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Contributing factors sought as Red Knot population plummets

Wintering population in drastic decline

A new report has revealed a drastic population decline in the Red Knot subspecies Calidris canutus rufa. Numbers at their wintering grounds in southern South America have fallen drastically in recent years; from 51,300 in 2000 to approximately 30,000 in 2004, and still further to just 17,200 in 2006.

The 2007 Red Knot Assessment Report, prepared by the US Fish and Wildlife Service and based on demographic studies covering 1994-2002, reveals that the rufa subspecies could become extinct within ten years, if adult survival remains low.As result of the significant declines, Red Knot Calidris canutus rufa has been included under Appendix I of the Convention of Migratory Species by request of the Argentinean government. In Canada, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has listed it as Endangered.

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.

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. The lack of eggs has been attributed to an elevated harvest of adult crabs for bait in the conch and eel fishing industries. Studies show that Red Knot individuals with lower body weight at departure in Delaware Bay have lower survival than heavier birds.

Even if crab exploitation ceases immediately, scientist predict it would take years before the horseshoe crab population recovers to its former level. Other possible contributing factors in the decline include the loss of critical habitats, contamination and the spread of non-controlled tourism activities at their wintering and migration areas.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, 312 dead Red Knot Calidris canutus rufa were discovered by a park guard at Playa La Coronilla in northern Uruguay and the same day over 1,000 birds were found dead at a second site nearby. Of the events Joaquín Aldabe, IBA coordinator at Aves Uruguay (BirdLife in Uruguay) commented: It seems possible that harmful algal blooms could be related to it, although additional studies are required in order to fully understand this unexpected event. 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 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.The Western Hemisphere Shorebird Reserve Network (WHSRN), a partnership of organisations working to conserve shorebirds and their habitats through a network of key sites across the Americas, will soon release a Species Conservation Action Plan for the Red Knot in the Western Hemisphere.

is the work of the Red Knot Species Assessment Team, comprising dozens of expert authors across the hemisphere. Charles Duncan, Director of the Executive Office of WHSRN said: We are committed to working collaboratively with partners, like BirdLife’s network of affiliates, at the enormous geographic scale needed to ensure not only the survival, but the recovery of healthy populations, of Red Knots and other shorebirds in the Americas. This will require targeted conservation action, scientific understanding of the causes of the declines, and monitoring of threats and population levels.

utive Office of WHSRN is a key program of the Manomet Center for Conservation Sciences, in Manomet, Massachusetts, USA.

4th July 2014