A survey of the bird populations in Oldfjällen in Jämtland county, Sweden, was initiated in 2003 prior to the construction of a wind-farm on two adjacent hills, Storrun and Frösörun by the lake Övre Oldsjön. After a gap in the surveys in 2004, comprehensive studies were continued during 2005–2008, prior to the construction. The construction-work started during autumn 2008, and the turbines were erected during 2009. Power production was started during the autumn of 2009. The post-construction bird studies were carried out in 2010 and 2011.
This report summarizes all the studies that were performed before and after the construction of the wind-farm. Many of the separate studies were made using a BACI method (Before-After-Control-Impact) enabling comparisons of the situation before and after development, using a control area. In addition, a study of collision rates and scavenger removal rates is reported. As expected, the movement and migration of birds over Storrun was of rather limited magnitude. Although the majority of observations during the investigated periods spring and autumn are assumed to be migrating birds, larger flocks of birds are rare in the area. Ca. 20 % of all the birds that passed through or near the wind-farm area flew in heights comparable to the rotor-swept zone. However, more than 40 % of the raptors and waders passed through in that zone, which implies a collision risk. These two groups of birds have shown to be particularly prone to collisions with rotor blades in other studies.
The studies using territory mapping, showed that small passerines were dominating in the study plots. The number and densities of territories declined post-construction, but as this was even true in a nearby reference area, we were not able to relate this decline to the wind-farm as such. The largest decline was however noted in the study plot most affected by constructions, and it had a significant decline in number of territories per species.
A pair of red-throated divers that bred in the study area before the construction disappeared completely after the construction-phase. Observations of ducks, not breeding in the study area, also ceased in the territory mapping after construction. The number of territorial willow grouse also declined considerably post-construction, but as no pairs bred in the reference area, we have no comparable control. The displacement effect of roads, towers and installations could only be tested for two passerine species; the willow warbler and the tree pipit. We were not able to prove a significant displacement on either of these species. The line-transects of birds showed a downward trend both in number of species and of individuals during the course of the study. This is in line with what was shown in the study plots using territory mapping.