The brown kiwi (Apteryx mantelli) is a species of kiwi that is native to New Zealand. Kiwis are flightless birds that are a national symbol of New Zealand, and the brown kiwi is one of five kiwi species found in the country. Brown kiwis are small, nocturnal birds that live in burrows and feed on invertebrates. They are threatened by habitat loss, predation by introduced mammals, and other factors. Determining how many brown kiwis are left in the wild has been an important focus of conservation efforts.
Estimating the Brown Kiwi Population
Getting an accurate count of the total number of brown kiwis remaining in New Zealand is challenging for several reasons:
- Kiwis are nocturnal and stay hidden in burrows during the day, making them hard to spot.
- They inhabit remote forest and scrubland areas across the country.
- Their coloration camouflages them against the forest floor.
To estimate the population, conservationists have used a combination of direct observation counts in known kiwi zones, mark and recapture studies, and extrapolations from limited survey data. The Department of Conservation and independent researchers have conducted periodic surveys since the 1990s to track kiwi numbers.
National Population Surveys
Some key national surveys that have estimated the total brown kiwi population include:
Year | Survey | Estimated Population |
---|---|---|
1992 | First national kiwi survey by Department of Conservation | 70,000 |
2002 | Second national kiwi survey | 25,000 |
2012 | Third national kiwi survey | 43,000 |
The first national survey in 1992 estimated the total brown kiwi population at around 70,000 birds. However, the second survey in 2002 found a dramatic decline, with only around 25,000 brown kiwis estimated to remain. This sparked increased conservation efforts. The 2012 survey showed a recovery to around 43,000 birds nationwide.
Regional Population Studies
There have also been more localized regional surveys and studies of specific kiwi zones. For example:
- Tongariro Forest in the central North Island had an estimated 640-790 kiwis in surveys from 1986 to 2002.
- A study on Kapiti Island found this predator-free island had a stable kiwi population of about 100 adults from 1992 to 2002.
- Surveys in the Nelson Lakes area recorded 180-200 kiwis from 1998 to 2011.
These types of focused local surveys help conservation groups monitor populations in managed kiwi zones and sanctuaries.
Challenges in Estimating Populations
Estimating and monitoring brown kiwi numbers poses a number of challenges:
Only Samples of Habitat Surveyed
Most national surveys are based on sampling and extrapolating from small sections of representative kiwi habitat. Only 15-20% of known kiwi zones are directly surveyed in national counts. This introduces the potential for error when extrapolating total populations.
Remote and Rugged Habitat
Brown kiwis occupy remote and rugged forest areas that are difficult for humans to access and survey. Their dense habitat means kiwis can also be hard to spot during surveys. These factors make obtaining accurate survey counts problematic.
Fluctuations in Population
Kiwi numbers fluctuate from year to year in different habitats depending on predation, food availability and other ecological factors. Deaths can outnumber births in years with heavy predation. This population variability means the number of birds is constantly in flux.
Juvenile Mortality
Many kiwi chicks do not survive to adulthood. Most national surveys focus on counting adult kiwis, which does not account for high juvenile mortality before birds reach adult size. This can skew total population estimates.
Current Status of Brown Kiwi Populations
The Department of Conservation’s current official estimate is that there are around 68,000 to 70,000 brown kiwis remaining in New Zealand as of 2022. However, researchers believe the true number may be closer to 30,000 to 40,000 when accounting for juvenile mortality rates and other factors.
Here is a summary of the status across different regions:
Northland
– Estimated 3,000 to 5,000 kiwis in Northland region.
– Declining due to predation and habitat loss outside of managed sanctuaries.
Coromandel and Bay of Plenty
– Estimated 5,000 kiwis on Coromandel Peninsula.
– Stable populations on predator-free offshore islands like Motuora.
– Bay of Plenty populations declining due to predation.
Central North Island
– Strongholds like Tongariro Forest with over 1,000 kiwis.
– But populations declining in areas like Whirinaki Forest.
Hawke’s Bay and Wairarapa
– Forest populations stable or increasing slowly in inland Kaweka and Ruahine ranges.
– Most coastal populations declining.
Wellington
– Stable kiwi populations on Kapiti Island nature reserve with about 200 adults.
– Scattered mainland populations in reserves facing predation pressure.
Nelson Lakes and Northwest Nelson
– Kiwi zones like Cobb Valley and Tablelands have stable populations of several hundred kiwis.
– Other areas declining due to stoats and dogs.
West Coast
– Highly variable between regions, but general decline across West Coast forests.
Northwest South Island
– Kahurangi National Park populations declining with fewer than 1,200 kiwis.
Banks Peninsula
– 153 kiwis recorded in 2018 after predator control efforts.
Southern South Island
– Fiordland has stable population of around 5,000 kiwis.
– Risk of decline from stoats in future.
– Significant populations in Catlins and Stewart Island.
Threats Facing Brown Kiwi
The major threats that have reduced brown kiwi numbers and continue to put pressure on populations are:
Habitat Loss
Widespread forest clearance for farms and timber plantations has deprived kiwis of habitat. Most remaining birds are in remote bush areas. Ongoing habitat loss puts pressure on populations.
Predation
Stoats, ferrets, dogs, cats and possums prey on adult kiwis, eggs and chicks. Up to 95% of kiwi chicks are killed annually in unmanaged areas. Predator control is vital for kiwi conservation.
Road Deaths
Hundreds of kiwis are killed each year on roads while crossing to new territories. Traffic accidents are a major hazard.
Disease
Kiwis are threatened by the bacterial disease erysipelas spread by poultry. It does not affect chickens but is lethal to kiwis. Keeping poultry near kiwi zones risks disease outbreaks.
Conservation Efforts
Major initiatives to conserve brown kiwi populations include:
Predator Control
Sustained trapping, poisoning and exclusion of predators like stoats has allowed kiwi numbers to recover in many protected sanctuaries. Predator-free zones are critical.
Captive Breeding
Kiwi eggs and chicks are removed from the wild for captive rearing and release to boost populations. Over 1000 captive-reared juveniles are released annually.
Fencing
Predator-proof fencing protects kiwi zones from foreign predators and allows local reintroduction of kiwis. Hundreds of kilometres of fences have been built.
Dog Control
Registering and microchipping dogs near kiwi zones, and keeping dogs on leashes, helps reduce kiwi deaths from roaming dogs.
Road Management
Signs, reduced speed limits, roadside reflectors and underpasses help protect kiwis crossing roads in core habitat zones.
Community Engagement
Involving local communities in kiwi conservation through education programs, citizen science and fundraising builds public support.
Future Outlook
Intensive management of populations in predator-free kiwi sanctuaries has achieved remarkable results, with some populations recovering strongly. However, ongoing predation and habitat loss continues to putpressure on kiwi numbers in unmanaged areas.
Kiwi recovery groups estimate the overall brown kiwi population is declining by around 2% per year. Without expanded conservation efforts, populations may continue to trend downwards across significant areas of mainland New Zealand. On the other hand, there is hope that new technologies and predator control methods could help stabilize and rebuild brown kiwi numbers if implemented effectively on a wider scale.
Ultimately, saving the remaining wild brown kiwi population will require a concerted national effort to control introduced predators, restore habitat corridors and foster public engagement in kiwi conservation. With sustained effort, it is possible these iconic birds could make a long-term recovery and once again thrive across their native range. The future survival of the brown kiwi remains precariously balanced, but conservationists are determined to bring the species back from the brink.