The Common Loon is an iconic bird of the North Woods lakes, serving as a crucial indicator of water quality. These birds thrive in crystal-clear lakes that provide abundant small fish, their primary food source, and offer easier underwater prey visibility. Lakes with coves and islands are particularly favored for nesting due to the shelter they provide from predators. Common Loons also require sufficient open water for their distinctive takeoff, which involves flapping and running across the surface. During their wintering season along ocean coasts, they are typically found in nearshore areas, bays, and estuaries, rarely venturing more than a few miles offshore. Some populations also winter inland on large reservoirs and slow-moving rivers, using these larger bodies of water as stopovers during their migratory journeys.
Habitat Requirements
Common Loons are intrinsically linked to the health of freshwater ecosystems. Their preference for pristine, clear lakes is not merely aesthetic; it directly impacts their ability to hunt effectively. The presence of small fish populations is essential, and the clarity of the water allows loons to spot their prey beneath the surface. The landscape of their habitat also plays a significant role. Lakes offering coves and islands provide vital refuge for resting and nesting, shielding them from potential threats. Furthermore, the physical demands of their takeoffs necessitate ample open water space, free from obstructions. On the coast during winter, their habitat shifts to shallower marine environments like bays and estuaries, where they can still access suitable food sources close to shore.
Diet and Foraging Strategies
As expert anglers, Common Loons primarily subsist on a diet of fish, with perch and sunfish being common prey on their northern breeding grounds. When fish are less abundant or the water is too murky for effective hunting, they will supplement their diet with crustaceans, snails, leeches, and aquatic insect larvae. Their underwater foraging is a remarkable display of agility and speed. Loons propel themselves through the water like torpedoes, using powerful thrusts of their feet, which are positioned towards the rear of their body. They possess an astonishing ability to change direction instantaneously, executing sharp turns by using one foot as a pivot and brake while kicking with the other. This maneuverability rivals that of Olympic swimmers and allows them to effectively pursue agile prey. In their wintering grounds, their diet includes small fish such as Atlantic croaker, and they have been observed cooperating in groups to hunt schools of silversides.
Nesting Behavior and Reproduction
The nesting process of the Common Loon is a carefully orchestrated affair, beginning with the male selecting a suitable nest site. Loons seek out quiet, secluded locations along lake shores, often in sheltered bays or on the leeward side of islands. Their limited terrestrial mobility influences nest placement; they build close to the water’s edge, frequently with a steep bank that allows for an easy underwater approach to the nest. In areas with extensive shoreline development, artificial nesting platforms have been provided as an alternative habitat. It is common for a pair to return to and refurbish the same nest site year after year.
Both the male and female collaborate in constructing the nest, typically over a week in May or early June. They create a mound using dead plant materials like sedges and marsh grasses gathered from the lake’s edge. One of the loons then settles into the mound, shaping the interior to fit its body. The completed nest resembles a clump of dead grasses situated at the water’s margin and measures approximately 22 inches in width.
The reproductive cycle involves a clutch size of 1-2 eggs, with usually only one brood per year. The eggs are brown with dark splotches and measure about 3.5 inches in length and 2.2 inches in width. Incubation lasts for 26-29 days. Upon hatching, the chicks are covered in down, appearing sooty black with a white belly. Remarkably, they are capable of swimming and riding on their parents’ backs within hours of hatching.
Behavioral Ecology
Common Loons dedicate a significant portion of their day to foraging in shallow waters. They are often observed swimming slowly, immersing their heads to scan for fish before executing a sudden, almost ripple-less dive to capture their prey. Their hunting activities are primarily diurnal, taking advantage of daylight for optimal visibility. An intriguing behavior observed is the loon’s habit of sticking one foot out of the water and waggling it, a behavior believed to aid in thermoregulation, particularly on warm, sunny days.
Territorial displays involve the loon rearing its body upright and flapping its wings vigorously. This display might be witnessed by canoeists who venture too close, often accompanied by a defensive “tremolo” call as the loon retreats. Loons also use the tremolo call during flight between lakes or when flying in circles above a lake, with their necks extended and feet trailing. They are known for their vocalizations, especially nocturnal choruses where their wails, yodels, and tremolos echo across the North Woods lakes.
In the spring, mates return to their breeding lakes separately. Common Loons are monogamous, with pair bonds often lasting around five years. If a mate fails to return one year, the surviving loon will typically find a new partner. Territory establishment is often marked by the male’s yodeling. Courtship involves synchronized dives and swimming in circles. Successful nesting results in chicks that are often seen riding on a parent’s back as they explore the lake.
Conservation Status and Threats
Overall, North American Common Loon populations have remained stable between 1966 and 2019, according to the North American Breeding Bird Survey. Global breeding population estimates suggest around 1.2 million individuals, and the species is considered to be of relatively low conservation concern. However, regional declines have been noted at the southern edges of their range, with extirpations occurring in states like Illinois, Indiana, Iowa, and Ohio. Their presence has also retracted in parts of New England, though restoration efforts have aided in population rebounds in some areas.
Several threats jeopardize Common Loon populations. The ingestion of lead fishing sinkers, mistaken for pebbles to aid digestion, leads to fatal lead poisoning. Mercury, a byproduct of coal burning, can accumulate in lakes through rainfall, impacting reproductive success. Loons can also become entangled in commercial fishing nets, both in the Great Lakes and offshore. Acidification of lakes due to acid rain reduces fish populations, diminishing their food source. Human activities, such as disturbance from motorboats on breeding lakes, can disrupt nesting and foraging. Additionally, ocean oil spills pose a significant threat to their wintering grounds.
References
- 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.
- Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.
- Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.
- Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.
- Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.
