Moving to a new city can be a stressful yet exciting situation. Whether you move for a job, to learn a new language or just to get a fresh new start, you are facing a life-changing experience.
For wildlife, moving permanently from one location to another can be a life-saving experience. In many cases a change of address is usually only possible through human intervention. Conservationists have named this strategy translocation, and are currently using it for saving endangered wildlife species all over the globe.
In New Zealand, translocations are helping threatened bird species increase their populations and recover ground on their historical range. Amongst those benefited, stands the North Island kokako (Callaeas wilsoni). New Zealand’s iconic blue wattled ‘crow’ has increased its numbers almost fivefold since the 1980’s, after four decades of intensive conservation work.
Although their grayish plumage and bright blue wattles are not so easy to spot under the forest canopy, their haunting song is being heard again for the first time in many years in areas where they disappeared decades ago.
But what led to take such urgent conservation measures?
Kokako’s need for conservation action was spurred after species numbers plummeted by the end of the twentieth century. In the early 1900’s, kokako were commonly found in the forests of the North Island. But over a century’s worth of habitat destruction and the pressure of introduced predators, led to a severe decline of kokako populations.
In an effort to save remaining individuals in vulnerable native forest territories bound to be logged by local sawmills, birds were taken to pest-free nearshore islands to establish safe populations. 1981 was the start of the translocation efforts for saving the species.
Little Barrier Island and Kapiti Island, were chosen as the first sites for kokako release. Over the next decade, both islands received several translocations of birds in small numbers. Birds were still struggling in mainland populations. Ship rat and stoat predation on eggs, chicks and adult females limited kokako’s breeding success in unmanaged sites.
In the mid 90’s, kokako were released in two new sites, Trounson Kauri Park and Pikiariki Ecological Area, Pureroa. As in the previous releases, birds were fitted with radio transmitters to monitor the birds’ survival. Post-release monitoring is crucial to understanding what influences kokako establishment success, but in some instances transmitters fail. After a few months of being released, some of the birds from both sites disappeared, never to be seen again. These were cataloged as failures and no further attempts were made there.
By 1999, the numbers looked grim. Only 330 pairs remained in 13 populations in the mainland, with an additional 70 pairs of translocated birds in Little Barrier Island and Kapiti Island.
The Department of Conservation was working harder than ever. The Kokako Recovery Group was formed and the North Island kokako Recovery Plan was updated to set new research and management priorities for the project.
Before the turn of the century, Tiritiri Matangi Island and the Hunua Ranges became new release sites. Tiritiri Matangi Island was chosen with the intention of preserving the last individuals from Taranaki. Kokako were to be returned to Taranaki only after conditioning a pest-managed area. Now after 18 years of their absence, kokako have finally returned to the Parininihi Forest in North Taranaki in 2017.
In spite of the success with using Tiritiri Matangi for establishing new populations, kokako potentially require genetic management for their population. Due to the island’s small area (196 ha), kokako face the risk of inbreeding depression .
Usual genetic management efforts include taking individuals from one location to another, to increase genetic diversity. But catching adult kokako can be quite difficult and expensive. There is a risk of transferring diseases and parasites from other areas and adult kokako from different locations don’t speak the same dialect!
So, in an attempt to avoid all of these issues and try new methods, a swap of eggs between Tiritiri Matangi and Hunua Ranges occurred in 2010. Three eggs were exchanged from nests between the Hunua Ranges and Tiritiri Matangi I. This attempt turned out to be unsuccessful. Nevertheless, kokako in Tiritiri Matangi Island prevailed under current management, and their presence is gaining advocacy benefits for the species thanks to plenty of encounters that visitors have with the local population.
For the Hunua Ranges, the story was quite different. Kokako were moderately abundant before releases, but translocation of new individuals posed the possibility of speeding up population recovery. After four releases kokako established themselves, making it the only successfully supplemented population to date.
Subsequent translocations to mainland islands in the early 2000’s proved to be successful. Boundary Stream, Pukaha (Mt Bruce), and Ngapukeariki shared common features, they all received over 15 birds (which was proving to be an adequate release number), and they all had an effective control of key pests.
With these releases, new management methods were put on trial and in 2006 post- translocation monitoring, by Laura Molles and colleagues, involved acoustic anchoring. Playback of kokako song was broadcasted in released areas to maximize the chances of kokako staying in the target zone.
Ngapukeariki, the Hunua Ranges and Whirinaki became the first sites to use this method as an attractant for the reintroduction of a terrestrial bird. All sites received different responses from the translocated birds but, overall, kokako seem to find speakers attractive and the method showed potentialgiven its low risk and inexpensive nature.
By 2010 kokako were already showing a positive response from the previous years of conservation efforts. The numbers from 1999 almost doubled to 780 pairs in 21 populations (10 newly established populations and 1 supplemented). Kokako’s conservation status was upgraded from “threatened” to “at risk-recovering” in 2019.
Numbers are reported to be around 1,600 pairs from the latest officials DOC reports. But kokako specialist Dave Bryden estimates the current populations may be around 1,900 pairs. Currentl.y the Kokako Specialist Group (former Kokako Recovery Group) is working towards continuing new translocations in the next year for Mt Pirongia, Parahinini Forest and Waitakere.
As the 40th anniversary of the first kokako translocation approaches, we recognize translocations and management of key pests as effective strategies for the recovery of threatened bird populations. Thanks to the hard work of the Kokako Specialist Group, the Department of Conservation and numerous enthusiastic volunteers kokako sightings are becoming ever more frequent beyond those on our 50 dollar bill.
The author Mariana Aguas Hernandez is a postgraduate student in the Master of International Nature Conservation taught jointly at Lincoln University and University of Göttingen. She wrote this article as part of her assessment for ECOL 608 Research Methods in Ecology.
Source: Innes, J., Molles, L.E., Speed, H. (2013). Translocations of North Island kokako, 1981-2011. Notornis 60(1):107-114