Loons (Family Gaviidae) are medium to large fish-eating birds with straight dagger-like bills that capture prey by underwater pursuit. Their long bodies, with legs set far back, make locomotion on land difficult. Immature and non-breeding plumages are similar in all loon species; identification thus requires careful attention to the exact pattern of head and neck. Loons nest on the banks of lakes and ponds, and overwinter on open water.
Globally, there are five species of loons; four have been recorded in Saskatchewan. The common loon (Gavia immer) is the one most commonly seen and heard in Saskatchewan. It is known for “loon's laughter,” and is a common summer resident in lakes of northern Saskatchewan and the Aspen Parkland. It has a glossy black head and throat, a broken white neck collar, a stout, straight black bill, red-brown eyes, and a checkered black and white back. It requires disturbance-free conditions for successful nesting, and 18 m of water surface for flight take-off. The smaller red-throated loon (G. stellata) is a summer resident of the subarctic and northern boreal ecoregions in Saskatchewan, and a rare spring and fall transient in southern Saskatchewan. It has a gray head and neck, a dark and slender upturned bill, a dull red patch on the foreneck and thin black stripes on the hindneck, and a medium-gray back with small spots. The Pacific loon (G. pacifica), an uncommon summer visitant to Lake Athabasca, is a very rare spring transient and an uncommon fall transient in southern Saskatchewan. It has a dark slender bill, and pale gray nape, head and hindneck; the sides of its neck are black with white stripes; and the back is black, with rows of large white spots. The yellow-billed loon (G. adamsii) is a rare straggler species in Saskatchewan; it is very similar to the common loon, but is slightly larger and has a yellow-to-ivory bill.