A kiwi population survey conducted in the Forest Lifeforce Restoration Trust’s sanctuary in the Maungataniwha Native Forest has yielded an adjusted male call rate of 2.53 an hour. This is high by Hawke’s Bay standards and compares favourably with rates of 0.5 an hour just across the Waiau River in unmanaged parts of Te Urewera National Park.
The result shows a small but statistically insignificant increase over the baseline result from 2015 of 2.27 calls an hour at six listening sites used in both surveys.
National kiwi survey protocols were used to conduct the research. Sites were surveyed during the first two hours of darkness for three consecutive nights in May, with two people staffing each site.
The same methods and listening sites used in 2015 and 2016 were used this year to minimise between-year variation. One of the original 2015 sites was discarded because it was too exposed to wind.
This year the survey team measured the call rates of radio-tagged kiwi males and used the information to remove the effects of confounding variables from year-to-year abundance comparisons. This makes the call monitoring technique more precise and enables call count indices to be turned into density estimates if the size of listening areas can be measured (or estimated) reasonably accurately.
It is thought the listening areas at Maungataniwha probably averaged about 120 ha in size, giving an approximate average density of one male per 20 ha. The 120 ha assumption will be tested in 2018 by broadcasting calls at ‘kiwi volume’ in various places at Maungataniwha and measuring the distances at which they can be heard.
“The Trust team members behind the Maungataniwha Kiwi Project, Barry Crene and Pete Shaw, should be very pleased with this result,” said Trustee Dr John McLennan who conducted the survey and interpreted its results.
“A stable population is a significant achievement in its own right, given the difficulty managers have had maintaining and growing kiwi populations in other parts of the lower North Island. The kiwi management and predator control programme at Maungataniwha has stopped the population declining and possibly generated a small, but statistically insignificant, amount of growth.”
The call count survey measures the abundance of the adult kiwi population at specific listening sites and not the total number of birds on the property. Many of the juveniles released at Maungataniwha over the past two years are still too immature to hold territories and breed. Their contribution to population recovery will only become evident in the next 12-24 months when they join the adult population and begin to call.
The Maungataniwha Kiwi Project run by the Trust is one of the most prolific and successful kiwi conservation initiatives in the country and part of the national kiwi breeding programme known as Operation Nest Egg. Adult male kiwi are fitted with radio transmitters to enable volunteers to retrieve their eggs, which are then taken for artificial incubation. The resulting chicks are raised in a special crèche or captive facility until they are large enough to fend for themselves in the wild.
Over 11 seasons between 2006 and April 2017 the Maungataniwha Kiwi Project has released 184 kiwi back into the forest.
All these have been microchipped so that they can be identified.
Fully-fledged chicks released back into the forest have an approximately 70 percent chance of survival. This survival rate contrasts starkly with the five percent chance they have of making it to adulthood if hatched in the bush and left unprotected against predators.
Dr McLennan was instrumental in establishing the kiwi conservation programme on the Puketukutuku Peninsula on Lake Waikaremoana, now managed by Tuhoe, where kiwi are now approaching pre-human levels of abundance with survey readings of as many as 30 calls an hour.
Despite the survey findings Maungataniwha remains well below its kiwi carrying capacity, Dr McLennan said. “We reckon our sanctuary area is home to about one-sixth of the number of kiwi it could potentially support.
Counts at 30 new sites in 2016 and 2017 indicated only half the number of kiwi than at long-term monitoring sites so we are always careful not to provide an inflated view of average kiwi abundance across the whole property.
“That said, the population here is now one of the most significant in the lower North Island. It has endured while others near it have declined or failed altogether. Its importance will grow even more in coming years, both as an anchor for kiwi in Hawkes Bay, and as a source of kiwi for release elsewhere. Hawkes Bay, and the eastern race of NI brown kiwi, is fortunate to have Maungataniwha within its rohe.”
The Maungataniwha kiwi survey team has been interested to learn that tagged male kiwi there do not call very often, and that average call rates of just 1.0 or 2.0 per hour result from the combined efforts of several different individuals. Hawke’s Bay unmanaged kiwi population densities are usually lower than other places on the North Island. In Northland call rates of six to 10 an hour are common.
In addition to the Maungataniwha Kiwi Project the Trust runs a series of native flora and fauna regeneration projects. These include a drive to increase the wild-grown population of Kakabeak (Clianthus maximus), an extremely rare type of shrub, and the re-establishment of native plants and forest on 4,000 hectares currently, or until recently, under pine.