New Zealand tomtits resemble British robins, but the two groups are not closely related. The New Zealand species belong to the Australian–New Guinean family Petroicidae. Tomtits have large heads, short necks, round bodies and an upright stance. They have short bristles around the bill. All are insectivorous. The oldest known bird lived 16 years, but their life expectancy is three years.
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, and may be re-classified as a separate species (Petroica dannefaerdi). 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’.