Population dynamics in white-tailed eagle at an on-shore wind farm area in coastal Norway


Title: Population dynamics in white-tailed eagle at an on-shore wind farm area in coastal Norway
Authors: Dahl, E.
Publication Date:
January 01, 2014
Thesis Type: Doctoral Dissertation
Academic Department: Biology

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Dahl, E. (2014). Population dynamics in white-tailed eagle at an on-shore wind farm area in coastal Norway. Doctoral Dissertation, Norwegian University of Science and Technology (NTNU).

Collision with turbines and disturbance leading to loss of or reduced habitat quality are the two main impacts from wind energy development on birds. In addition, wind farms can act as barriers to birds. The conflict between birds and wind farms are highly site-, season- and species-specific. Among the most vulnerable group of birds are the raptorial species. Large soaring birds have proven to be particularly vulnerable to collision with turbines. In this thesis I aimed to test if a 68-turbine wind farm on the island of Smøla, mid-Norway, was in conflict with a population of white-tailed eagles breeding at high density. The white-tailed eagle is a species with slow reproduction, long life span and high annual survival rates. These demographic characteristics make them particularly vulnerable to increased mortality. I found that the white-tailed eagle population was affected both by disturbance and collision mortality. Eagles did not significantly change their flight behavior when inside the wind farm, possibly explaining the relative high collision mortality. Territories close to the wind farm experienced reduced breeding success in the post-construction period compared to pre-construction. The effect was due to mortality and birds being displaced from their territories within the wind farm. Also, mortality among both sub-adult and adult birds was higher for birds with origin close to turbines compared to those originating further away from turbines. The growth rate in the population was reduced by the wind farm development, with the part of the population breeding close to the wind farm being most affected. Also, expected average age of adult birds in territories close to turbines was lower than for birds further away from turbines. Among the demographic parameters, adult survival was, by far, the most influential to the population growth rate. There was a clear spatial component in the impact from the wind farm on the white-tailed eagle population. The impact from mortality had a wider spatial component compared to the impact from disturbance. I traced the impact from increased mortality among adult eagles in territories out to 5 km from the turbines, while the reproductive success was reduced in territories out to 1 km from the turbines. It is therefore highly important to take into consideration both disturbance and mortality when planning future wind farm. As a last option, compensation measures can be an effective tool if avoidance and mitigation of avian conflicts in wind farms are non-efficient or too expensive. Electrocution prevention measures at a nearby power line were identified as a potential compensation project, compensating for white-tailed eagle mortality in the Smøla wind farm.

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