New Zealand robins and tomtits resemble British robins, but the two groups are not closely related. The New Zealand species belong to the Australian–New Guinean family Petroicidae.
Robins and tomtits have large heads, short necks, round bodies and an upright stance. They have short bristles around the bill. Robins have long legs, and are larger than tomtits. All are insectivorous. The oldest known bird lived 16 years, but their life expectancy is three years.
North Island robin
North Island robins or toutouwai (Petroica longipes) are the largest of this group, 18 centimetres long and weighing 23 grams. They are darkish grey, with uneven white-grey underparts up to the chest, and a white dot above the bill. They feed mainly among leaf litter, collecting larvae, insects, worms and spiders, some of which they hide nearby. The male and female of a pair steal food from each other’s hiding places.
Feeding on the ground makes them vulnerable to predators, and their nests are easily accessible – so the species has disappeared from many areas. They are still found in forests of the western and central North Island, and on Little Barrier and Kāpiti islands – and they have been reintroduced to some sanctuaries where predators are controlled.
South Island robin
The South Island robin (Petroica australis) is similar to the North Island species, but is pale yellow underneath and more evenly dark on top. The male has a distinct boundary between the dark grey and pale yellow on its upper chest.
There are two subspecies – South Island and Stewart Island robins.
Black robins (Petroica traversi) are endemic to the Chatham Islands. They made a dramatic recovery from a low point of five birds in 1979, thanks to skilled management by staff of the New Zealand Wildlife Service and the breeding prowess of one female, Old Blue. The birds were moved to better habitats, and eggs were given to tomtits to raise so the robins would keep laying. By 2020, there were about 250 birds.
New Zealand tomtit
The New Zealand tomtit or kōmiromiro (Petroica macrocephala) has five subspecies – one on each of the North, South, Chatham, Snares and Auckland islands. They have a dark head, throat and back – black in males, brown in females – with white underparts. Males have a sharp dividing line across the breast, tinged with yellow in the South Island subspecies. Adults have a small white dot above the bill. The Snares Island subspecies is completely black. On average, tomtits measure 13 centimetres and weigh 11 grams.
The female builds a bulky nest in a tree fork, and is fed by the male while she incubates the eggs – then both feed the chicks. They raise up to three broods a year. Their diet is a wide range of invertebrates, which they catch by scanning a wide area and pouncing on prey. Their call, which has been compared to a squeaky wheelbarrow, sounds like ‘tea-oily-oily-oh’.