Forests, chiefly pine, spruce, and birch, are economically the most significant flora. There are more than 1,100 native species of higher plants; flora is richest in southern Finland and the Åland Islands. Of 22,700 species of fauna, more than 75% are insects. At least 60 species of mammals are native to Finland. Fur-bearing animals (otter, marten, ermine) are declining in number, while elk, fox, and beaver have increased. Of some 248 species of breeding birds, the best known is the cuckoo, the harbinger of spring. Of some 66 species of freshwater fish, 33 have some economic importance; in fresh waters, the perch, walleyed pike, great northern pike, and others are plentiful. Salmon remains the favorite of fly rod enthusiasts.