A new report reveals a drastic population decline in the Red Knot subspecies Calidris canutus rufa with surveys showing that numbers at its wintering grounds in southern South America have fallen drastically in recent years.
The 2007 Red Knot Assessment Report, prepared by the US Fish and Wildlife Service, reveals that the rufa subspecies could become extinct within ten years, if adult survival remains low. The numbers in its wintering area have gone from 51,300 in 2000 to approximately 30,000 in 2004, and now still further to just 17,200 in 2006.
Although the causes of the population crash are not yet fully understood, the dramatic decline is mainly attributed to the low availability of horseshoe crab eggs in Delaware Bay, USA, a key stopover site for Red Knot Calidris canutus rufa. Exploitation by the conch and eel fishing industries is a likely cause of the lack of eggs thanks to an elevated harvest of adult crabs for bait. Even if this exploitation ceases immediately, scientists predict it would take years before the horseshoe crab population recovers to its former level.
Of the six Calidris canutus subspecies, rufa travels the longest distance, between breeding areas in the Canadian Artic and wintering areas in Patagonia and Tierra del Fuego.
Recent unexplained Red Knot die-offs have highlighted further the need for research into the variety of threats afflicting the already declining rufa population. In April, more than 1300 dead Red Knot were discovered at two sites in northern Uruguay. Aves Uruguay, in connection with other national and international organisations, is already working in the area to establish the possible causes of the casualties and the role of Uruguay as stopover for the species.
“The death of more than 1,300 Red Knots in Uruguay is of particular concern given the low overall population size,” said Rob Clay, Conservation Manager of BirdLife’s Americas Secretariat. “This number represents over 6% of the [rufa] population, all of which winter in southern South America. The discovery underlines the need to better understand factors which may be affecting the species during migration and on its wintering grounds.”
See Red Knot report here.
Source: BirdLife International