Adult Moreporks exhibit a variable plumage with numerous phases. The facial disc is dark brown with a light chamois border. The thin eyebrows are whitish. The upper parts are dark brown with spots and chamois-ochre stripes on the head, neck and mantle. Wings and scapulars have chamois-cinnamon or whitish dots. The primaries, secondaries and tertials are dark brown with thin chamois-cinnamon stripes. The tails is dark brown with thin ochre or chamois bars. The throat and the upper breast vary from brownish white to light brown with numerous dark chocolate-brown stripes. The rest of the underparts are covered with ocellated white feathers that have a dark terminal bar. The iris is either bright yellow or brownish yellow while the talons are brown or blackish.
The song is characterised by a diagnostic, yet variable from one individual to another, double note. It can be transcribe as "more-pork", but also, albeit less precisely, as "quore-quo". These notes are repeated after a pause than can last a few second although sometimes the intervals can be shorter. During the breeding season, on can also hear a vibrating and high-pitched "cree-cree".
Moreporks are are found in forests and farmland. They can also be seen in urban areas and plantations. This species has colonised virtually all altitudes, from sea level to the upper tree line.
Moreporks exhibit a similar behaviour to the Boobook Owl found in Australia. Birds are usually seen at dusk when they begin hunting for insects from a well-exposed perch. During the day, Moreporks are often mobbed by smaller birds and they spend most of the day resting in perches hidden behind dense foliage.
Moreporks start feeding at dusk, before complete darkness. Their staple prey is weta, a giant grasshopper-like flightless insects (Stenopelmatids). Moths, beetles and spiders are also an important part of the Morepork's diet. Two hunting methods a commonly used: either the prey are capture on the ground as the owl pounces from its perch or they are chased in the air. All prey are caught in the talons. Studies of regurgitation pellets in urban areas provide a good indication of their annual diet: it has been discovered that moths represent a sizeable chunk of the diet all year round while beetles and spiders play a less important role. Moreporks aslo feed on lizards, small birds (especially house sparrows), rats, mice and bats.
Egg-laying starts at the beginning of October, but only comes into full stride in November. The Morepork nests in tree hollows or dense Asteliacea tussocks. the nest can also be in an exposed place, on a tree fork or even in a small hollow on a old sparrow nest. Next boxes are sometimes used. The territory around the nest is quite vast and can measure between 4 to 8 ha. The brood usually consists of 2 to 3 round white eggs. They are laid at two-day intervals and incubated by the female only during 30 to 31 days. The male spends its time providing food for the incubating female. One the chicks have hatched, the pair both feed them. The young leave the nest after 34 days but will still benefit from parental help. Juveniles reach sexual maturity at the end of their first year, but will male only mate when they are two years old and female when they are three year old.
The Morepork in a New Zealand endemic. It is found in the North Island and its neighbouring islands (Little and Great Barrier, Three Kings and Kapiti). It also occurs in the South Island and on Stewart Island. Two subspecies live in Norfolk and Lord How islands. Three subspecies are officially recognised: N. n. novaesselandiae (New Zealand mainland, as well as Stewart, Three Kings, Kapiti, Little Barrier and Great Barrier islands), N. n. undulata (Norfolk Island) and N. n. albaria (Lord Howe Island, though to be extinct).
The N. n. novaesselandiae subspecies is locally common in New Zealand where it is widespread. It is found in farmland, urban areas (especially Christchurch), parcs and plantations of exotic trees. The N. n. albaria subspecies on Lord Howe Island is though to be extinct since the 1950s - it could not cope with the competition from introduced owls. The N. n. undulata subspecies found on Norfolk Island is endangered. Protection measure have been taken and 2 N. n. novaesselandiae males have been introduced to try and boost breeding. As the whole the species is not considered to be under threat.