February
5, 2016
The
shrinking of mudflats along the coasts of the Chinese Yellow Sea is an
increasing problem for migratory birds that travel between Siberia and
Australia. Research by an international team of ecologists, led by Spinoza
laureate professor Theunis Piersma, a senior scientist at NIOZ Royal
Netherlands Institute for Sea Research and professor in Global Flyway Ecology
at the University of Groningen, 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 increasing claim of land by the Chinese
government.
The
research, published in the Journal of Applied Ecology, involves three
migratory bird 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 of these species winter
in Roebuck Bay, Western Australia. On their way between Asia and Australia they
roost and refuel along the coasts of the Yellow Sea.
The
cause
Thanks
to thousands of color ringed birds, and more than thirty thousand resightings
of these birds, the ecologists were able to calculate the annual, as well as
the seasonal survival of the three species between 2006 and 2013. The
production of eggs and fledglings was no issue in that period. Also, the
survival in their Australian wintering grounds was normal. However, from 2010
onwards, the survival showed a sharp decline in a period that included the
spring and fall migration, as well as 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 along the Yellow Sea,
where significant loss of habitat was going on because of land claim by the
Chinese government.
Populations
in decline
Previous
research by the group of Piersma has shown that the survival of birds like the
knot and the godwit is normally evenly spread across the year. Until 2010 this
was also true for the knots and the godwits that roost along the shores of the
Yellow Sea. The populations were stable. With the decline in survival in 2011
and 2012, however, the populations began to shrink. 'Should the survival
continue to shrink like it did in these years, we'll see a decline in these
populations to half within three or four years', Piersma predicts.
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