Kiwi are true night birds. They spend the day hidden in dens and come out after dark to work the forest floor. That makes them unusual, because the great majority of birds are active by day.1Genome Biology. Kiwi genome provides insights into evolution of a nocturnal lifestyle To live in the dark, kiwi have swapped the eyesight most birds depend on for a good nose, a touch-sensitive bill and sharp ears.
How Rare a Night Bird the Kiwi Is
Fewer than 3% of bird species are active at night.2Genome Biology. Kiwi genome provides insights into evolution of a nocturnal lifestyle Kiwi are in that small group, and they are the only nocturnal ratites, the group of flightless birds that includes emus and ostriches.3Genome Biology. Kiwi genome provides insights into evolution of a nocturnal lifestyle New Zealand’s extinct moa were also ratites, but they were active by day.4Genome Biology. Kiwi genome provides insights into evolution of a nocturnal lifestyle So kiwi took up a way of life almost none of their relatives share. Kiwi are flightless, run on the ground and live on the forest floor,5PubMed Central. Kiwi Forego Vision in the Guidance of Their Nocturnal Activities so their entire active life happens at ground level, in the dark.
Most birds are daytime animals because they rely heavily on sharp vision, which works best in daylight. A few other night birds, such as owls, kept big eyes. Kiwi took a different route.
Being active at night doesn’t mean a visitor will see one just by going out after dark. Wild kiwi are shy and keep to dense cover, and a bright torch on a forest track usually just sends one away. The best sign of a kiwi nearby is often sound, such as a call or the faint rustle of a bird working through leaf litter.
A Kiwi’s Night From Dusk to Dawn
Kiwi seldom leave their dens until it is fully dark, 30 to 90 minutes after sunset.6New Zealand Journal of Ecology. Range size and denning behaviour of brown kiwi, Apteryx australis mantelli, in Hawke’s Bay, New Zealand When a bird does come out, it usually emerges quietly but suddenly, then sniffs around the entrance for up to a minute before moving off.7New Zealand Journal of Ecology. Range size and denning behaviour of brown kiwi, Apteryx australis mantelli, in Hawke’s Bay, New Zealand
Most of the dark hours go to finding food. Kiwi feed mainly on soil and surface-dwelling invertebrates like worms and insect larvae.8PubMed Central. Kiwi Forego Vision in the Guidance of Their Nocturnal Activities Nearly all of them probe into leaf litter in forest, or into matted grass roots in pasture.9New Zealand Journal of Ecology. The secret life of wild brown kiwi: studying behaviour of a cryptic species by direct observation Most also probe into the soil, and soil probes produce almost half of their catches.10New Zealand Journal of Ecology. The secret life of wild brown kiwi: studying behaviour of a cryptic species by direct observation A small share of prey, under 3%, is snatched straight off the surface with rapid bill tapping.11New Zealand Journal of Ecology. The secret life of wild brown kiwi: studying behaviour of a cryptic species by direct observation
A probing kiwi doesn’t run or dash. It walks slowly, stopping often to push its long bill down into the litter or soil. It may sink the bill deep, pull out, and move a step to try again if nothing turns up. Because the bill is long and slender, it reaches food well below the surface that a bird looking from above would never know was there.
Calling and checking territory fit in between feeding bouts. The night ends with the search for a safe place to sleep: in the half-light of dawn kiwi stop feeding and choose a den for the day.12New Zealand Journal of Ecology. Range size and denning behaviour of brown kiwi, Apteryx australis mantelli, in Hawke’s Bay, New Zealand
Finding Food in the Dark Without Good Eyes
The kiwi eye is unusually small for a night bird, though its retina is built for low light.13Genome Biology. Kiwi genome provides insights into evolution of a nocturnal lifestyle Kiwi have also lost colour vision.14PubMed Central. Kiwi genome provides insights into evolution of a nocturnal lifestyle Wild brown kiwi show no obviously sight-guided behaviour,15Animal Behaviour. Tactile senses and foraging in birds, with emphasis on kiwi: a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand so vision isn’t the sense they rely on to find food, and the eye has been allowed to shrink.
Smell does much of the work. Kiwi have smell-processing brain areas proportionately larger than any other bird compared.16PubMed. Anatomical specializations for enhanced olfactory sensitivity in kiwi, Apteryx mantelli They use scent to forage and possibly to communicate with each other.17PubMed. Anatomical specializations for enhanced olfactory sensitivity in kiwi, Apteryx mantelli Their nostrils sit near the tip of the bill, unlike other birds. Most birds have nostrils at the base of the bill, far from the ground while feeding. A kiwi can sniff at the exact spot where its bill enters the soil, sampling scent right where the food might be.
Touch matters too. The bill tip has clusters of touch sensors in tiny pits.18PubMed Central. The Anatomy of the bill Tip of Kiwi and Associated Somatosensory Regions of the Brain: Comparisons with Shorebirds The brain region handling touch from the face is enlarged, as in sandpipers.19PubMed Central. The Anatomy of the bill Tip of Kiwi and Associated Somatosensory Regions of the Brain: Comparisons with Shorebirds Ibises find buried prey by touch alone, but kiwi combine touch with smell.20Animal Behaviour. Tactile senses and foraging in birds, with emphasis on kiwi: a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand Whisker-like bristles at the bill base probably help them feel their way on the ground at night.21PubMed. Facial bristle feather histology and morphology in New Zealand birds: implications for function They look like cat whiskers, but they are modified feathers, and many birds have such bristles. They are thought to sense touch rather than act as a main guide.
