Three habitats can be seen along this route:
The Cantabrian Sea
The Cantabrian Sea – the southern end of the Bay of Biscay – forms part of the Atlantic Ocean. Relatively cold deep waters, a wind that does not stop blowing strongly and a pronounced swell may seem an inhospitable environment for wildlife, but appearances can be deceptive, seeing as the Cantabrian Sea is brimming with both animal and plant wildlife. Its importance for fishing confirms the fact. A large number of seabirds that breed on the coast depend on the sea for their food, especially the yellow-legged gull, the shag and the storm petrel. The Cantabrian Sea is also important as a wintering and transit area for seabirds coming from the north such as the gannet, the kittiwake, shearwaters, skuas, terns, petrels, scoters and divers, to name only some.
Coastal cliffs and lowland
The narrow strip where the sea and the land meet is a robust, dynamic habitat. Steep cliffs have been formed where the force of the waves and the wind crash continuously against the rocky land, some of which are over 100 m high. Niches, ledges and cracks in these more or less vertical walls constitute the breeding substrate of the abundant yellow-legged gull and of the rare storm petrel and shag, as well as that of the peregrine. Behind this “front line” extends the flat lowland, partly covered by a thick blanket of heather. This is the habitat of stonechats and windchats, warblers, larks and the red-backed shrike, among other species. In the migrating season, large flocks of passerines usually alight on the coastal strip to rest and recover their strength.
Beaches and river mouths
The cliffs along the coastline can be seen to be broken up by different types of beaches –of sand, gravel or rock – as well as by the mouths of small rivers such as the River Piles or Avilés Estuary, where, due to the ceaseless work of the tide, banks of sand and mud form teeming with invertebrates. These flat, open, peaceful sites at the water’s edge usually provide optimum conditions for groups of gulls, terns and waders to feed and rest, especially outside of the breeding season.