| Summary: | In spite of the detrimental influence of man upon nature, only about a quarter of the bird species in Finland have suffered a loss of area and/or become less abundant, whereas no less than a third has shown the opposite trend. The causes of these changes are discussed, particularly ( 1) the increase of' bird watching, which may create a false picture of expanding distribution ranges, (2) the amelioration of the climate since the end of the 19th century, and (3) the influence exerted upon nature by man and his domestic animals.
Though the spread and/or increase in numbers of many birds has coincided with the amelioration of climate, the degree of spread has in many cases vastly exceeded the northward displacement of isotherms. On the other hand, man's influence upon nature through changing land use has been profound, probably representing the most important cause of faunal changes today.
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