Red-billed gulls breed in about 80 colonies on New Zealand's North and South Islands (mostly on the east coast of both islands), on offshore islands and in the Chatham Islands. Many birds fly several hundred kilometres between their breeding colony, which they return to each year, and sites where they spend the winter. Most birds stay within 400km of their breeding colony. There are also several inland breeding colonies at Sulphur Point at
Lake Rotorua, which increased in size between the 1990s and 2010. Māori history recalls that in 1823,
Te Arawa people living on
Mokoia Island in
Lake Rotorua were attacked by the
Ngāpuhi tribe. The Te Arawa people were warned of the attack when a flock of red- and black-billed gulls disturbed by the attackers flew up, squawking an alert. After the battle, Te Arawa honoured the gulls by declaring them
tapu or sacred. The national population of red-billed gulls increased between the 1930s and 1970. A 1965 analysis estimated that at that time there was a national breeding population of 40,000 pairs of birds, At Mokohinau, an expedition in November 1933 observed thousands of nesting red-billed gulls. The colonies at Three Kings Islands and Mokohinau have declined by more than 80 per cent since the 1990s, for reasons yet unknown: by 2016, there were only 1763 breeding pairs at the Three Kings Islands, and 58 at Mokohinau. The 2014–2016 study found that the largest mainland colonies were at Kaikōura (3210),
Taiaroa Head (2145),
Rotorua (2277) and
Marsden Point (1190). The only large colonies on off-shore islands were at the Three Kings Islands (1763 pairs) and
Stephens Island (1250 pairs). The increase in red-billed gulls at Taiaroa Head is due to predator control at the
albatross colony there. ==Behaviour==