Northward density shift of bird species in boreal protected areas due to climate change

摘要

Species ranges are expected to move latitudinally poleward because of the warming cli- mate. We asked whether northward patterns are observable also in population densities of land birds in Finnish protected areas such that temporal population changes would be most pronounced toward species range boundaries. We compared population changes of north- ern species, southern species, and species distributed over the whole country from 1981– 1999 to 2000–2009 in 96 protected areas. Northern species showed the greatest decrease in southern Finnish protected areas, and southern birds increased most in northern Finnish protected areas. Among species distributed over the whole country, there were popula- tion density shifts toward northern Finnish protected areas. Two thirds of the species that decreased most were northern, whereas many of the species showing the greatest increase were southern habitat generalists. The results show that there are already northward density shifts occurring that probably precede future species range shifts.