The red knot is a migratory shorebird that travels up to 20,000 km twice a year from its breeding grounds on the high Arctic tundra to its southern non-breeding sites. Along with having one of the longest total migrations of any bird, some populations also fly as much as 8,000–9,000 km between stopover sites in a single flight. As a shellfish-eating specialist avoiding pathogen-rich freshwater habitats, the red knot relies on the few large tidal flats with abundant food resources that the world has to offer. To undertake the physiologically demanding flight from West Africa to northern Siberia, for example, Calidris c. canutus refuels during three weeks of fast feeding in the national parks of Banc d’Arguin in Mauritania and the European Wadden Sea. After nearly doubling its weight, it burns off stored fat during the 3 or more days of non-stop flying.