The red-throated loon is the smallest and lightest of the world's loon species, ranging from 21 to 27 inches in length with a 36 to 47 inch wingspan, and weighing 2.2 to 6.0 lbs. Like all loons, it is long-bodied and short-necked, with its legs set far back on its body. The sexes are similar in appearance, although males tend to be slightly larger and heavier than females. In breeding plumage, the adult has a dark grey head and neck (with narrow black and white stripes on the back of the neck), a triangular red throat patch, white underparts and a dark grey-brown mantle. It is the only loon with an all-dark back in breeding plumage. The non-breeding plumage is drabber with the chin, foreneck and much of the face white, the top of the head and back of the neck grey, and considerable white speckling on the dark mantle. Its bill is thin, straight and sharp, and the bird often holds it at an uptilted angle. Though the colour of the bill changes from black in summer to pale grey in winter, the timing of the colour change does not necessarily correspond to that of the bird's overall plumage change. The nostrils are narrow slits located near the base of the bill, and the iris is reddish.
Found in coastal waters.