Changes in the bird fauna in Finland and their causes

Abstract

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 19^th 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.