Many wetlands support great concentrations of individual wildlife species (e.g. waterfowl) and a significant diversity of endemic vertebrates such as fish. Large number of birds and high energy-demanding migratory birds choose wetlands especially because they sustain a great availability of prey populations (e.g. crabs).
Birds may lose between 10% and 50% of their body weight on their migration. For example, the Blackpoll warbler flies 86 hours nonstop over the ocean from the northeastern USA. to South America. The metabolic equivalent would be like a human running 4-minute miles for 80 hours.
In North America alone, some 5 billion birds – more than 350 species – travel overhead each season.
The Wild Birds Directive (Council Directive 79/409/EEC on the conservation of wild birds) is the Community's oldest piece of nature conservation legislation. It creates a comprehensive scheme of protection for the Community's wild bird species, covering the conservation of the most important bird habitats as well as controls on hunting and other forms of exploitation. Migratory birds may not be hunted during their migration back to their rearing grounds. The Directive also includes a requirement for Member States to classify a network of protected areas (known as special protection areas or SPAs) for the most threatened species. Within SPAs, bird habitats must be protected from deterioration. The Directive also requires habitat conservation measures outside SPAs.