The Kelp Gull breeds on coasts and islands through much of the southern hemisphere. It is the southern equivalent of the northern hemisphere's Lesser Black-backed Gull, but averages slightly larger than that species at 65 cm in total length and 142 cm in wingspan. This is a mainly coastal gull. The nest is a shallow depression on the ground lined with vegetation and feathers. The female usually lays 2 or 3 eggs. Both parents feed the young birds.
The adult Kelp Gull has black upperparts and wings. The head, underparts, tail and the small ''mirrors'' at the wing tips are white. The bill is yellow with a red spot, and the legs are greenish-yellow. Juveniles have dull legs, a black bill, a dark band in the tail and an overall grey-brown plumage densely edged whitish, but they rapidly get a pale base to the bill and largely white head and underparts. They take three or four years to reach maturity. Kelp Gulls are omnivores like most Larus gulls, and they will scavenge as well as seeking suitable small prey. It gathers on landfills and a sharp increase in its population is therefore considered as an indicator for a degraded environment.