Sand martins, house martins and swallows all migrate across the Sahara Desert to reach Europe. This is an arduous journey because there is little or no food on the way. Martins and swallows have to stop regularly during the journey, to rest their wings. Some birds become exhausted and die where they land. Oases are invaluable stop-off points. Warblers, flycatchers, redstarts, wagtails and other small birds can feed and rest at an oasis. Wading birds can find no food in the desert, so won't get a meal until they arrive at the coastal mudflats. When they arrive at the African coastal lagoons they stay several days, feeding continuously. Curlew sandpipers and spoonbills feed in the shallows.