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March 2023

The ‘Great Northern Diver’ – Common Loon Sightings Becoming Increasingly Rare in the Great Lakes Region

by Scott Brown
MWA e-Newsletter Editor

Prompting the return of a flood of fond memories of northern pike and walleye fishing with my son and grandson while on fly-in fishing trips to northern Ontario’s Shabuskwia Lake, the other worldly sound of a loon’s call has always held special meaning for this ageing baby boomer.  Although I have not visited this gorgeous wilderness lake in many years, my son and wildlife biologist grandson tell me that loon sightings even in the far north have become increasingly rare.

Although there are five species of loon in North America – all member of the Family Gaviidae, including Red-throated Loon, Pacific Loon, Yellow-billed Loon, and Arctic Loon, the most abundant is the Common Loon (scientific name: Gavia immer). The International Union for the Conservation of Nature reports that the majority of the approximately 640,000 common loons that remain on earth are found in Canada.

Though they are awkward on land due to the fact their legs are placed far back on their bodies, common loons have evolved as water birds that venture onto shore only to mate and incubate eggs, and learn how to dive long before they learn how to fly. Though the name loon derives from their goofy, awkward walk, they are often referred to as ‘great northern divers’. Capable of staying submerged for up to five minutes as they forage for fish and aquatic insects, loons are particularly well adept at hunting underwater due to their solid bones that make them less buoyant, their capacity to rapidly expel air from their lungs, and their ability to flatten their feathers in order to expel air from their plumage. The capacity to stay submerged for long periods is also enabled by their extraordinary physiological capacity to slow their heart rate while diving in order to conserve oxygen. The red eyes of loons have also evolved to allow them to detect fish and other prey in the low light conditions that are often present in water depths of up to fifteen feet. Empowered by their capacity to rapidly descend and to swim at an extraordinary fast pace while underwater, loons are considered highly effective hunters that are capable of consuming a large quantity of small fish in relatively short order. Biologists familiar with the unique bird species have estimated that a single set of loon parents and their two chicks are capable of eating a half ton of fish in a single fifteen-week season. Due to their reliance upon diving to depths of up to fifteen feet to forage for food, loons prefer healthy inland lakes hosting relatively clear water and healthy fisheries. Loons are known to shy away from inland lakes suffering from poor water clarity. Frequent loon sightings in a particular region are considered a reliable indicator of the presence of large, healthy inland lakes hosting abundant fish populations, relatively clear waters, and the existence of undisturbed natural shorelines.

Graced with relatively small wings in comparison to their size and weight, loons are attracted to large lakes that provide them with an opportunity to takeoff into the wind and skitter across the water’s surface for a long distance before creating enough aerodynamic lift to eventually become airborne. Once airborne, however, common loons are capable of flying at speeds of up to 70 miles per hour. It is interesting to note that their need for long, water-based take off ‘runways’ has caused migrating common loons to become stranded as they sometimes mistake wet highways and parking lots as rivers and lakes.

Due to their relatively large bodies, small wings, and the fact that their fast flight requires a lot of energy that must be replenished along the way, common loons are considered a medium-distance migrants. The common loons of the northern United States and Canada migrate from lakes to the coastal oceanic waters of the Pacific or Atlantic. The loons of western Canada and Alaska migrate to the Pacific Coast ranging from Alaska’s Aleutian Islands to Mexico’s Baja Peninsula. Great Lakes region common loons migrate to the Gulf of Mexico or Florida coasts. Common loons that inhabit the lakes of eastern Canada migrate to the North Atlantic Coast.

Sharp declines in the abundance of all five loon species in North America have thus far been primarily attributed to the loss of critical habitat caused by steadily increasing rates of near shore residential development that has been occurring on thousands of larger northern temperate inland lakes located in the United States and Canada. Intensive lakefront development facilitated loss of optimal loon habitat and a commensurate loss of preferred nesting and rearing habitat is one of the primary reasons that loon populations have experienced a steady decline over the course of the past fifty years.  Ecologists familiar with the decline of loon populations in North America also indicate that multiple stressors including the not yet well understood influences of climate change, diminished fish populations, acidification of inland lakes, and the loss of eggs and chicks to an increasing number of scavenging predators have also contributed to the decline of loons. It is important to point out that common loon populations in the Laurentian Great Lakes region have also experienced decline due to the onset of increasingly frequent outbreaks of  Type-E botulism that has caused massive annual die-offs of common loons, and other fish-eating birds in the past twenty five years.