The red-throated loon or red-throated diver (Gavia stellata) is a migratory aquatic bird found in the northern hemisphere.
Ranging from 55–67 centimetres (22–26 in) in length, the red-throated loon is the smallest and lightest of the world’s loons. In winter, it is a nondescript bird, greyish above fading to white below. During the breeding season, it acquires the distinctive reddish throat patch which is the basis for its common name. Fish form the bulk of its diet, though amphibians, invertebrates and plant material are sometimes eaten as well. A monogamous species, the red-throated loon forms long-term pair bonds. Both members of the pair help to build the nest, incubate the eggs (generally two per clutch) and feed the hatched young.
The red-throated loon has a large global population and a significant global range, though some populations are declining. Oil spills, habitat degradation, pollution and fishing nets are among the major threats this species faces.