Notes From the Field: Common Loon banding and conservation
“Notes from the Field” are contributed articles that highlight current banding projects and the continued importance of bird banding mor than a hundred years after the establishment of the Bird Banding Lab. This article highlights the value of Common Loons (Gavia immer) as environmental indicators and how banding has aided in the conservation of the species across the United States and Canada.
“Notes From the Field” news articles highlight the continued importance of bird banding. This article was contributed by Biodiversity Research Institute (BRI) which began researching Common Loons back in 1989. BRI has banded more Common Loons than any other North American Bird Banding Program permittee, with 6,884 Common Loons banded to date in 21 US states, 8 Canadian provinces, and in Iceland.
Banding allows scientists to investigate bird behavior, migration, lifespans, populations, diseases and levels of environmental contaminants. Information gathered through the North American Bird Banding Program helps inform management and conservation decisions for game and non-game species, such as protecting or restoring habitat, setting hunting regulations and determining plans for human-led development. The North American Bird Banding Program depends on a network of over 10,000 permitted bird banders working in the United States, Canada and Trust Territories. Each year these banders help us add up to 1.2 million new banding records to our century-long dataset.
Why is your study species so interesting?
The Common Loon is one of five loon species that exist worldwide and is the only loon that breeds in the relatively low latitudes of the contiguous United States. The closely related, Yellow-billed Loon (Gavia adamsii) is a strictly tundra and coastal plain breeding species and is the rarest loon species. Pacific (G. pacifica) and Arctic loons (G. arctica) are both smaller than the Common Loon and, while the Pacific Loon is mostly restricted to northern North America, the Arctic Loon primarily breeds in Europe and Asia. Lastly, the Red-throated Loon (G. stellata) has the widest range of all loon species and breeds across the higher latitudes of the Northern Hemisphere.
The Common Loon is often associated with the North Woods— and prefers habitats of clear, deep lakes surrounded by tall spruce and pines. However, these loons live widely and in a variety of habitats, including shallow and managed pools, turbid reservoirs, beaver ponds, sphagnum bog lakes, and relatively high elevation lakes.
In winter, the loon’s habitat varies just as widely. Loons overwinter along the Atlantic (as far south as Texas) and Pacific (into Mexico), and on freshwater lakes and rivers that remain ice-free. On the southern fringes of the winter range, loons occupy coastal shorelines near the arid, cactus-lined shores of Mexico, or in bays ringed with live oak and Spanish moss.
How/why was this project started? What question(s) are you trying to answer through your research?
In 1989, BRI founder David Evers, then a graduate student, discovered a reliable and replicable way to capture loons. That singular event opened opportunities for wildlife biologists to conduct demographic, behavioral, and contaminant studies on the iconic bird Sigurd Olsen described as a “symbol of wildness.”
Loon capture not only provided a way to assess contaminant levels in our lakes and waterways, but also later served to determine how mercury pollution affects behavior and reproduction. Common Loons are considered reliable indicators of mercury pollution in lakes. As large, long-lived birds that feed nearly exclusively on fish and tend to nest on nutrient-poor lakes, loons have been identified as one of the most important indicators of the health of the aquatic environments they occupy.
Loons are smart, elusive, and can dive to depths up to 200 feet. Over the course of nearly three decades of loon research, BRI wildlife biologists perfected nighttime capture techniques.
To catch loons, our biologists launch the boat out on the lake before dark to locate pairs with chicks. Once the sun sets and darkness falls, we slowly approach the pair, using a spotlight to locate them on the water. Loons are fiercely protective of their young, especially from other loons that might try to kill their young and cause pairs to give up a breeding territory and will try to drive off potential competitors. We use loon calls (yodels, wails, chick peeps, and hoots) to attract the adults, who swim towards the sounds they perceive as a competitor. The spotlight both hides the boat from their view and allows us to see and net the bird and bring it into the boat.
