Marbled Murrelet are a chubby, “robin-sized” seabird (actually a small auk), with short neck and tail. The characteristic profile while swimming is for the tail and black bill to be tipped upwards. During the breeding season (summer), plumage on the back is dark brown with marbled light brown sides and stomach (camouflaging adults on the nest). Winter plumage becomes more distinct with the back darkening to black, and sides, belly, and wing patches becoming white along with a broken white collar. These colouration patterns also help to camouflage the marbled murrelet from predators on the open ocean as well as during underwater foraging. Juveniles have a similar size and body shape as adults but plumage has more extensive marbling that lasts over the winter until sexually mature.