The Slaty-backed Gull, Larus schistisagus, is a robust seabird with a commanding presence. It is recognized by its large size, with a length ranging from 55 to 68.5 cm, a wingspan stretching between 132 and 160 cm, and a weight from 1.05 to 1.7 kg. This gull boasts a white head, belly, and tail, contrasted by a dark slaty-gray back and wings, edged with a broad white trailing edge.
Adult Slaty-backed Gulls have yellow eyes set in purple to deep pink orbital skin, and their legs are a soft pink. Their stout build gives them a "pot-bellied" appearance, and their legs are relatively short compared to similar species. The bill is a striking yellow with an orange-red subterminal spot. One of the most distinctive features is the "string of pearls" wing pattern on the mid-primaries, a series of white crescents that connect to the white trailing edge of the secondaries. Immature birds display a brown plumage, lighter than that of the Great Black-backed Gull, and can be difficult to distinguish from immature Herring Gulls in the field.
The Slaty-backed Gull is native to the Pacific coast of northeastern Asia, where it breeds.
Outside the breeding season, this gull becomes a wide traveler, with individuals having been recorded across North America, from New England to Texas, and even as far afield as Finland.
This species is known for its extensive travels during the nonbreeding seasons, showcasing its adaptability and exploratory nature.
The Slaty-backed Gull is similar in appearance to the Western Gull and the Glaucous-winged Gull. However, it can be distinguished by its unique wing pattern and the darker shade of its wings and back.
The Slaty-backed Gull is currently listed as Least Concern on the IUCN Red List, indicating that it is not at immediate risk of population decline.