The kiwi is New Zealand’s national symbol and a unique bird found only in New Zealand. Kiwis are flightless birds, so they cannot migrate in the traditional sense like many bird species that fly long distances to warmer climates for the winter. However, some kiwi populations do make small local migrations based on food availability and habitat conditions. In this article, we’ll explore what’s known about kiwi migration patterns and why they don’t migrate over long distances.
Kiwi Habitats and Geographic Distribution
There are five species of kiwi living in different parts of New Zealand:
- Great Spotted Kiwi – Occurs in the northwest of the South Island.
- Little Spotted Kiwi – Found in small regional populations scattered throughout the mainland.
- Rowi – A rare species from Okarito in northwest South Island.
- Tokoeka – Distributed in south and western parts of the South Island.
- Brown Kiwi – The most widespread and numerous species throughout northwest South Island, southeast North Island and offshore islands.
Kiwis are generally found in forests, scrublands, swamps, and subalpine areas where there is dense vegetation cover. Their geographic range extends over 1,000 miles from the subtropical northern tip of New Zealand down to the cool southern regions of the South Island. Across this range, habitats and climate conditions can vary significantly. Kiwis are well-adapted to cooler, wetter climates and cannot tolerate hot, dry conditions well.
Why Kiwis Don’t Migrate Long Distances
Most bird species migrate to escape harsh winters, find better food sources, or reach breeding grounds. Kiwis don’t face extreme cold winters or lack of food within their New Zealand habitats. New Zealand’s mild climate varies from subtropical in the north to cool temperate in the south. Winters are relatively mild, and summers are not hot. The vegetation and insect food sources kiwis rely on are available year-round across most of their range.
The main reason kiwis likely never evolved long-distance migration is that their flightless condition prevents them from flying thousands of miles between seasonal habitats. Kiwis are one of the few bird species in the world that are flightless. Their small vestigial wings are hidden under their hair-like feathers and serve no purpose in flight. Without wings, the only way kiwis could migrate is by walking or swimming, neither of which would be feasible over long distances or across oceans.
Interestingly, the kiwi’s closest relatives are emus and cassowaries – large flightless birds from Australia and New Guinea that also do not migrate. The common ancestor of these birds is thought to have flown but lost the ability over time in the absence of predators. In New Zealand’s isolated environment with few land mammals, losing flight was not a major disadvantage for kiwis. But it did preclude them from migrating vast distances like their flying cousins.
Local Migration Patterns
Although kiwis do not migrate long distances, some local populations do make small seasonal movements. These are usually altitudinal migrations where kiwis move to higher or lower elevations within their territory. Such movements are made in response to seasonal changes in climate, food availability, nesting conditions, and even high numbers of parasites.
For example, studies of great spotted kiwi populations in Northwest Nelson found they migrate seasonally between lowland wintering areas near sea level to breeding areas higher in the mountains around 1,500 feet elevation. In winter, they descended to the lowlands where winters were milder and food was still abundant. But they returned to subalpine and montane areas in spring to breed and nest in boulder fields that provided safe habitat for their eggs and chicks.
Rowi kiwis in South Westland have been found to migrate between beach habitats in winter to forests further inland for breeding in summer. Their movements coincided with peaks in insect populations in beach scrublands in winter versus greater protection and food in forests for rearing chicks in summer.
Not all kiwi populations migrate locally. But such movements allow some populations to adapt to seasonal changes in climate, food availability, breeding conditions, and predation or parasite pressure across their territories. Their movements are over distances of 20-40 kilometers typically, unlike the thousands of kilometers covered in typical bird migration.
Threats from Habitat Loss and Predators
While New Zealand’s environment supported flourishing kiwi populations for millions of years, habitat loss and predation by invasive mammals have caused dramatic declines since human settlement of the islands. It’s estimated there were 12 million kiwis before Polynesians arrived around 1280 AD. By the early 1900s when Europeans colonized, kiwi numbers had dropped to just 1 million. Today there are only around 68,000 kiwis left in the wild.
Deforestation and habitat modification have reduced and fragmented the forests and scrublands kiwis rely on for their territories. With flightlessness preventing long-distance dispersal to new habitats, local populations can become completely cut off and prone to dying out. Predation by dogs, cats, stoats, ferrets, rats, and possums introduced by humans have also devastated kiwi numbers, especially their eggs and chicks.
These threats make kiwis extremely vulnerable to extinction. Their long life span, few offspring, and lack of migration ability also limits their capacity to recover from population declines. Intensive conservation efforts are underway to control predators, restore and connect habitats, breed kiwis in captivity, and monitor wild populations. Careful management of migration routes and habitat corridors is also needed to allow kiwis to make their local seasonal movements where these occur.
Future Outlook
The kiwi has been resilient over eons of geological upheavals that created New Zealand’s rugged and isolated landscape. But human impacts within the past 800 years have pushed the iconic bird to the brink of extinction. While we now understand kiwi ecology much better, their populations continue to decline across most of their range, with the exception of a few sites where intensive management is focused. Even at those sites, kiwi survival remains precarious without continued conservation efforts.
All five kiwi species are classified as threatened or at risk of extinction. But some populations have shown the potential to recover in predator-free sanctuary sites. Ongoing work to control predators, restore habitats, expand sanctuary areas, and establish new populations gives hope that kiwi migrations will continue in pockets across their historic range. Perhaps future generations will still have the chance to see this national taonga making its humble seasonal wanderings across the New Zealand bush.
Conclusion
In summary, kiwis are unusual among birds for not migrating over long distances. Their flightless condition prevents the kind of migrations seen in flying species that traverse thousands of miles between seasonal habitats. However, some kiwi populations do make small local migrations of 20-40 km in response to seasonal changes in climate, food availability, breeding conditions, and parasite loads. These altitudinal migrations allow them to adapt to habitat conditions across their territories. While kiwis survived for millions of years in New Zealand’s isolated environment, recent human impacts have depleted populations down to critical levels. Careful conservation management is needed to protect local migration routes and help rebuild viable kiwi populations into the future.
