Observations and dispersal of black-billed gulls (tarāpuka, Chroicocephalus bulleri) banded at North Canterbury, New Zealand, 1958–1974 and 1983

A total of 15,694 black-billed gulls (tarāpuka, Chroicocephalus bulleri) chicks were banded at six braided gravel-bed rivers in North Canterbury, New Zealand, from 1958 to 1983, and at least 1,754 later sightings of dead or alive birds were reported to the Banding Office. The main banding sites were the Ashley River and its major tributary, the Ōkūkū River; other banding was carried out on the Kowhai River near Kaikoura, Conway River, Waiau River, Waipara River, and Waimakariri River. Colonies typically shifted location between years, as flooding and weed growth affected the habitat and suitability for nesting. Up to 6 colonies were found on the Ashley River system in a season. Average size of all colonies was about 230 nests, with the largest reaching about 800 nests. Some birds were found at rivers apart from their natal rivers. Birds bred when as young as 2-years-old. The furthest sighting was at Firth of Thames, 736 km NE of the banding site; the southernmost was at Waipahi, Otago, 412 km SW of the banding site; and the oldest recovery was 22.1 years after banding. Band loss likely affected recovery rates, as the oldest bird found with an aluminium band was only 10.9 years-old.