The eggs of the horseshoe Crab are the main food source for many migratory shorebirds, such as the sanderling that stop over in Delaware Bay to refuel.

Climate change will disrupt the seasonal timing of annual migrations and available food sources.

Wetlands have high biological diversity and are refuges and breeding grounds for many species, but most notably birds.

Climate change will alter wetlands primarily by changing the hydrology that sustains them.

Bird migration superbly demonstrates the complexity and the wonder of the web of life. The evolution of individual migratory strategies of different bird species over the past tens of thousands of years represents a delicate balance of nature, making it very sensitive to the impacts of human activity. One such human influence, global warming (caused mainly by the burning of coal and oil since the Industrial Revolution), threatens to cause catastrophic alteration to this delicate balance.

For most migratory birds, the weather and the availability of food along the migratory route, are two critical factors for the success of their long and arduous journey. Global warming is already changing both these factors. Long-distance migrants may be in the air for many hours at a time, and travel hundreds or even thousands of miles without stopping. These kinds of flights are only possible if the birds can feed adequately before setting off, to store enough energy for each stage of the journey. Birds feed feverishly before migration and may double their body weight, building up fat reserves to keep them going for the long flight ahead.

If birds don't have access to food sources at staging points along their routes, they are not able to complete their migrations. Some coastal sites, such as the Chesapeake Bay in the US, and Mai Po Marshes in Hong Kong, are such important refueling stops for migratory bird species, that any threat could put millions of birds at risk. If any of these so-called "critical" sites are lost or altered, the whole balance of the migratory process can be thrown off. A new WWF report, Climate Change Threats to Migratory Birds, identifies 15 of these critical habitats that are seriously threatened by global warming, and predicts the most threatened migratory birds to be shorebirds, ducks and geese.