Asia’s rarest seabird could be easier to spot in the future
Researchers celebrate breeding success in South Korea for the Chinese Crested Tern – a bird once thought extinct. Decoy model birds have helped bolster the new colony, and the species has been spotted in Japan for the first time.
Trying to spot a Chinese Crested Tern amongst a colony of similar-looking Greater Crested can be likened to playing a high-pressure game of ‘Where’s Wally?’, in which rather than simply completing a fun puzzle-book by spotting a man in a red-striped jumper, the fate of an entire species relies on your attentive eyes.
So when, about three years ago, we reported a momentous discovery in the conservation of Asia’s rarest seabird, the Chinese Crested Tern Thalasseus bernsteini, we were very excited by what it could mean. Korean researchers had spotted five adults and one chick amidst a colony of Black-tailed Gulls on an uninhabited rocky island (Chilsando), 7 km off the southwest coast of South Korea. This was extra special because Chinese Crested Tern was feared extinct until 2000 when breeding birds were rediscovered on the Matsu Islands of Chinese Taiwan, and hadn’t been seen on the eastern side of the Yellow Sea for almost 100 years. Yunkyoung Lee, Researcher from the National Institute of Ecology (South Korea), remembers the moment well:
“When I realised that we were looking at Chinese Crested Terns, I felt a thrill throughout my whole body”, she says. “Their slender appearance with black caps and white backs was eye-catching in the crowded colony of Black-tailed Gulls Larus crassirostris, which have white rounded heads and grey backs. However, in the field, we did not know immediately what they were. We had never seen this species before, let alone ever anticipated that they would lay eggs in Korea.”
Taking quick action, Lee and her team immediately ensured the Critically Endangered terns’ safety by restricting access to the area. At the time the species’ entire global population was thought to be less than 100 individual birds.
As well as the importance of the location, the fact the birds were nesting amongst gulls was special, because previously Chinese Crested Terns found nesting well on the west of the Yellow Sea since 2000 were amongst colonies of Greater Crested Terns Thalasseus bergii, the slightly larger, much more common cousins of the Chinese Crested. The Greater Crested aren’t found as far north as the Korean peninsula, and Chinese Crested’s range was further north historically, so it was assumed they’d adapted their range in order to find a way to breed in a colony.
You see it’s tough being naturally sociable when there’s no-one left to hang around with. The Chinese Crested Tern is a very gregarious species, relying on the presence of a large colony to feel comfortable enough to breed successfully. Late-breeders will even desert their nests if the colony starts to disperse, according to close observation by BirdLife’s Simba Chan, Senior Conservation Officer of BirdLife Asia Division and National Geographic Explorer, when he dedicated two breeding seasons in 2014 and 2015 carefully camped out (relying on shipment of food and water, and braving a typhoon) on the Jiushan Islands (off the coast of Zhejiang, southeast China [see map below]) in order to protect newly-found Chinese Crested Terns there (amongst Greater Crested) from disturbance. The 2016 discovery in South Korea also indicates that Chinese Crested Terns there are breeding earlier than normal in order to match the breeding times of the Black-tailed Gulls.
The key, therefore, to the conservation of Chinese Crested Terns is increasing nesting success by making the birds feel safe. This is achieved through preventing disturbance and by using social attraction techniques, such as using model decoy birds and call-playback systems to bolster the colony. Almost three years later, this kind of direct conservation effort is paying off in South Korea: this breeding season seven Chinese Crested Terns were monitored at the South Korean island, with at least one chick fledged.
Social attraction techniques were developed by Dr. Stephen Kress (Vice President for Bird Conservation, National Audubon Society [BirdLife USA]) for the restoration of Puffin colonies in the USA in 1970s, and has proven to be effective in restoring colonial seabird breeding sites. Since 2013, the adaptation of these techniques by Chan and colleagues has successfully restored the deserted Chinese Crested Tern breeding colony of the Jiushan Islands, leading to a record-breaking number of Chinese Crested Terns being found there (over 50!) during Chan’s protective stake-out seasons, doubling the known population at the time. This shows that the islands along the eastern China coast were highly disturbed (and perhaps even exploited) and so the terns congregated on the one island that had been made safe. Chan then recommended the use of social attraction to help the South Korean birds.
“I am pleased that social attraction methods have helped Chinese Crested Terns establish new colonies” said Dr. Kress. “This is good news for the species. Multiple nesting colonies within an expanded range reduces the risk of having most of the population in one location. Because each site brings its own risk to the species, multiple sites help to assure that some of the population will survive regardless of what happens at other colonies.”
"Exploitation and disturbance by humans are the main reasons for the failure of breeding," says Chan, "and I believe pollution is the main reason for embryos dying before hatching.” But there’s hope: “Unlike the southern breeding grounds, the coast of southwestern Korea is safe from human disturbance because the site is well-guarded. The pollution level is much lower too so it’s an ideal place for Chinese Crested Terns. Other potential risks, such as typhoons and hybridisation with Greater Crested Terns, will also be negligible at the site in Korea.”
The migration route of this mysterious bird still remains undiscovered, but the rediscovery of up to three Chinese Crested Terns at Panabo, Mindanao of the Philippines from 10 till 13 March 2018 has given tantalizing clues.
Plus if that wasn’t good news enough, Chinese Crested Tern have now also been spotted for the first time in Japan. On 20 October 2018, Dr Vladimir Dinets, a biologist teaching in Okinawa, took photos of Chinese Crested Tern while driving on the bridge linking the islands of Miyako and Irabu. “Given the vicinity of Japan to the Chinese Crested Tern’s current range, this discovery is long anticipated,” commented Chan. “But that doesn’t make it any less exciting! Also, the date of discovery might suggest that the post-breeding wandering stage of this species is quite long, meaning the potential success of using social attraction at new breeding sites is higher than previously expected.” If our work successfully continues, it looks like the puzzle of Where’s Wally for Asia’s rarest seabird could hopefully get a lot easier in the future.
The BirdLife International Chinese Crested Tern project is generously funded by the Ocean Park Conservation Foundation, Hong Kong; the Tilia Fund; the BirdLife Preventing Extinctions Programme; the National Geographic Society; and the Honk Kong Bird Watching Society (BirdLife in Hong Kong, China).
Thanks to Yu Yat-tung of the Hong Kong Bird Watching Society, Dr Park Jin-young and National Institute of Biodiversity Research of Korea, Dr Lee Kisup of Waterbird Network Korea for supporting and giving advice to the project, and Dr Kiyoaki Ozaki of Yamashina Institute for Ornithology in Japan for the discovery of Chinese Crested Tern in Japan.