The Common Loon is an iconic bird of the North Woods, serving as a crucial indicator of water quality. These magnificent birds thrive in crystal-clear lakes, essential for their ability to spot prey underwater and for their own survival. Their habitat requirements extend to lakes with ample small fish populations, coves, and islands that offer protection during rest and nesting periods. A significant surface area is also necessary for their unique take-off, a running-and-flapping process across the water. During the winter months, Common Loons migrate to ocean coasts, favoring areas near the shore, including bays and estuaries, and are seldom found far offshore. Some loons also overwinter inland on large reservoirs and slow-moving rivers, utilizing these bodies of water as stopovers during their migratory journeys.
Habitat Requirements
Common Loons are intrinsically linked to the health of freshwater ecosystems. They exhibit a strong preference for pristine lakes characterized by exceptionally clear water. This clarity is paramount, as it directly impacts their foraging success by allowing them to easily locate their primary food source: small fish. Beyond water clarity, loons seek lakes that offer a diverse topography, including coves and islands. These features provide essential shelter and concealment from potential predators, offering a safe haven for resting and nesting. Furthermore, the ability to take flight is critical for loons, and this requires lakes with sufficient open water to accommodate their distinctive takeoff, which involves running and flapping across the surface. On their wintering grounds along the coast, Common Loons adapt to a marine environment, typically staying relatively close to the shore in bays and estuaries. While they primarily inhabit coastal waters, they are occasionally observed on large inland reservoirs and slow-moving rivers. Migratory loons navigating across North America rely on a network of large lakes and rivers to facilitate their journeys.
Diet and Foraging
As expert anglers, Common Loons primarily subsist on a diet of fish, with perch and sunfish being particularly favored in their northern lake habitats. When fish become scarce or water conditions are unfavorable for sight-fishing, their diet diversifies to include crustaceans, snails, leeches, and even aquatic insect larvae. The underwater hunting techniques of loons are a remarkable display of avian adaptation. They move through the water with incredible speed and agility, propelled by powerful thrusts of their feet, which are positioned far back on their bodies. Their ability to maneuver is equally impressive; when their prey changes direction, loons can execute rapid, 180-degree turns. This is achieved by extending one foot laterally to act as a pivot brake while simultaneously kicking with the opposite foot. This instantaneous change in direction would rival that of any Olympic swimmer. In their wintering grounds, loons adapt their diet to the available prey, often consuming small fish like Atlantic croaker. They have also been observed to cooperatively hunt, with groups of loons banding together to chase schools of Gulf silversides.
Nesting Behavior
Nest Site Selection and Description
The selection of a nesting site is primarily undertaken by the male Common Loon. Loons exhibit a preference for secluded, sheltered locations along lake shores, often choosing spots protected within coves or bays. Because loons are not adept walkers on land, their nests are strategically built very close to the water’s edge, frequently with a steep drop-off. This proximity allows them to easily enter and exit the nest from the water. In areas with significant shoreline development, artificial nesting platforms have been introduced and are frequently utilized by loons as alternative nesting sites. It is common for nesting pairs to return to and refurbish the same nest year after year, rather than constructing a new one.
Both the male and female collaborate in building the nest, a process that typically takes about a week in May or early June. They construct a mound using dead plant materials, such as sedges and marsh grasses found along the lake’s edge. One of the loons then settles onto the mound, shaping the interior to conform to its body. The completed nest is approximately 22 inches wide and, from a distance, resembles a clump of dead grasses situated at the water’s margin.
Nesting Facts
- Clutch Size: 1-2 eggs
- Number of Broods: 1 brood per year
- Egg Length: 3.5-3.5 inches (8.8-9 cm)
- Egg Width: 2.2-2.2 inches (5.5-5.7 cm)
- Incubation Period: 26-29 days
- Nestling Period: Approximately 2 days before chicks are ready to leave the nest.
- Egg Description: The eggs are brown and marked with dark splotches.
- Condition at Hatching: Chicks are covered in down, appearing sooty black with a white belly. They are capable swimmers and riders on their parents’ backs within hours of hatching.
Behavioral Patterns
Common Loons dedicate a significant portion of their day to foraging in shallow waters. They are often observed swimming slowly, with their heads partially submerged, scanning for fish. Once prey is spotted, they execute a sudden, precise dive, often leaving minimal ripple on the water’s surface. Their foraging activities are exclusively diurnal, as they rely on daylight for effective prey detection.
Interestingly, loons sometimes display a peculiar behavior of extending one foot out of the water and wiggling it. Scientists hypothesize that this may be a thermoregulation mechanism, as the behavior is observed more frequently on sunny, midsummer days, suggesting it helps them cool down.
Social interactions and territorial displays are also prominent. Loons engage in a territorial display where they lift their bodies upright and vigorously flap their wings. This display can be triggered when canoeists approach too closely. It may be accompanied by a defensive “tremolo” call as the loon retreats. The tremolo call is also vocalized when loons fly between lakes or circle above a lake, with their necks extended and feet trailing.
Nocturnal vocalizations are another striking characteristic of Common Loons. After sunset, many North Woods lakes are filled with the echoing sounds of their wails, yodels, and tremolos, which have been poetically described as “the laugh of the deeply insane.”
Common Loons are monogamous, with pair bonds typically lasting for approximately five years. If one mate fails to return in a given year, the surviving loon will promptly seek a new partner. The male establishes his territory through yodeling. Courtship rituals involve swimming in circles and synchronized dives. Successful nesting often results in the visible sight of loon chicks riding on a parent’s back as they explore the lake. The phenomenon of loons congregating in groups to hunt schools of small fish, such as Gulf silversides, highlights their adaptability and social dynamics in foraging.
Conservation Status and Threats
The overall North American population of Common Loons has remained stable between 1966 and 2019, as indicated by the North American Breeding Bird Survey. Partners in Flight estimates the global breeding population at 1.2 million and classifies them with a Continental Concern Score of 11 out of 20, suggesting a species of relatively low conservation concern.
Despite this overall stability, Common Loons face several threats that can impact regional populations and individual birds. Their reliance on clear, unpolluted lakes makes them vulnerable to environmental degradation. Pollution and disturbances can significantly harm loon populations. Notably, regional declines have been observed at the southern edges of their breeding range. In the Midwest, Common Loons have disappeared from breeding sites in Illinois, Indiana, Iowa, and Ohio, and are now primarily found in the northern regions of Minnesota, Wisconsin, and Michigan. Their range has also contracted in New England, although dedicated restoration efforts have contributed to population rebounds in these areas.
A significant cause of mortality for Common Loons is lead poisoning, resulting from the ingestion of lead fishing sinkers. Loons accidentally swallow these sinkers when picking up pebbles from the lake bottom to aid digestion in their gizzards. Mercury contamination, originating from the burning of coal, can accumulate in lakes through rainfall. This mercury has been linked to poor reproductive success in Common Loons in regions such as Canada, New England, and Wisconsin.
Furthermore, Common Loons are susceptible to entanglement in commercial fishing nets, both in the Great Lakes and in ocean waters. Acid rain poses another threat by acidifying lakes, which in turn reduces the fish populations essential for the loons’ diet. Human activities, particularly the disturbance caused by motorboats on breeding lakes, can negatively impact nesting success. Finally, ocean oil spills can lead to significant die-offs in the loons’ wintering waters.