Once in hand, loons are impressive. Their plumage is as striking up close as from afar, and they are incredibly muscular and strong. To protect the bird and ourselves, we gently wrap a towel around the head (ensuring the bill is not restrained) and tuck the now wrapped head under the holder’s arm. We band loons with a custom-fit USGS band, which we form on-site to the dimensions of each individual bird’s leg. Loons can vary widely by size, with some males weighing over 15 pounds. Each bird is fitted with a unique combination of four bands including the aluminum USGS band and three colored bands, allowing us to resight and identify the bird for many years. Just this past summer, we recaptured a female loon that was first banded as a breeding adult in 1996!
While we have the loons in hand, we also take measurements to better understand variation in body size among individuals and populations. We sample blood from the loons to monitor contaminants such as mercury and PFAS (per- and polyfluorinated substances, a suite of emerging contaminants that seem pervasive in wildlife populations). Feathers are also used for contaminants monitoring, and through collaborators, we can test the birds for avian malaria, health biomarkers, and other physiological metrics that allow us to assess how contaminants and disease are associated with bird health. At many of our field sites, we have been able to recapture individuals multiple times to see how contaminant exposure and body measurements change over time.
How has bird banding/marking changed during this project?
Nighttime methods of loon capture proved inadequate in the Arctic (and in areas where loons are unaccustomed to boats and lights). In response, field crews developed a site-specific methodology that allowed the capture of loons during the long daylight hours in that region. As loons will defend their breeding territory from other loons, we use decoys and calls to capture loons in the daylight, either with floating or submerged nets that we can raise out of the water to keep the loon from escaping. These same approaches have been modified still further to capture loons that get frozen in the ice in late fall and winter.
Why do you think projects like yours are so important?
Until the late 19th century, breeding populations of loons could be found in lake habitats throughout Canada, south to Pennsylvania, Indiana, Illinois, Iowa, and west to California. In the Northeast, breeding loons could be found throughout New York and all New England states except Rhode Island.
However, human activities such as sport hunting practices and shoreline development caused loon populations to suffer serious declines. Over the course of a century, their southern range was greatly reduced. In some areas, including Massachusetts, loons disappeared completely by the late 1800s.
In 2013, BRI began one of the largest loon studies ever conducted. The initial five-year scientific initiative aimed to strengthen and restore Common Loon populations within their existing and former range. This project was the first translocation study to be conducted for a loon species. During this project, BRI staff developed the methods for captive rearing loon chicks in aquatic pens.
Translocation—moving chicks from natal lakes to a new lake location and confirming that they fledged from that lake to migrate to wintering grounds.
What have you found so far? Any surprises? Major accomplishments?
A male loon chick that was translocated in 2015 from the Adirondack Park Region of New York to the Assawompsett Pond Complex in southeastern Massachusetts returned in 2018 to the region from which it fledged. In the 2020 breeding season, this now adult formed a territorial pair, nested, and successfully hatched a chick in Fall River, Massachusetts. The identification of this loon (through colored bands) marks the first confirmed nesting pair in southern Massachusetts in more than a century.
Settlement funding from the 2003 Bouchard Barge 120 oil spill was awarded to BRI to restore Common Loons to their former breeding range in Massachusetts and to strengthen existing breeding populations within other parts of the state.
That project, which concluded with the 2024 breeding season, resulted in the resighting of 19 adult loons from a total of 36 (53%) translocated to southeastern Massachusetts during 2015-2017 and 2020. Of those resighted, 12 first returned to the lakes in Massachusetts to which they were translocated and captive-reared, and from which they fledged. We will continue to monitor return rates of translocated chicks since 2020 as they become sexually mature and recruit into the breeding population.
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
All banding, marking, and sampling is being conducted under a federally authorized Bird Banding Permit issued by the USGS BBL.
The “Notes From the Field” series highlights current banding projects and the continued importance of bird banding and the Bird Banding Lab. Want to see your project featured in a future “Notes From the Field” article? Email Kyra Harvey kharvey@usgs.gov for submission details.
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