The challenges of counting kākāriki

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Counting green parakeets in an equally green forest can be something of a challenge even for the experts. But when those parakeets are as rare as our orange-fronted kākāriki, it’s important to get a good estimate of how many there are and whether numbers are increasing or decreasing.

Kākāriki on a branch
Kākāriki-rae-karaka. Image credit: Christopher Stephens

There may be less than 100 adult kākāriki-rae-karaka (orange-fronted parakeets) remaining on mainland New Zealand. They’re restricted to three valleys in the North Canterbury region and, because they’re often found on the ground and on low-level vegetation, they’re very vulnerable to introduced mammal predators, especially mustelids and rats.

Kākāriki-rae-karaka are the smallest of our parakeet species – about the size of a budgie with males only weighing around 40-50 grams. They’re found almost exclusively in beech forest with breeding possibly tied to beech masts when food is plentiful. Unfortunately, mammal predator numbers soar in beech masts, potentially leading to high levels of predation exactly when the birds are attempting to raise their young. Because females nest in tree cavities, they and their chicks are an especially easy target.

To help keep the species safe, many captive-bred birds have been translocated to predator-free islands. But the last time any of those birds were counted was 2009. Until recently, no-one knew how they were doing or whether their numbers were increasing.

Researchers Michael Skirrow, Adam Smith and Luis Ortiz-Catedral from the School of Natural and Computational Sciences at Massey University’s Auckland campus and the World Parrot Trust Oceania Conservation Program (Auckland) decided it was time to do a Kākāriki Count and recently published their results in the New Zealand Journal of Zoology.

Kākāriki-rae-karaka has been identified as one of nine critically endangered parrots in the Oceania region requiring further conservation research. For a long time we didn’t even realise that orange-fronted kākāriki were a distinct species and that hasn’t helped their conservation, as the researchers explain.

“Historically, this species was considered a colour morph of the yellow-crowned parakeet, due to the morphological similarities between the two species. However, research examining bill morphology, assortative pairing, call characteristics, comparative ecology and molecular systematics has provided sufficient evidence for the classification of the orange-fronted parakeet as a phylogenetically distinct species. The historical uncertainty surrounding the taxonomy of orange-fronted parakeet has affected the timing of conservation intervention for the remaining mainland populations of the species.”

Since 2003, the Isaac Conservation & Wildlife Trust has worked with the Department of Conservation, breeding kākāriki-rae-karaka in captivity and their captive-bred birds have been translocated to four predator-free offshore islands: Tuhua / Mayor Island (95 birds released), Te Pākeka / Maud Island (68), Oruawairua / Blumine Island (61), and Te Kākahu-oTamatea / Chalky Island (45).

So how are those birds doing now?

“In a recovery plan developed by the Department of Conservation, accurate determination of population size was listed as a key priority for the recovery and continued management of the orange-fronted parakeet. Using a mark resighting approach, Ortiz-Catedral et al. (2012) estimated that the population on Te Pākeka / Maud Island had increased from the 68 individuals released, to approximately 96–126 individuals by early 2009. Aside from this assessment, there are no published monitoring results for this population or the other populations since the initial release of orange-fronted parakeets on offshore islands.”

So a recount was definitely due – but the researchers were well aware of the challenges they faced.

Kākāriki close up on a branch
Image credit: Mark Anderson (iNaturalistNZ)

“Determining the population size of orange-fronted parakeets across their range is a difficult task. On the mainland, there are marked seasonal fluctuations in numbers linked to seed availability. Further the species is cryptically coloured and can be secretive in the wild. Finally, it can be difficult to distinguish orange-fronted parakeets from yellow-crowned parakeets unless the orange frontal band above the culmen, and the orange rump patch are clearly visible.”

So how can the total population be determined?

“In the past, a variety of approaches have been used for estimating the density of New Zealand parakeet species, including mist net catch rates, line transect surveys, five-minute bird counts, mark resighting, and fixed-point surveys. However, to compare populations of parrots across a large geographic range, a structured approach to surveying is crucial to improving the confidence with which the data can be compared and interpreted, particularly when examining multiple populations of a single species. Therefore, using a robust and repeatable method of surveying that produces precise count estimates is critical to current and future monitoring of the managed populations of orange-fronted parakeet.”

“We aimed to produce estimates of population size and density for the orange-fronted parakeets on offshore islands using a standardised fixed-point distance sampling. In our survey of Te Kākahu-o-Tamatea / Chalky Island, we also included detections of yellow crowned parakeets to understand the relative density of both parakeet species. Our research provides an update on the status of translocated populations of orange-fronted parakeet to offshore islands.”

The researchers surveyed kākāriki-rae-karaka on three of the four predator-free offshore islands that they have been translocated to.

“Our study sites consisted of three offshore island locations in the South Island of New Zealand: Te Pākeka / Maud Island, Oruawairua / Blumine Island and Te Kākahu-o-Tamatea / Chalky Island. Orange-fronted parakeets have also been released on Tuhua / Mayor Island, but we could not access this site during the timeframe of our study. We conducted our surveys at least four years after the last release of captive-bred individuals, with a mean of 6.3 years since the first release of the orange-fronted parakeets at these sites.”

The research was carried out between 2015 and 2016.

“We scheduled our surveys in this study to coincide with the nest prospecting and egg laying period to opportunistically detect nesting activities. Prior to field visits, we generated a list of 200 random points for each island, and randomly selected 50 points per island at least 300 m apart from one another (maximum distance between two points 1900 m). At each survey point, a single observer spent ten minutes sampling, attempting to detect orange-fronted parakeets and yellow-crowned parakeets (on Te Kākahu-o-Tamatea / Chalky Island). Only observers with prior orange-fronted parakeet experience participated in the surveys.”

