The Smøla Archipelago off the west coast of Norway, at (63°25′ N, 8°00′ E), has a particularly high breeding density of the white-tailed sea eagle, Haliaeetus albicilla. The EIA for the proposed wind farm indicated that it would affect the sea eagle negatively in several ways. Smøla wind farm as built consists of 68 turbines, and the second phase became operational in August 2005. A research program was initiated in 2003 to monitor the territory occupancy and productivity of sea eagles and their activity related to the turbines. These studies are now continued in a larger project within the Norwegian Research Council, with support also from the authorities, Statkraft and other stake holders.
Results from the first years of the project, until the second phase was operational in August 2005, are most probably affected by the activity associated with the development of the infrastructure within the wind farm (roads, power lines and buildings), foundations for the turbines, and the erection of the turbines. At times the activity was intense in most of the area for phase 2, while it was less in the area of phase 1. From 2006 the results will more and more reflect the effects of the whole wind farm in its normal operational phase.
There were 14 to 16 sea eagle territories identified in the wind farm area before construction, but more detailed studies have shown that a minimum of 19 pairs were breeding in this area. So far at least five pairs have left their territories, without any sign of reestablishment elsewhere on Smøla. If they are not able to find optimal nest sites outside the wind farm, or if new pairs do not enter the vacated territories, then one effect of the wind farm will in the long term be a lower breeding population on Smøla.
Reproduction has been lower for the sea eagles in the project period than before construction, both inside and outside the wind farm. An important factor may be due to pairs still occupying and defending their nest sites within or close to the wind farm, but with a low breeding performance. If the low breeding output and the increased mortality continue, resulting in problems with recruitment of new breeding birds to the breeding population at Smøla and nearby areas, the wind farm could become a sink area.
After phase 2 was operational, ten fatal collisions between sea eagles and the rotor blades of the turbines were recorded between August 2005 and March 2007. Four fatalities were recorded in just 1 week during the 2006 breeding season. Both breeding adults and fledged juveniles are among the deaths, including three of the five young fledged in 2005 within the wind farm plus a 2-km buffer. Before February 2006, there were no formal searches for corpses and dead birds were incidental finds, so the total may be greater. From late summer 2006, a trained dog has been deployed to detect and mark the location of dead birds.
Post mortems by the Veterinary Institute have shown that all sea eagles show clear signs of a heavy blow to their bodies. The damage resulted in either immediate death or immobilization. They were all injured on their body or inner part of the wing, and some were cut into two or more pieces. As no birds have been found dead with injuries only on outer parts of the wing, some fatalities where the birds have not died or been immobilized may have been undiscovered. Some sea eagles have been found dead a short time after days with high soaring and termic activity of the eagles.
The results from the satellite-tagging of nestlings of fledgling white-tailed sea eagles show that the median time spent in the wind farm was c. 90 days (to c. 1 September) but with large variation between individuals. One of 15 satellite-tagged juveniles was killed during this period. Of the 12 juveniles with data sufficient for evaluation, two were killed in April in the year after tagging. The juvenile mortality seems to be higher at Smøla than in other parts of the country. Some juvenile birds disperse far – movements up to Lofoten/Vesterålen have been shown – while others stay in their natal area. Localising of transmitters several days in a row from the same position has helped in finding turbine-struck birds. The satellite telemetry has also supplied new knowledge on the use of night-roosts in the vicinity of the park. The juveniles seem to spend little time within the central parts of the wind-park in the time after fledging, but taken into account that the tags only give one position per hour many park crossings may pass undetected. The limited material so far seems to indicate increased collision risk during spring, when many of the birds return to their natal area. Females seem to move farther away from the park than males.
Monitoring of activity at nests by use of video cameras was initiated in 2006, and results so far show that the frequency of sea eagles flying to and from the nest is highest in the morning and evening. This is in accordance with what is known about where and when the sea eagles at Smøla are searching for food. Information on how the eagles use the terrain when they enter or leave the nest site may help to improve collision risk models.
DNA analysis was carried out for feather samples from chicks born in 2006, moulted feathers from adult individuals on the nest, and tissue samples from several of the dead sea eagles. These analyses gave no match with DNA samples from the three dead eagles found in early May 2006 and samples from the nests. This was most probably due to the lack of DNA samples from all territorial sea eagles at Smøla.
The DNA analyses will over time allow detailed mortality assessments, and it should be possible to address whether the mortality among breeding eagles in or close to the windmill park is higher than in the rest of the sea eagle population. The DNA approach has already revealed several interesting details on the breeding ecology of the sea eagle.
There are at least four ways in which long-term effects on the population level at Smøla may be manifested:
- Reduced breeding population, if birds no longer breed within or close to the wind farm or do not succeed in raising young.
- An increase in adult mortality, due to collisions with the wind turbines.
- Reduced breeding success (at least as long as some pairs try to hold their territories within or close to the wind farm).
- Increased juvenile mortality (poor post-fledging survival due to collision with wind turbines).
Results so far indicate some factors it may be important to focus on when new wind farms are planned, if we want to avoid some of the negative effects on birds as we have seen for the sea eagles at Smøla. Perhaps most important, given further proposals for wind farms along the Norwegian coast, in other areas of high density of breeding white-tailed eagles, is to focus on the cumulative impacts on the population from multiple wind farms along the coast.
This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.
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