into the iconic black and white plumage, they are flightless.
Spring
Returning loons arrive at the breeding grounds as the last ice leaves the northern lakes. In late April and early May, loons establish and defend their territories. Nest building takes place in May, and the female lays one or two eggs in late May.
Summer
The eggs hatch by mid-to-late June and intensive chick-rearing lasts throughout July. In early August, adult loons leave their chicks and form pre-migratory social groups with other loons. A mid-August molt produces fresh feathers and a dull grey plumage that makes the adults look like their offspring.
Fall
Adults begin their migration to their subtropical wintering grounds in late August and early September. Juveniles leave in early November and will remain at sea for three years.
Behavior
Habitat Selection
Male loons select the nest site. An ideal location is on a clear-water lake, at least 15 acres in size, with deeply indented shorelines and a good supply of small fish. Quiet spots sheltered from the wind are preferred. Because loons are awkward on land, they must build their nests close to the water.
Territoriality
Loons often acquire new territory by battling the current occupants of the lake. Territorial battles involving males or females often result in one of the combatants dead. Loons may also replace a deceased mate or search out an unclaimed location and start a nest from scratch.
Physiology
Staying warm
Common loons employ a “dress in layers” strategy for cold weather familiar to many outdoor enthusiasts. Their contour feathers create a windproof and waterproof outer layer, while their down feathers serve as an insulating base layer. Unlike humans, birds do not sweat, which would reduce the insulating value of the down feathers.
These diving birds keep their contour feathers dry by preening oil from the uropygial gland near the base of their tail, ensuring the down layer next to the skin stays dry. Down feathers do not insulate well when wet. By fluffing their contour feathers (piloerection), the bird traps air that increases the insulation value of the down layer and reduces the number of calories needed to survive the cold.
Swimmer’s Body
Loons are powerful swimmers and can dive to almost 200 feet and stay underwater for more than five minutes. With their feet positioned at the rear of the body, loons are a model of hydrodynamic perfection. On land, physics is less kind. They cannot walk and will awkwardly scoot the few feet needed to reach their nest on their chest. Nesting is the only time a loon is on land.
Loons control their buoyancy by adjusting the volume of air they carry inside and outside of their body. They can expel air from their air sacs (which pump air into and out of the lungs). They also use piloerection to compress their feathers to reduce the air in their down feathers.
Loons have other adaptations for life as aquatic hunters. Unlike most birds, loons have solid bones, making them less buoyant. They also have a transparent inner eyelid called a nictitating membrane that protects their eyes during dives and flights. A loon’s nervous system will slow down its heart while diving to reduce oxygen demand. Like other marine birds, loons have glands above their eyes that remove excess salt, which they expel through their nostrils. Any exposure to spilled oil can interfere with the functioning of this gland.
Diet
The common loon’s diet consists mainly of small fish less than 25cm (10in) long, crayfish, and insect larvae (chicks). They will eat about two pounds of fish per day, which they swallow headfirst to prevent the fin ribs from getting caught in the esophagus. They eat small stones from the lake bottom to use in their gizzard to grind their food. If they should swallow a discarded lead sinker by mistake, it is almost always fatal.
Lifespan and Mortality
Loons that make it to adulthood will likely live 15 – 25 years. Almost 50% of all loon chicks will not survive until the age of three. Loons over the age of three have a yearly survivorship rate of about 92%
Predators
Loon eggs are eaten by crows, ravens, raccoons, skunks, and bald eagles. Loon chicks are eaten by bald eagles, snapping turtles, and large fish such as muskie and bass. Predators of adult loons include bald eagles and sharks (in wintering grounds).
Human Impact
Lead poisoning due to the ingestion of lead fishing tackle is a leading cause of loon death. Swallowing lead fishing tackle is almost always fatal. Curious paddlers can disrupt incubation and cause the loon to abandon the nest.
Climate Vulnerability
Climate modeling suggests that the winter and summer range of the common loon will shift north. By the end of the century, the upper Midwest will likely no longer be the summer home for loons.
Never stop learning
Paleontology: Fossil evidence of loon-like birds dates back more than 7 million years
First Nations: The Ojibwe word for loon is “maang.”
Currency: The $1 Canadian coin is known as a “loonie” because it has an image of a loon on one side.
References
| Paruk, J. D., D. C. Evers, J. W. McIntyre, J. F. Barr, J. Mager, and W. H. Piper (2021). Common Loon (Gavia immer), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.comloo.02 |
| Common Loon Migration Study https://www.umesc.usgs.gov/terrestrial/migratory_birds/loons/main.html |
| Common Loon: Audubon Field Guide https://www.audubon.org/field-guide/bird/common-loon |
| The Loon Project https://loonproject.org/ |
| Kevin P. Kenow, David Adams, Nina Schoch, David C. Evers, William Hanson, Dave Yates, Lucas Savoy, Timothy J. Fox, Andrew Major, Robert Kratt, and John Ozard “Migration Patterns and Wintering Range of Common Loons Breeding in the Northeastern United States,” Waterbirds 32(2), 234-247, (1 June 2009). https://doi.org/10.1675/063.032.0204 |
| Ask the Scientist – National Loon Center Foundation https://www.nationallooncenter.org/ask-the-scientist/ |
| Video: Loons of Mount Desert Island, Maine. Cornell Lab of Ornithology https://youtu.be/1X5TwF1LSxY |
| Video: Unraveling Mysteries of the Common Loon https://youtu.be/6YG4bsOfISY |
| Ojibwe People’s Dictionary: Loon https://ojibwe.lib.umn.edu/main-entry/maang-na |