Common Loon

The Adirondacks Video
Very little conjures up imagery of the wild so vividly as the call of the loon. Yet these enigmatic birds face serious threats even in their nesting grounds in the Adirondack Park.
Common Loon Photo
As predators in northern lake ecosystems, loons are particularly susceptible to the effects of air and water pollution, which have damaging consequences as pollutants accumulate in the aquatic food chain.
Julie Larsen Maher ©WCS

The common loon is one of five loon species. This large waterbird breeds primarily in Canada and the northern United States, and as far east as Iceland and Greenland. The only loon species to breed in New York State, the common loon is an icon of Adirondack Park and the entire Northern Forest. Spending most of their lives on the water, loons are built for swimming, diving, and fishing and come ashore only to breed and nest, or when they are ill. Both males and females have striking black and white breeding plumage, as well as black bills and red eyes. Their winter plumage, by contrast, is grey and dull. After spending the summer breeding, nesting, and raising young on northern freshwater lakes, loons migrate to the ocean, where they stay through the winter.

Loons subsist entirely on a diet of fish and other aquatic animals. For this reason, they are particularly susceptible to the damaging effects of air and water pollution, which can accumulate in the aquatic food chain. The common loon is considered a Species of Special Concern in New York, Connecticut, and Massachusetts, but listed as Endangered in Vermont and Threatened in New Hampshire and Michigan. The birds’ health depends on the improvement of air and water quality throughout North America, as well as protection of their habitats.

Fast Facts

Scientific NameGavia immer
  • Loons require a long “runway” of open water to pick up speed before taking off and getting airborne.
  • Loons incubate their eggs for almost a month. Males and females take turns tending the nest.
  • Loons are known for their distinctive, wailing call, but they also hoot, tremolo, and yodel under specific circumstances.


The common loon typically lives a long life and occupies a place high on the food chain, making it a sentinel of environmental health. Loon populations are affected by air and water pollution, and face many threats related to the impacts of human activities, including recreational use of their aquatic habitat, fishing with toxic lead sinkers, and shoreline development.

Mercury, a byproduct of coal-burning power plants and trash incineration, is one of the airborne pollutants threatening loons. It is transported to the Adirondacks and other loon habitats through prevailing winds, and falls to the ground in the form of rain or snow. Along with acid rain, the mercury can then enter lakes, where it is converted into a more toxic form called methylmercury, which accumulates in the aquatic food chain. People, loons, and other top predators are most impacted by this concentration of toxins in the food supply. The neurotoxins concentrated in loon prey can affect the birds’ behavior, reproduction, and eventually, their population numbers.

WCS Responds

WCS has partnered with various organizations across the Adirondacks and the Northeast since 2001 to conserve loons and other wildlife inhabitants of freshwater through collaborative research and education. We conduct an annual common loon census with the help of local residents and visitors who volunteer their time. By getting a snapshot of the loon population each year, we are able to track changes over time, and guide management decisions and policies affecting loons. We have also partnered on a study to learn about the seasonal migratory patterns of northeastern loons, greatly increasing our knowledge about the birds’ natural history and year-round habitat use. By determining areas critical to loon populations, scientists and wildlife managers are better able to focus conservation efforts on the protection or improvement of these valuable habitats.

In cooperation with the BioDiversity Research Institute, experts from our Zoological Health Program have been performing health assessments and contributing to investigations of the effects of mercury pollution on loons’ reproductive success since 2002. A team of WCS veterinarians and veterinary technicians visit the region annually to screen loons for toxins and disease. Working with the BioDiversity Research Institute, the team pays particular attention to mercury poisoning and impacts of mercury on immune function -- health risks shown to pose significant risks to more than half of adult Adirondack loons in a 2012 study by WCS, the BioDiversity Research Institute, and the New York State Energy Research and Development Authority. In particular, high mercury levels interfere with the birds’ parenting skills: when afflicted, loons rarely incubate eggs consistently enough for chicks to hatch. As a result, their population suffers overall.

Results like these enable policymakers to better understand how environmental toxins can degrade the health of wildlife populations and their habitats. Our findings also provide natural resource managers and policymakers with a scientific basis for regulating airborne environmental pollutants on a regional scale.

In addition, WCS focuses on public participation, outreach, and education opportunities. One of our programs, the Lead Sinker Exchange, gives anglers an opportunity to exchange their lead sinkers for non-lead sinkers.

WCS Projects

Annual Adirondack Loon Census

On the third Saturday of July, WCS conducts an annual loon census with the help of local Adirondack residents and visitor volunteers. This data provides a quick glimpse of the status of the breeding loon population in and around the Adirondack Park and across New York State.

From the Newsroom

Mercury Sickens Adirondack LoonsJune 28, 2012

Loons nesting and raising their young in the New York Adirondacks are increasingly threatened by mercury contamination, which impacts reproduction and behavior. A new scientific report on Adirondack loons emphasizes the importance of reducing mercury in the atmosphere.

Savoring Bogs and Moose as the Adirondacks WarmDecember 2, 2011

WCS Ecologist Jerry Jenkins, who has spent more than four decades studying the environment of the Adirondacks, documents the impacts of climate change on the region’s wildlife, habitats, and communities.

Tenth Annual NY Loon Census a SuccessJuly 22, 2010

Volunteers who participated in the 2010 annual loon census on Saturday, July 17 surveyed more than 300 lakes and ponds in in and around the Adirondack Park and across New York State.

New Book Addresses Climate Change in the AdirondacksJuly 8, 2010

WCS ecologist Jerry Jenkins shows the global problem of climate change hitting home in the Adirondacks and how the region can fight back.

Adirondack Alarm CallMarch 7, 2008

A long-term study by the Wildlife Conservation Society, the BioDiversity Research Institute, and other organizations has found and confirmed that environmental mercury—much of which comes from human-generated emissions—is impacting the health and reproductive success of common loons in the northeastern U.S.

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