Future changes in bird species distributions can be estimated with the help of climate models

Climate affects species distributions

Climate is one of the factors determining whether an area is suitable for an individual species. For example an animal species can thrive only if precipitation is high enough for the growth of the plants which the animal feeds on. Species themselves may have temperature limits above or below which the species' well-being is disturbed. [1] The distributions of Finnish bird species are largely defined by differences in climate in different parts of the country [2].

Models for species distributions take advantage of climate models

The Impact scenarios of climate change mapping tool in Climateguide.fi presents how climate change could alter distributions of bird species in Finland. Simulated distributions of the species were prepared with bioclimatic envelope models [1].

Bioclimatic envelope models identify present-day climatic conditions where a species currently occurs. The models can then be applied with climate scenarios to identify shifts in areas with suitable climate conditions in the future. The simulated new range of a species would be where the suitable climate has shifted. Likewise the current simulated range would cover the area where the climate is suitable for the species at the moment.

Bioclimatic models usually do not take into account other environmental conditions that determine the suitability for a species. For example, land-use might be such that it prevents the formation of suitable habitats even though climate would be suitable. Therefore bioclimatic models based only on climate variables may exaggerate the ability of species to colonize new areas. [1], [3] On the other hand small scale variation in topography can preserve suitable microclimate patches for the species even if the climate in general would become worse. Variation in topography and vegetation are often added into bioclimatic models to improve their predictive quality [2], [4]. However, the model which has been used in Climateguide only uses climatic variables [1].

Information of current distributions is based on observed breeding statuses

Four bird species that breed in different habitats were chosen from the model of Virkkala et al. to be presented in the Impact scenarios of climate change mapping tool: Red-throated Pipit (Anthus cervinus), Rustic Bunting (Emberiza rustica), Brambling (Fringilla montifringilla) and Common Greenshank (Tringa nebularia). Rustic bunting and Brambling are forest species while Red-throated Pipit and Common Greenshank are mire species. Rustic Bunting, Brambling and Common Greenshank have currently fairly large ranges in Finland while Red-throated Pipit is restricted to northernmost mires. [5]

Observed bird species ranges were obtained from the three Finnish breeding bird atlases of the Finnish Museum of Natural History and the Ministry of Environment [VAL11], which contain information of bird species breeding statuses on a 10 x 10 kilometer grid covering the whole of Finland. The observations have been collected in three periods, 1974-79 for the first, 1986-1989 for the second, and 2006-2010 for the third atlas. For the uses of the mapping tool in Climateguide data of the first two atlases were combined into one time period, 1974-1989. Three breeding statuses "possible", "probable" and "confirmed" used in the atlases were aggregated to a single class "presence". Grid cells with the statuses "observed, but un-probable" and grid cells without observations were mapped as being outside the species distribution. This resulted in maps that distinguish the following areas:

• Area outside distribution during 1974-1989 and 2006-2010

• Present during 1974-1989 and 2006-2010

• Appearance during 2006-2010

• Disappearance since 1974-1989

Bioclimatic envelope models exploit climate scenarios

Virkkala et al. combined in their bioclimatic model data of the first two atlases for Finland with breeding observations from Finnmark, northern Norway, (1977-1986), using the same aggregation of breeding statuses as in Climateguide,fi explained above. Historic (1971-1990) and future climate data were obtained from the ALARM project. The HadCM3 climate model of Hadley Centre was used for constructing climate projections. Climate projections were prepared for two time periods, 2021-2050 and 2051-2080, with a moderate emission scenario (SRES A2) and for 2051-2080 with a low emission scenario (SRES B1). [1], [6], [7]

To match the breeding data with climate data, Virkkala et al. transferred breeding data to a 10' x 10' resolution into distorted rectangles [1]. In The Impact scenarios of climate change mapping tool of Climateguide.fi the simulated ranges are interpolated back to the 10 x 10 kilometer grid as this made it easier to create the maps in the portal.

Maps of simulated ranges are depicted in Climateguide.fi as the following areas:

• Area outside the simulated distribution during all periods

• Present in baseline (1971-1990) and future

• Future expansion relative to 1971-1990

• Future contraction relative to 1971-1990

The simulated changes in the distributions of the four bird species can be studied in more detail in the mapping tool of Climateguide.fi (figure 1).