Hearing fills in the rest. Wild kiwi lift their heads at sounds and sniff toward them.22Animal Behaviour. Tactile senses and foraging in birds, with emphasis on kiwi: a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand Their inner ear devotes extra space to sounds of about 4 to 6 kHz,23PubMed Central. Evidence for an Auditory Fovea in the New Zealand Kiwi (Apteryx mantelli) so their ears seem tuned to a particular range, possibly prey or calls.
Where Kiwi Spend the Day
About two-thirds of daytime dens are natural cavities under roots, fallen branches or thick plants, or inside rotting logs.24New Zealand Journal of Ecology. Range size and denning behaviour of brown kiwi, Apteryx australis mantelli, in Hawke’s Bay, New Zealand The other third are burrows the birds dig themselves.25New Zealand Journal of Ecology. Range size and denning behaviour of brown kiwi, Apteryx australis mantelli, in Hawke’s Bay, New Zealand Den choice does not change consistently with season, so warmth or moisture seem unlikely to be the main reason.26New Zealand Journal of Ecology. Range size and denning behaviour of brown kiwi, Apteryx australis mantelli, in Hawke’s Bay, New Zealand Hollows and burrows keep the bird out of sight all day, and a kiwi may pick a different den on different days.
If you do find a burrow, leave the entrance alone and keep dogs away. Don’t try to look inside or wake the bird. In managed areas, report sightings to local conservation staff.
Why Kiwi Became Night Birds
Kiwi probably avoided New Zealand’s many large daytime birds of prey by being nocturnal, drab and secretive.27New Zealand Journal of Ecology. Size matters: predation risk and juvenile growth in North Island brown kiwi (Apteryx mantelli) Brown, streaky plumage blends with leaf litter and shadow, so a resting bird is hard to pick out.
They had few if any night predators.28New Zealand Journal of Ecology. Size matters: predation risk and juvenile growth in North Island brown kiwi (Apteryx mantelli) Before humans brought mammals, almost nothing threatened a kiwi in the dark, so night was a safe time to be out in the open.
Kiwi also live a lot like small mammals. They have the smallest body among flightless ratites, the lowest metabolic rate of any bird, and an insect-type diet.29PubMed Central. Kiwi genome provides insights into evolution of a nocturnal lifestyle That means they resemble early night-active mammals that were small, insect-eating and slow-burning.30PubMed Central. Kiwi genome provides insights into evolution of a nocturnal lifestyle Their senses parallel those of forest-floor night mammals, shaped by the same challenges.31PubMed Central. Kiwi Forego Vision in the Guidance of Their Nocturnal Activities
The Dangers Kiwi Face at Night Today
Young kiwi are heavily hunted by stoats in their first four months.32New Zealand Journal of Ecology. Size matters: predation risk and juvenile growth in North Island brown kiwi (Apteryx mantelli) Once over about 800 g they are too big for stoats to kill.33New Zealand Journal of Ecology. Size matters: predation risk and juvenile growth in North Island brown kiwi (Apteryx mantelli)
Trapping programmes target stoats across kiwi areas, removing them before they reach chicks. Some groups also raise chicks safely until they pass the danger weight. Keeping dogs leashed protects adult kiwi, which dogs can kill easily.
Light may matter as well. Captive kiwi spend more time in dimmer areas, whatever the light colour.34New Zealand Journal of Ecology. Lighting trends reveal state of the dark sky cloak: light at night and its ecological impacts in Aotearoa New Zealand Kiwi call less on cloudy nights yet are not affected by moonlight, hinting that clouds reflecting town lights may matter.35Journal of Avian Biology. Temporal and environmental influences on the vocal behaviour of a nocturnal bird Near kiwi habitat, it makes sense to keep outdoor lights low and shielded.
How to See a Kiwi Awake
About a third of captive kiwi live in nocturnal houses with a reversed light cycle for visitors.36Animal Welfare. Survey of husbandry practices and captive environments for North Island brown kiwi (Apteryx mantelli) housed in facilities within and outside New Zealand The house is kept dim during visiting hours by day and lit at night, so the birds are active when visitors come.37Apogee Instruments. Nocturnal Enclosure for Kiwi Birds Some houses use dim lighting that mimics moonlight and floors of soil and leaf litter.38Apogee Instruments. Nocturnal Enclosure for Kiwi Birds
Inside, let your eyes adjust for a few minutes. The moonlight-like lighting means you may see only a shape at first. Look low, near the leaf litter, where a probing bird is most likely to be. Never use flash photography, and stay quiet, since kiwi rely on hearing.
In the wild, listening is the best approach. Male and female little spotted kiwi have clearly different calls.39Ibis. Vocal cooperation between the sexes in Little Spotted Kiwi Apteryx owenii Male calls suit defending territory and female calls suit keeping in touch with a partner.40Victoria University of Wellington. Whistling in the Dark: an Acoustic Study of Little Spotted Kiwi Pairs often call in duets.41Ibis. Vocal cooperation between the sexes in Little Spotted Kiwi Apteryx owenii A male’s call is shrill, a female’s lower and hoarser. Guided night walks use red or dim torches, and calls are often heard long before a bird is seen.