Long-term bird population changes in the protected areas of Finland under climate change
Climate warming causes poleward shifts of species ranges and populations. Also in Finland both ranges (Ref. 1) and mean weighted densities (2) of species have shifted northwards during the past 40 years. Moreover, climate change and other human influences such as land use and hunting may cause changes in population sizes. Protected area (PA) network is one of the key instruments to maintain biodiversity in a changing climate and alleviate abrupt changes in species distributions and densities (3). In order to analyze the ability of nature reserves to maintain populations we compared the observed changes of bird species in over 250 protected areas in Finland between two time slices, 1981-1999 and 2000-2017. The data are large with over 9,100 km of line transects censused in the first and 10,400 km in the latter period. Between these two periods, the total bird density in protected areas declined by about 10%. The decline in total bird density was the largest in the southern PAs showing an overall northward shift in mean weighted bird density in the PA network. In particular, long-distant migrants overwintering in Africa and in Southeast Asia (e.g. willow warbler Phylloscopus trochilus and rustic bunting Emberiza rustica) and northern species (e.g. brambling Fringilla montifringilla) declined considerably, while many southern species increased. Both decreased and increased species showed a pattern of northward shift in their abundances in the PA network in line with the climate change predictions. Protected areas have been established particularly to preserve old-growth forests and many resident, non-migratory species preferring these habitats either remained stable (e.g. Siberian tit Poecile cinctus, Siberian jay Perisoreus infaustus) or even increased (three-toed woodpecker Picoides tridactylus) in PAs. This shows that by protecting old-growth forests it is possible to enhance preservation of species in these habitats even under changing climate. However, global climate change and direct human influence appear to affect migratory birds considerably, causing the decline of populations and impoverishment of bird communities in the boreal PAs.
Our work is part of three-year project of evaluation of protected area network in the changing climate (SUMI).
(1) Virkkala, R. & Lehikoinen, A. 2017: Birds on the move in the face of climate change: High species turnover in northern Europe. Ecology and Evolution 7:8201-8209.
(2) Virkkala, R. & Lehikoinen, A. 2014: Patterns of climate-induced density shifts of species: poleward shifs faster in northern boreal birds than in southern birds. Global Change Biology 20:2995-3003.
(3) Virkkala, R., Pöyry, J., Heikkinen, R.K., Lehikoinen, A. & Valkama, J. 2014: Protected areas alleviate climate change effects on northern bird species of conservation concern. Ecology and Evolution 4:2991-3003.