The Yellow Sea – a rapidly narrowing bottleneck for migrating shorebirds

The shrinking of mudflats along the coasts of the Chinese Yellow Sea is an increasing problem for birds trying to migrate between Siberia (for breeding) and Australia and New Zealand (for survival when not breeding). Research by an international team of ecologists from The Netherlands, Australia and China, led by the Chair in Global Flyway Ecology at the University of Groningen and staff member of Royal NIOZ, Theunis Piersma shows that three different species are in decline because of one common factor: loss of food and habitat along the coasts of the Yellow Sea, because of the still increasing losses of the fertile shallow foreshores, especially in China.

The research, now published in the Journal of Applied Ecology, involves three migratory shorebird species. The red knot (Calidris canutus piersmai) breeds on islands north of eastern Siberia. The great knot (Calidris tenuirostris) breeds in the alpine areas of north-eastern Siberia, and the bar-tailed godwit (Limosa lapponica menzbieri) breeds in the lower wetlands of north-eastern Siberia. All three species spend the nonbreeding season on the intertidal foreshores of tropical north-west Australia. On their way between Australia and Asia they roost and refuel along the fertile foreshores of the Yellow Sea.

The foreshores of the Yellow Sea
The foreshores of the Yellow Sea are extensive and fertile, providing rich feeding grounds for both humans and shorebirds. Nanpu mudflats, Luannan, China, May 2013. Photo by Ying-Chi Chan.

Thanks to the colour-ringing of thousands of individual shorebirds, and the more than thirty thousand subsequent resightings, we were able to calculate the annual, as well as the seasonal survival of the three species between 2006 and 2014. From 2010, the survival showed a sharp decline during a period that included the spring and autumn migration and the breeding period. Because the snow melted relatively early on the breeding grounds in those years, there was no reason to believe that the survival was any different during that period. That left only one culprit: the conditions during migration at the East Asian staging grounds, where significant loss of habitat is ongoing because large areas of the shallow seas around the Yellow Sea are turned into land, particularly in China.

Enormous areas of high quality intertidal mudflats
Enormous areas of high quality intertidal mudflats must have been lost recently during land claims like the present near Rudong, Jiangsu province, China. On the basis of satellite telemetry data we know that the pictured areas were used by staging bar-tailed godwits until a few years ago. Photo taken in October 2015 by Theunis Piersma.

Our research along shorebird flyways in Europe and Africa had shown that survival is normally evenly spread across the year. Until 2010 this was also true for the two knot species and the bar-tailed godwits using the shores of the Yellow Sea during both northward and southward migration; the populations remained stable during these years. With the decline in summer survival in 2011 and 2012, the populations began to shrink. If the low summer survival is upheld, we’ll see a decline in these populations to half of their present size within three or four years.

flock of red knots
Coauthor Matt Slaymaker taking a break from scanning a flock of red knots at the Nanpu coast, Luannan, China (May 2014) for individual colour-ring combinations. On the basis of such resighting work, carried out systematically throughout the year in both northwest Australia and China, and using novel demographic approaches, we were able to calculate time-trends in seasonal survival. Photo by Ying-Chi Chan.

Unless there is solid scientific evidence for negative effects on the environment, governments tend to err in favour of supposedly (and usually rather short-term) economic benefits rather than putting a halt to activities that harm issues including nature and biodiversity. but in the present case also including human health, sustainable fisheries and coastal protection. With this research, mainly funded from Europe by Birdlife Netherlands and WWF Netherlands, we delivered further proof that land claims around the Yellow Sea put many migratory birds at serious risk.

Bar-tailed godwits under assault
Bar-tailed godwits under assault. The plight of migrating shorebirds as a consequence of rapid shoreline habitat loss in the Yellow Sea is well illustrated by these staging Bar-tailed Godwits roosting on an active dredge-dumping site on 20 April 2012. The material was being excavated from a channel to improve access to the Donggang Fishing Port, Liaoning Province. The infilled area is planned to be part of an industrial park to be built on an area of intertidal mudflat that was excised from the Yalujiang National Nature Reserve by a boundary adjustment in 2012. Photo by David S. Melville.

About the author:

Founder of the applied research consortium Global Flyway Network, Theunis Piersma tries to shape the best possible ecological research on migrant birds in wetland habitats. A contributor to over 400 scientific publications, together with his research teams at NIOZ and RUG and within strong international collaborations, his research is strongly focused on the individual animal, with much consideration for the environmental context in which they have to make their foraging and movement decisions. Together with Jan van Gils he wrote the enthusiastically received ‘The flexible phenotype. A body-centred integration of ecology, physiology, and behaviour’ (Oxford University Press, 2011). In April, BTO will publish his ‘Guests of summer. A House Martin love story’ (with a foreword by Ian Newton). In 2014 he received the prestigious Spinoza Premium, the highest accolade for working scientists in The Netherlands.

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