Also used in some sources as Apteryx australis or Apteryx bulleri (before the year 2000, and some till now), the North Island brown kiwi (Apteryx mantelli) is an endangered species of kiwi bird found in the wild on New Zealand’s North Island, one of three subspecies of brown kiwi (the others being the Okarito brown kiwi and the Little Barrier Island brown kiwi).
It is an elusive nocturnal forest bird, and despite its gentle nature, it can inflict a nasty bite with its large beak if it feels threatened.
Apteryx mantelli, like other species of kiwi, is a nocturnal bird that typically grows to be about 15 inches long with their short, broad wings making them incapable of flying.
North Island brown kiwi occurs in two distinct populations; one in the northern half of the island, and another on the Kermadec Islands, which are considered an outlying part of the New Zealand territory.
The North Island brown kiwi or Apteryx mantelli, is endemic to New Zealand and belongs to the Haast Tokoeka group of the family Apterygidae. Unlike most other species of kiwi, this bird is nocturnal and mainly eats invertebrates such as large insects, spiders, snails, and earthworms.
When they are not eating they will be found in hollow trees where they build nests with soft dry leaves. They also dig burrows into hillsides for sleeping during the day.
At night they fly from their roosts to hunt for food up to 8km away from their nest site before returning home at dawn. It takes them a year to reach maturity but can live up to 20 years if conditions are good and they can evade predators such as cats, stoats, and dogs.
North Island brown kiwi scientific name
The scientific name of the North Island brown kiwi bird is Apteryx mantelli. Although it was formally referred to as Apteryx australis or Apteryx bulleri before the year 2000, today, some sources online still refer to the brown kiwis with these names.
Range and habitat
Brown kiwis live on the North Island of New Zealand and have short, stiff bills to comb through the ground for bugs. Kiwis are nocturnal and come out at night to hunt. They spend most of their time in forests, but they have also been spotted on agricultural land and in shrubland.
Brown kiwis can be found between sea level and 2,600 meters high. The brown kiwi is classified as a threatened species due to human encroachment into their habitat. As a result, there are now only about 3,000 left in the wild.
One conservation measure has been to establish predator-free areas where many brown kiwis were released after being rehabilitated from injuries. There is hope that these conservation efforts will help with population growth and protect this beautiful bird from extinction.
North Island brown kiwi size and weight
The North Island brown kiwi are stout birds, growing up to be around 18 to 24 inches in height (1.5 to 2 ft), females weigh around 2 to 3.9 kilograms (4.5 to 8.5 pounds) more than males that weigh around 1.4 to 3.2 kilograms (3 to 7 pounds).
Feathers and plumage
The North Island brown kiwi has long, narrow feathers with very distinctive plumage. Males have longer, darker and stronger plumage than females.
Males have a dark brown head with dark chestnut-brown plumage on the back and wings, light buff-brown underparts, and a dark mask around the eye. Females are paler and their plumage is generally browner overall. They also lack the black mask of males and have slightly lighter feathers.
A kiwi’s feathers are composed of keratin, which is the same substance as in human hair and nails. At intervals during its lifespan, a kiwi will need to completely shed its feathers so they can be replaced by new ones. This process, called molting, happens during the winter months when food is most plentiful.
Feathers grow at a rate of about 3cm per year until the bird has grown too large for them. In the months before molting, a kiwi’s growth slows down or stops altogether. During this time it eats less than usual and focuses on growing new feathers from follicles near the skin surface.
When it feels that its old feathers have become too stiff or heavy to use comfortably, it will molt them all simultaneously – often over a period of just one day. As with many other birds, feather molt usually occurs once each year and typically lasts from one to two weeks.
The North Island brown kiwi dig out a small hollow and either use leaves to line it or gather plants and grasses on top of it. They can be found in lowland forests and occasionally make use of artificial burrows in highland tussock grasslands. The incubation period is estimated to last up to 91 days.
Diet and foraging
The North Island brown kiwi birds enjoy an exceptionally varied diet of beetles, worms, crayfish, snails, fruits, insects, and berries. As the bird forages by repeatedly plunging it into the leaf litter of the forest floor to find food, its unique bill is used to sniff out prey.
Sounds and vocal behavior
Kiwi derives its name from the male’s ringing call. Females respond with a croaky sound resembling the noise caused by a long-rusty barn door being pulled open. The sounds are thought to alert members of the pair to stay in the same territory and stay in contact while searching for food in different locations.
There are many distinct growls, grunts, and hisses that members of both sexes will make, as well as audible snuffling as they hunt for food. A potential cause of the bird’s snuffling may be due to a valve located behind the nostrils, which, if open, prevents the animal from inhaling dirt and debris as it pecks around the ground.
Kiwis are usually born in pre-existing nests, so the location is long-established and concealed. The female lays a single giant egg, around 15% of her weight. Producing these large eggs causes the female to use a lot of her energy and may be exhausting for her. It takes female birds about 25 to 36 days between laying their first and second egg.
After that, the female leaves the male to incubate the eggs for 68 to 91 days. Kiwi chicks lack egg teeth and must kick their way out of the shell with their feet. As full-grown chicks, they resemble miniature versions of adults.
The age when most species are able to live completely independently is four weeks old, but they don’t reach their adult size until they are 18 to 20 months old.
The North Island brown kiwi lives up to 20 years in the wild and up to 50 years in captivity.
Movements and migration
During the summer months, North Island brown kiwis can be found in their small home range along the North Island of New Zealand. They eat mostly plants and insects, but will also eat birds.
As winter approaches they migrate to the South Island of New Zealand, where they spend their winters eating the plants and insects that are native to that area. In some cases, however, these kiwis might return back to the North Island in time for the summer months.
Diseases and threats
The North Island brown kiwi is endangered due to predation by rats and stoats. Cats, dogs, pigs, goats, deer, and domestic livestock are also predators of the North Island brown kiwi. Habitat loss is also a problem for this species as their preferred habitat has been steadily decreasing since European arrival in the area.
In 1996, there were around 35,000 North Island Brown Kiwi birds, but in 2006, the population has reduced to around 20,000. It is reported that the average number of kiwi chicks that survive to adulthood is only 5%. Active pest management zones, for example, may increase brown kiwi survival rates on North Island.
Conservation and management
The IUCN Red List rates North Island brown kiwi as Vulnerable, with the greatest threat coming from predators such as dogs, cats, and stoats. where mammalian pest control is not performed, 94% of chicks die before breeding. Thanks to the ongoing pest control, Tongariro has been able to almost double the population of adult kiwi since 1998.