Princeton University researchers may have solved a long-standing mystery in conservation that could influence how natural lands are designated for the preservation of endangered species.
Around the world, the migratory shorebirds that are a conspicuous feature of coastal habitats are losing access to the tidal flats — the areas between dry land and the sea — they rely on for food as they travel and prepare to breed. But a major puzzle has been that species’ populations are plummeting several times faster than the rate at which coastal ecosystems are lost to development.
Nowhere is the loss of tidal flats and shorebird species more acute than along the East Asia-Australasian Flyway (EAAF). An estimated 5 million migratory birds from 55 species use the flyway to travel from southern Australia to northern Siberia along the rapidly developing coast of China — where tidal flats can be more than 6 miles wide — at which birds stop to rest and refuel.
Mu studied birds at two well-known stopover sites in the Yellow Sea region, Nanpu (b) near Beijing and Rudong (c) outside of Shanghai. The dark squares indicate the study plots along the upper, middle and lower tidal flats (dotted area). In Nanpu, the flats span north to south, and run south to north in Rudong. The white areas represent the sea beyond the low-tide line.
Since the 1980s, the loss of tidal flats around the Yellow Sea has averaged 1.2% per year. Yet, the annual loss of the most endangered bird species has averaged between 5.1 and 7.5%, with populations of species such as the critically endangered spoon-billed sandpipers (Calidris pygmaea) climbing as high as 26% each year.
In exploring this disparity, Princeton researchers Tong Mu and David Wilcove found a possible answer — the birds don’t use all parts of the tidal flat equally. They discovered that migratory shorebirds overwhelmingly rely on the upper tidal flats closest to dry land, which are the exact locations most often lost to development.