Sampling was carried out between 7:00 am–12:30 pm each day during the peak activity period for the parakeets.

“When we detected orange-fronted parakeets or yellow-crowned parakeets during surveys, we recorded: species, size of the flock, detection type (acoustic or visual), and the perpendicular distance to the nearest metre from the initial bird location to the observer. For visual detections, we used a laser rangefinder to accurately measure the distance from the bird to the observer. Acoustic detections were noted but not included in analyses.”

“Population size was estimated for each species using the estimated density across the forested area of each island. We excluded flying parakeets from our analyses, i.e. parakeets flying above the survey point during data collection, and parakeets heard but not seen, as we cannot accurately determine perpendicular distance of these birds to the observer. Population estimates are presented as the mean density ± standard error.”

Results were mixed. Not all island translocations appear to have been successful.

On Te Kākahu-o-Tamatea / Chalky Island the researchers detected only 10 parakeets in total: five yellow-crowned, two orange-fronted and three unidentified.

“Due to a fast-approaching cold front we had to leave the island on the third field date and could not complete surveys. Due to the low number of detections of orange-fronted (2) and yellow-crowned parakeets (5), no density estimates could be obtained. The changing weather conditions forced us to reduce the number of field days at this site, but it is possible that future surveys could detect more individuals with an extended survey period.”

The results Te Pākeka / Maud Island were even more disappointing.

“We spent a total of 8.5 person-hours conducting fixed-point surveys over six days. We did not detect any orange-fronted parakeet during surveys or outside survey periods. We did not find evidence of nest prospecting or egg-laying at this locality.”

On Oruawairua / Blumine Island, however, the captive-bred, translocated birds seem to be thriving.

“We spent a total of 11.75 person-hours of fixed-point surveys over five days. We detected 20 orange-fronted parakeets visually. Based on our density estimates, the population of orange-fronted parakeets on Oruawairua / Blumine Island, is estimated at 193 ± 91 individuals. One pair of orange-fronted parakeets were observed copulating on the eastern side of the island. We did not find evidence of nest prospecting or egg-laying at this locality. We also observed a group of six orange-fronted parakeets feeding on honeydew and scale insects along the trunk of a beech tree, and a pair feeding on beech seeds along the central ridge of the island.”

So what might have gone wrong for some of the Maud Island kākāriki-rae-karaka? Back in 2009 it was estimated the population had increased from the 68 individuals released, to approximately 96–126 individuals. They seemed to be doing well.

“The absence of detections on Te Pākeka / Maud Island during our fixed-point surveys is concerning in the context of the conservation and recovery of orange-fronted parakeet. It is possible that orange-fronted parakeets are still present on Te Pākeka / Maud Island, but in very low numbers, possibly in the forest fragments excluded from this analysis.”

“Another possibility is that the herbicide treatment of the Radiata pine in the western peninsula of the island has inadvertently reduced key habitat for the orange-fronted parakeets. This area had been used from 2007 to 2009 by numerous individuals and five out of six active nests found during that period were located within the Radiata pine plantation. Although we did not access the now treated Radiata pine plantation owing to safety concerns, no activity or calls of orange-fronted parakeets from this area were detected from the paths at the edge of the plantation, which we walked for accessing survey points.”

Oruawairua / Blumine Island was the success story of the translocation survey. What makes this island different?

“Oruawairua / Blumine Island had the highest density of orange-fronted parakeets. Unlike the other islands we surveyed, Oruawairua / Blumine has a significant area of mature beech forest in the southern face of the island and large stands of regenerating forest distributed throughout the remaining habitat. Orange-fronted parakeets were observed feeding on honeydew and scale insects, a behaviour that has been observed in other native New Zealand parrot species in the mainland South Island. Honeydew is a high-carbohydrate fluid produced by scale insects as a metabolic product of their feeding on beech sap and used by many native New Zealand birds, lizards and insects as well as introduced species.”

Canopy and branches of beech
Kākāriki have been observed feeding on beech. Image credit: Jon Sullivan (iNaturalistNZ)

Could honeydew be the secret to sweet success for kākāriki-rae-karaka?

“The relationship between honeydew standing crop and population fluctuations on orange-fronted parakeets has not yet been investigated. Although orange-fronted parakeets do not feed exclusively on honeydew, this high net return resource has been linked to nest productivity in the kākā. Further, cycles of heavy beech seeding have been linked to productivity and mortality of the closely related yellow-crowned parakeets in the mainland. It is unclear to what extend the productivity of orange-fronted parakeets is linked to beech seeding and honeydew availability. Therefore, the positive relationship between orange-fronted parakeets and beech resources (honeydew and seeds) on predator-free offshore islands warrants further investigation.”

Further research might also shed a light on what happened to the Maud Island parakeet population and a recent study at Zealandia may hold some clues.

“A major concern is the apparent absence of the species from Te Pākeka / Maud Island, despite their recent successful establishment. A recent study at Zealandia (a mainland sanctuary in Wellington) of post-fledging dispersal patterns in the closely related red-fronted parakeet reports male-biased dispersal beyond the perimeter of the sanctuary, with approximately a third of study individuals effectively ‘lost’ from the Zealandia population. It is possible that post-fledging dispersal of orange-fronted parakeets from Te Pākeka / Maud Island, and limited local recruitment resulted in population decline of the species to undetectable levels. If this is the case, the possibility of releasing further captive-bred individuals on Te Pākeka / Maud Island should be evaluated, as a strategy to compensate for losses due to dispersal.”

The full research article “Estimating the population size of orange-fronted parakeets (Cyanoramphus malherbi) on offshore islands of New Zealand” was published in the NZ Journal of Zoology.