Brown Kiwi Facts | New Zealand Wildlife Guide

Brown kiwis (Apteryx australisare) are pear-shaped, flightless birds that possess rudimentary wing structures.

Kiwis possess a strong sense of smell and track down prey using their nostrils, which are located on the tips of their bills. Their small eyes result in poor vision, but well-developed ears that are visible through their feathering aid them.

Physical Characteristics

• A small head and a slender, elongated bill with catlike whiskers at its base.
• Distinct sexual dimorphism between males and females. Males typically weigh between 5 and 7 pounds and measure 18 inches in height, with a bill length of 3.7 to 4.1 inches. Females weigh between 8 and 9 pounds, are about 20 inches tall and have a bill length of 4.3 to 4.7 inches.
• Plumage consists of very soft, fine feathers, which are hairlike in texture.
• Feathers are a reddish-brown color streaked with darker brown and black.
• Powerful legs and sharp claws, which they use to quickly flee predators and fight enemies.
• Their body temperature is much higher than most birds and is similar to humans, at 100°F.
• Terrestrial creatures, their dense bones are filled with marrow rather than hollow, as with other birds.
  
  

Feeding Habits

Kiwis are nocturnal creatures and emerge to hunt about a half hour after sunset. They stealthily walk through the brush, using their sensitive bills to tap the earth while sniffing. After sensing an underground insect or earthworm, they stab their beak repeatedly into the earth before plucking up their prey. They also consume berries and fruit fallen from trees, crayfish, spiders and snails.

Habitat & Behavior

Kiwis are found primarily in the subalpine scrublands and alpine regions of northwest New Zealand. Kiwis take shelter in burrows, which they excavate from the soil several weeks before using. This period allows for moss, earth and plant matter to naturally redistribute and camouflage the burrow from predators. Each bird may have up to 100 different shelters within its territorial range, and it typically uses a different one each day. Kiwis are shy and timid by day and do not leave their burrows unless forced out by danger. However, come nightfall, they become extremely aggressive.

In the most densely populated areas of the forests, it is not unusual to find four to five kiwis located within 1 square kilometer. These birds are exceptionally territorial, and breeding pairs aggressively guard their nesting areas, which are typically about 62 acres in size. It is not fully known how these diminutive birds manage to police their large areas of land, but kiwis do call to one another, which may play a key role. Males are particularly fierce when defending their territory, and fights with intruders may result in fatalities. However, death or injury during these encounters are uncommon, and male kiwis generally do not assume another’s territory until the occupant is crippled or dies.

Reproduction

Kiwis are strictly monogamous birds—they usually join in pairs for two to three consecutive mating seasons and may stay together for life. Breeding takes place during late autumn, and the gestation period lasts about one month. Egg production is an exhausting process for the females, as their eggs may reach one-fifth of their body mass. Females cannot eat during this time because the egg occupies most of their body cavity. Instead, the female relies on reserves of fat, which she stored during the five months before fertilization, to create the nutrient-rich, giant egg.

The gestation period is a painful time for the female, whose movement becomes severely restricted. To counteract the discomfort and inflammation she experiences, the mother takes to soaking her aching abdomen in cool puddles near her burrow. Males incubate the eggs once laid. The father leaves the burrow only for a few hours each night to hunt while the mother stands guard.

Hatching occurs between 75 and 85 days, during which time the chick spends two to three days attempting to break free from its shell. In the first three days of life, the chick’s stomach is so bloated by the yolk sac that it is unable to move. The parents abandon the chick after it hatches, and in less than 10 days’ time, the young kiwi is foraging outside the burrow. The self-reliant chick may hunt for food during the daytime until it is 6 weeks old, when it becomes exclusively nocturnal.

Animals such as ferrets and stoats prey upon many kiwi chicks. Once the chicks reach a weight of 1.75 pounds at between 17 and 20 weeks, they are able to defend themselves. Kiwis grow until they reach the age of 6, but males may reach sexual maturity as early as 14 months old. Female kiwis may become sexually mature at 2 years of age, and unlike most birds, have two functional ovaries as opposed to one.

Conservation

Because of the kiwi’s reclusive nature and nocturnal habits, not many New Zealanders encounter their national mascot in the wild. Due to the bird’s elusiveness, the severe decline in the kiwi population has gone largely unnoticed. About 1,000 years ago, the population of kiwis roaming the forests of New Zealand was approximately 12 million. In 1996, biologists found this number had plummeted to fewer than 70,000. Until protective measures were put into place, the kiwi population fell by 6 percent each year, mainly due to predation from non-native species such as dogs, cats, ferrets and stoats introduced by European settlers in the late 1800s.

The Kiwi Recovery Group was established in 1991, and this program’s initiatives increased the survival rate of kiwi chicks from 5 percent in 1991 to 60 percent in 1998. Predator control and monitoring have been the most crucial success factors, but efforts in advocacy, research, habitat protection and captive breeding and reintroduction have also spurred population growth. Kiwis are hardy creatures: they are able to endure severe environmental conditions, are resistant to most natural illnesses, and females can lay up to 100 large eggs over the course of their lifetimes. It is hoped that continual conservation efforts will allow the kiwi to repopulate the regions where it once flourished.

Header Credit: Judi Lapsley Miller [CC BY 4.0] via Wikimedia Commons

Know Before You Go