If you are lucky to see the Critically Endangered Spoon-billed Sandpipers or Endangered Nordmann’s Greenshanks on the southern Jiangsu coast, they are probably busy gobbling up seafood on the vast tidal flat.
In the past decade, people have come to realize that the southern Jiangsu coast of China is an important staging site for the two species. They come here to rest and refuel in spring and autumn, until they’ve gained enough sustenance and strength to embark on the next leg(s) of their arduous migration journey.
People did not notice what the two species do here in Jiangsu other than fattening up ahead of the next journey. A recent study published in Bird Conservation International shed new light on their stopover ecology.
By analyzing the two species’ primary moult schedule, the article gave a new perspective on the importance of southern Jiangsu coast to Spoon-billed Sandpipers and Nordmann’s Greenshanks.
The ‘untold secrets’ of Spoon-billed Sandpipers and Nordmann’s Greenshanks
In 2015, the research team led by Spoon-billed Sandpiper in China (hereafter SBSinChina) conducted a study on the southern Jiangsu coast. From July to November, the team carried out 21 surveys to record the number and moult schedule of adult Spoon-billed Sandpipers and Nordmann’s Greenshanks at Tiaozini, Xiaoyangkou and Dongling.
Their results showed that during southward migration, Spoon-billed Sandpipers started arriving on the Jiangsu coast on August 19 and stayed for 66 days on average. During their stay here, over 85% of the adults were replacing their primary feathers. According to the modelling analysis, primary moult in Spoon-billed Sandpipers started on August 08 and lasted for around 73 days.
In contrast, 91% of the adult Nordmann’s Greenshanks replaced their primary feathers on the southern Jiangsu coast, and their average moult duration was 65 days. Compared to Spoon-billed Sandpipers, Nordmann’s Greenshanks spent a longer time (84 days on average) in Jiangsu, and their stopover dates almost completely overlapped with their moult schedule. These are life history data unknown before.
So, what does it mean for birds to moult their primary feathers on the southern Jiangsu coast?
The ‘dressing room’ on the Jiangsu coast
Although feathers evolved in the early ancestors of birds some 200 million years ago, feather is a unique characteristic of modern birds.
Feathers serve a variety of functions including thermoregulation, courtship display, camouflage and especially flight. Every year, feathers become worn or damaged due to flight, sun exposure and sometimes parasites, so birds must replace their feathers on a regular basis.
Moult is an energetically costly process, and this is especially true if birds replace their long primary flight feathers. This explains why few birds overlap primary moult with other important life-history processes such as breeding and long-distance migration.
When birds moult their primary feathers, they also become more vulnerable. They need abundant food supplies and safe shelters to complete the process. The survey results indicate that the southern Jiangsu coast serves as a ‘dressing room’ for Spoon-billed Sandpipers and Nordmann’s Greenshanks, meaning this region has the necessary resources to support the primary moult process.
There aren’t that many ‘dressing rooms’!
It’s clear from the study that the southern Jiangsu coast is more than just a shorebird ‘restaurant’. Besides the DPRK, there’s no other reliable record of moulting site for Spoon-billed Sandpiper and Nordmann’s Greenshank. Therefore, the authors are confident to say that the southern Jiangsu coast is the major moulting ground for the two endangered species.
In addition to the two species, the SBSinChina team noticed that Great Knots, Bar-tailed Godwits, Greater Sandplovers and Eurasian Curlews were also moulting their primary feathers. This reinforces that the southern Jiangsu coast is indispensable for migratory shorebirds.
What’s worth noting is that, although we use the word ‘dress’ as a metaphor for feathers, primary feather moult is much more important than changing clothes. We human cannot stay warm without dresses, but birds can barely move without primary feathers!
Current situation and future perspective
Currently, tidal flats along the southern Jiangsu coast still face multiple threats including invasion of spartina grass and loss of high-tide roosts. In the past few decades, shorebirds that are highly reliant on the Yellow Sea for stopover experienced a sharp decline in their population.
As Tiaozini became part of the natural World Heritage Site in 2019, Xiaoyangkou and Dongling may also be included on the tentative list for phase II of the serial nomination. We hope that one day, Spoon-billed Sandpipers and Nordmann’s Greenshanks are no longer endangered, so that people can always sneak a peak at them ‘getting dressed’!
Article available [here], doi:10.1017/S0959270920000210
Prepared by Yang Ziyou from Spoon-billed Sandpiper in China.