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Egg Swap for Operatic New Zealand Birds a Success, but Invasive Predators Create Discord

The views expressed are those of the author and are not necessarily those of Scientific American.


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kokakoNew Zealand used to be home to two subspecies of the rare birds known as kōkako (Callaeas cinereus). Today only one subspecies remains. The South Island kōkako was last seen in 1967 and was finally declared extinct six years ago. Conservationists are determined to save the remaining subspecies, which can still be found in the forests on New Zealand’s North Island, from the same fate. Unfortunately with fewer than 800 breeding kōkako pairs and a total population of maybe 1,500 birds—all of which are scattered in small population segments—maintaining a healthy population in the wild remains a challenge.

To help improve the genetic diversity of endangered kōkako, which are known for their long, piercingly beautiful songs, the New Zealand Department of Conservation (DOC) and its partners turned to a method previously used with California condors. Last year biodiversity rangers found mother kōkako birds nesting on Hunua and Tiritiri Matangi Islands. The humans climbed into the nests, carefully removed five fertile eggs and switched them into nests on the other islands, an action designed to keep the gene pool flowing between the two locations. The mother birds never seemed to notice the sleight of hand and incubated the transferred eggs, three of which hatched. The mothers then reared the chicks as if they were their own. While three chicks from five eggs may not seem like a success, it is actually a very good rate for the birds, which all too often lose their eggs or chicks to predators during their long, 50-day nesting period.

According to the DOC, the wild-to-wild egg transfer contributed to a very successful 2012-2013 breeding season, which has increased the number of breeding birds by 20 percent. The DOC and its partners have also worked to control invasive predators such as possums, rats and stoats on the two islands.

Unfortunately predators still plague the birds in other locations. The day after the DOC announced the breeding success they delivered bad news: the 27 kōkako released on Secretary Island in 2008 and 2009 as well as a juvenile born on the island in 2011 have all disappeared. The birds were radio-monitored for nine months after their release until the batteries on the devices ran out. A field survey last month failed to find them. “At this stage we cannot categorically say there are no surviving kōkako on Secretary Island,” DOC ranger Megan Willans said in a press release. “However evidence suggests that sadly most of the birds have perished.”

The DOC theorizes that stoats, a type of weasel, may have made the 1-kilometer swim from the mainland onto the island. They don’t have direct evidence of that migration, but they did confirm that the predator population on the 81-square-kilometer island has spiked. In addition to the stoats, one kōkako was killed by a falcon shortly after it was released onto the island. The DOC will now analyze and research the threats before attempting to translocate any additional birds to Secretary Island.

Kōkako are one of just two remaining members of the family Callaeidae, the other being the previously endangered saddleback, or tieke (Philesturnus carunculatus), which has bounced back following decades of intense conservation efforts. The DOC learned a lot from its efforts to boost tieke populations. Let’s hope the kōkako will one day enjoy the same success.

Photo by David Cook, used under Creative Commons license

Previously in Extinction Countdown:

John R. Platt About the Author: Twice a week, John Platt shines a light on endangered species from all over the globe, exploring not just why they are dying out but also what's being done to rescue them from oblivion. Follow on Twitter @johnrplatt.

The views expressed are those of the author and are not necessarily those of Scientific American.





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