Dr Nial Moores, Birds Korea
An article published in Nature Communications on 13th April this year deserves very wide reading and frequent citation. Entitled, “Rapid population decline in migratory shorebirds relying on Yellow Sea tidal mudflats as stopover sites” the multi-author account presents compelling evidence on declines in migratory shorebirds – linking these declines in birds counted during the boreal winter in Australia and New Zealand to the level of each species’ dependence on the Yellow Sea during migration.
The research shows that species, and even in one case a subspecies, which are most dependent on the Yellow Sea have declined at greater rates than those which are less dependent on the same sites. For example, menzbieri Bar-tailed Godwit, which are fully dependent on the Yellow Sea during both northward and southward migration, have declined more rapidly than baueri Bar-tailed Godwit, which only depend on the Yellow Sea during northward migration.
The authors, many with names that will already be familiar to Birds Koreans (either as participants of the 2006-2008 SSMP or as authors of other important papers) add that available evidence implies that “population declines are driven by low survival during or soon after staging in Yellow Sea tidal mudflats, likely because birds are unable to refuel enough to meet the energetic demands of migration”. They also identify two sources of long-term environmental decline in the Yellow Sea as “likely responsible for the negative impacts on migratory shorebird populations. First, nearly 30% of Yellow Sea tidal mudflats were lost to coastal development in the past 30 years, a period that brackets the timing of observed population declines. Coastal China is forecast to undergo up to 14% expansion in urban development over the next 15 years, much of it concentrated on the margins of the Yellow Sea, and tidal mudflat loss seems likely to continue or accelerate. Second, the Yellow Sea ecosystem has undergone pervasive degradation in quality, including massive algal blooms, discharge of heavy metals and pesticides; and the spread of the exotic saltmarsh-grass Spartina alterniflora. These disturbances reduce prey availability and foraging opportunities for migrating shorebirds.”
The full abstract and a link to the full article by Colin Studd et al are below:
Migratory animals are threatened by human-induced global change. However, little is known about how stopover habitat, essential for refuelling during migration, affects the population dynamics of migratory species. Using 20 years of continent-wide citizen science data, we assess population trends of ten shorebird taxa that refuel on Yellow Sea tidal mudflats, a threatened ecosystem that has shrunk by 65% in recent decades. Seven of the taxa declined at rates of up to 8% per year. Taxa with the greatest reliance on the Yellow Sea as a stopover site showed the greatest declines, whereas those that stop primarily in other regions had slowly declining or stable populations. Decline rate was unaffected by shared evolutionary history among taxa and was not predicted by migration distance, breeding range size, non-breeding location, generation time or body size. These results suggest that changes in stopover habitat can severely limit migratory populations.
ARTICLE Rapid population decline in migratory shorebirds relying on Yellow Sea tidal mudflats as stopover sites.