Lagoa do Peixe is forty kilometres of brackish water on the southern coast of Brazil, in Rio Grande do Sul between the Atlantic and the huge Lagoa dos Patos, and it is never deeper than your shins. The shallowness is the point. It lays bare kilometre after kilometre of mudflat full of the small invertebrates migrating birds eat. Up to a fifth of the world's rufa red knots come down on these flats, with nineteen other Arctic shorebird species, in the austral spring and again in autumn, breaking the journey between the Arctic and Tierra del Fuego. One red knot tracked from here flew about 8,300 kilometres without landing. At the water's edge they feed in restless flocks, red knots with sandpipers and Hudsonian godwits, probing the mud and fattening for the next leg. Given long enough you can pick out the rust-coloured breeding plumage the knots will carry north.
Further out, Chilean flamingos work the same shallows with their heads down, sifting, and in low morning light their loose pink ranks stand clear against the grey. They are not passing through. The flamingos winter here, a few hundred of them now where older records describe great flocks. Behind the beach the dune belt holds its own residents. Burrowing owls stand sentry at the mouths of their sand holes, and the tuco-tuco, a stout burrowing rodent named for the tuc-tuc it drums out from underground, has its entire world range in this narrow strip of coast. On the ocean side the beach runs north for kilometres with surf on one side of you and the flats on the other, and you leave barely a footprint before the lighthouse. None of this runs by itself. A sandbar shuts the lagoon off from the sea for most of the year. When the autumn winds pile the water up, the channel is cut open, tractors and all, to let the ocean back in. The timing of that cut, balanced against the flooded pastures inland, is what bares the mud the hemisphere's birds come down onto.