Coastal wetlands serve as critical habitat to many bird and fish species, as well as barriers to coastal erosion and sinks for a variety of pollutants.

Rising sea levels will affect wetlands, barrier islands and other coastal habitats by inundation of marshes or mudflats, saltwater intrusion, and erosion.

From the sight of thousands of shorebirds wheeling in perfectly synchronized flight over a marsh, to the soft calling of millions of song-birds as they fly overhead on an autumn night, or the ghostly silhouettes of geese seen passing across a full moon, t here are few natural spectacles on Earth that match the mass migration of birds.

Not all birds migrate, but those that do perform incredible feats of physical endurance and global navigation. The aim of most migratory birds is to find safe nesting sites and the best source of food for the summer breeding season, and then to return to a warmer, more hospitable habitat to over-winter. Most birds make their first migration, often thousands of miles long, just weeks after they have hatched. The mystery of how birds find their way to ancestral wintering spots halfway across the globe and b ack again, has still not been fully solved by scientists. Birds appear to use many clues to navigate, including the sun, the stars, and an internal biological magnetic compass.

They also follow visual cues such as coastlines and rivers. No matter how they find their way, the distances they fly in doing so can be truly phenomenal.

No creature on earth migrates farther than the beautiful Arctic Tern, which can cover more than 30,000 km (18,000 miles), in its journey from Arctic Canada or Siberia to the South Pole and back again. This silvery-white, sliver of a bird weighs less than half a pound, and yet can virtually circumnavigate the globe in the course of a year's seasons.