On Dec 7, 2012, RosinaBloom from Waihi New Zealand (Zone 1) wrote:
The Red-billed Gull is one of the commonest gulls on the New Zealand coast. It rarely lives inland, and its breeding colonies are mainly found on the eastern coasts of the North and South Islands. Dense colonies nest in the open on barren stacks and islands, whereas elsewhere the nests are concealed and located in small groups or singly. The main food during breeding season is planktonic crustaceans, earthworms, kelp-fly larvae, and fish larvae. They feed inshore on foraging trips that last about 2 hours. Outside the breeding season the diet is more varied. Some birds continue to feed at sea, some forage along the shore for marine invertebrates, and others eat refuse. They harass other birds, and attempt to force white-fronted terns, gannets, oystercatchers, shags and even other Red-billed gulls to drop food they are carrying. They force young shags to disgorge food their parents have just fed them. Some rob nests of eggs. The breeding season extends from July to January . Many gulls breed at the natal colony, and once they have bred at one site they often return, usually with the same partner. From late July onwards the birds defend the nest site, and spend more and more time there until 12 days before laying. The gulls display aggressively but rarely fight. The first sites claimed are the central or elevated parts of the colony. They are capable of breeding at 2 years. Nest building - which is often constructed of seaweed, sticks and grasses - begins about 2 or 3 weeks before egg laying, and though both parents share nest construction, most of the material is collected by the male. The normal clutch is 2 eggs, which both parents incubate. The eggs hatch 24 to 27 days after being laid, the chicks remain in the vicinity of the nest, and are seldom left unattended. Any that wander onto an adjacent territory are attacked or even killed by other adults. The sexes are alike, although the male is larger with a stouter and slightly longer bill. The bill, eyelids and feet are scarlet in the breeding season,and duller during the rest of the year. Interbreeding between Red-billed and black-billed gulls has been recorded at Lake Rotorua. The hybrids have proved to be fertile, and have bred with Red-billed gulls. The birds begin to leave the colony in mid January. Banded gulls from Kaikoura sometimes wander as far away as Invercargill and Auckland, but most remain within 380 km of their colony. Juveniles seem to disperse slightly further than the adults.