Black-billed gulls

Status: Nationally Critical

Over a two-month period in 2006, one cat and a ferret killed hundreds of black-billed gull chicks on the Aparima River in Southland.

Black-billed gulls and chicks, the most threatened gull in the world, on the Conway River
Black-billed gulls and chicks, the most threatened gull in the world, on the Conway River

While they still number in the thousands, their total numbers are rapidly declining. The majority nest in colonies in the South Island, primarily Southland, from August-February. Colonies often change from year to year on braided rivers through to single-channel rivers and streams with gravel beds.

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Occasionally birds resort to nesting on adjacent farmland after major flood events or when they can find no suitable breeding habits on riverbeds (also see short news video).

In the North Island, the most well-known colony is on the shores of Lake Rotorua. Elsewhere in the North Island, black-billed gulls nest on coastal shell banks and sand spits. Recently, the breeding range has expanded in the North Island as far north as the Kaipara Harbour.

After the breeding season, most South Island birds migrate to the coast, though movement patterns are poorly known (distribution map – somewhat dated but still useful).

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Description

Endemic (unique) to New Zealand, the black-billed gull (Larus bulleri) also known as Buller’s gull, tarāpuka, tarapuka (Māori), seagull, black-billed gull, and black billed gull, is a medium-sized gull measuring 35-38cm and weighing 230grams. Unlike other common gulls, black-billed gulls are not normally scavengers, and so they are less likely to be found in towns and cities.

The wings and back are pale grey, with white-tipped black margins to the main flight feathers. The eye-ring is black and the iris is white. The legs are black and the black bill is a relatively long and straight. Non-breeding adults have a bi-coloured bill, reddish at the base with a black tip and a line through the middle.

More information

Conservation efforts

Black-billed gulls evolved to breed on weed-free shingle islands and banks on braided rivers. Their numbers have been declining rapidly for reasonably well-understood reasons outlined here.  Most conservation work has been to clear islands of weeds, create islands suitable for breeding birds (primarily high enough to withstand floods), reduce predator numbers through trapping, and install signs to deter people from disturbing them. Meanwhile, research into their genetics and population movements is ongoing. Some documents below are bird counts, while others are reports on population trends.