a high calcium content. Alternative energy Over the past 30 years residents have begun to use solar collectors for hot water. With about 2,400 hours of sunlight per year, Skopelos has the potential to increase its solar energy use and to develop alternative sources for energy which make use of a frequent and steady northerly wind. Major construction and mass tourism development projects for hotels and tourist housing have not yet embraced the concept of alternative resources. Most recently built projects rely on electricity generated on the mainland, even for hot water. Wildlife Birds Skopelos has a variety of fauna – including about 60 bird species including migrants. There are several birds of prey, most common being the Eleonora's falcon, the Eurasian scops owl and the common buzzard. Also to be seen are kestrels, eagles, and vultures, and very obvious throughout the island is the hooded crow. Occasionally grey herons and common kingfishers and, more commonly, the great cormorant, the herring gull and the yellow-legged gull are seen along the coast. In March 2007 the Municipal Authorities cleaned a wetland habitat near the town beach at the outlet to the sea of Skopelos' only permanently flowing stream. The area had been home to frogs and the birds that fed on them. Mammals The Northern Sporades are one of the prime breeding areas of the Mediterranean monk seal, an endangered species. The main threat to the seal population is human activities. Often deliberately killed or accidentally caught in fishing equipment, its food sources are declining also. In addition, marine pollution and uncontrolled tourism are causing the destruction of the seal's natural habitat. The establishment in 1992 of the National Marine Park of Alonnissos-Northern Sporades was an effort to protect this species by restricting human encroachment on seal breeding areas. Wild land mammals include stone martens, brown rats and house mice, the southern white-breasted hedgehog, bats and, though declining in numbers, European hares. A mating pair of fallow deer have been privately reintroduced to the island. A population of feral cats exists in and around areas of human habitation. Reptiles The island is home to a variety of reptiles. The Balkan pond turtle can be found near fresh water along with the Greek marsh frog, though this habitat is slowly disappearing due to development. The Erhard's wall lizard is seen regularly in daylight in warm weather and the Mediterranean house gecko at