This is a guest article by Jan Södersved. It originally appeared in the Finnish language in the Birdlife magazine, Linnut.
Wind Farm Safety by Bird Radar
Finland’s first offshore wind farm is located in a place where it should not be because of the birds – on a significant bird migration route in front of Tahkoluoto near to Pori. Among other things, bird detection radars are used in an attempt to reduce the effects of wind turbine farms on bird populations.
The road which snakes its way through Tahkoluoto ends at Kallioholma. In Pori you cannot get any further out by road than that. Local enthusiasts have been following bird migration here ever since a land connection to the island was built at the beginning of the 1980s.
Now waves slam against the shore, and now and then in gusts the wind speed reaches 20 metres per second. It’s almost difficult to remain standing, and my eyes begin to water when I have been looking at the sea with binoculars for a moment. Doesn’t look as if birds are on the move in this weather. I try to get some protection from the wind behind a nearby windmill. More windmills rise from the sea. Their blades rotate in a wide circle at a height of nearly one hundred metres. The nearest mill grinds out electricity about half a kilometre away, and further out there are ten more mills.
Echoes on the Screen
Photo Credit: JAN SÖDERSVED
Petteri Mäkelä tracks information transmitted by the radar onto the computer screen. The red dots are flying birds.
A hut has been placed at the end of the island and an observation platform has been built on its roof. I go up there, but very soon I climb down again. In clearer weather it would be nice to look far out over the sea, but right now I’m thankful to simply get into the hut and out of the wind. In the hut there is a veritable landscape office: a chair, desk, computer and window, through which you can see the open sea.
Petteri Mäkelä, environmental engineer and bird enthusiast, who works for Suomen Hyötytuuli Oy, the company responsible for Finland’s first offshore wind farm, sits by the computer and introduces the Tahkoluoto offshore wind farm on the big screen. "Its 11 power plants produce about 155 gigawatt hours per year. This amount of energy can heat over 8,500 homes", Mäkelä tells us. The turbines have now been running for a year.
The turbines and the areas around them appear as grey blotches on the map on the screen. In addition, the map shows smaller red and violet circles and lines. They are pictures of radar echoes, in practice mainly birds and their flight routes.
The radar, which is transported on a trailer, has been securely anchored near the hut. It has stood there for two and a half years, defying sprays of salt water, winds of up to 30 metres per second and temperatures of minus 20 degrees Celsius. Two antennas rotating in different directions produce three-dimensional spatial information. Similar radars are used at airports.
Concern About Birdlife
It was decided to install bird radar at Tahkoluoto because it was not possible to obtain a building licence for the offshore wind farm with the original design. The wind farm was going to be installed on the migration route of species of large birds. In addition, the planned wind farm borders on the Gummandoora archipelago, which is part of an important international bird park and belongs to the Natura 2000 network.
In relation to local birds, there was special concern in Finland regarding the highly endangered black-backed gull. The nesting population of the area is 150 pairs, and a further 50 pairs nest in nearby areas.
Another concern was the white-tailed eagle, classified as endangered. Bulky soaring birds of prey are not good at avoiding wind turbines and contribute to bird strike incidents. Badly located wind farms have been deadly to white-tailed eagles in Norway, golden eagles in the USA and griffon vultures in Spain. Three pairs of white-tailed eagles nested within a range of ten kilometres of the planned wind farm, and the farm area also cuts across their main migration route.
Finally, the building permit for the wind farm was granted, despite the fact that it is on the main migration route of several species, which is contrary to the guidelines of the Ministry of the Environment and international recommendations. The revised permit conditions included a bird radar, the intention being to prevent or at least reduce accidents with birds. In the case of Tahkoluoto, the objective was that windmills would not cause harm to the black-backed gull and the white-tailed eagle.
What Does the Radar Tell Us?
The use of bird detection radars in wind farms is not new. For instance, in California most California condors have GPS transmitters, and the information they send is also used to prevent collisions with wind turbines. A condor approaching a wind farm sets off an alarm, and an employee can, if necessary, turn off a specific turbine. But the black-backed gull and the white-tailed eagle do not have transmitters. How can the radar tell what bird is approaching the wind farm?
The radar classifies birds as big, medium and small. It detects big birds even as far away as ten kilometres, and small ones at least two and sometimes three kilometres. Determination of the size can be made by the angle at which the bird approaches the radar. Also, dense flights of small birds can mistakenly be interpreted as bigger birds.
In addition to its size, the radar also shows the speed, altitude and predicted direction of the bird. From a three-dimensional picture you can also perceive the flight mode, for instance soaring. By combining this information with visual sightings by birdwatchers and information about the weather, it is possible to learn to recognise certain echoes.
The Tampere University of Technology is developing a program which compiles a picture using the information produced by the radar. The radar sends location coordinates to the camera and the video camera, to which a 500mm telephoto lens has been attached, aims at the location and focuses at the desired distance. At this time the results are still unclear. The challenge is to focus on the right bird, when the distance can even be 1.3 kilometres.
The white-tailed eagle can be identified quite reliably based on its size and way of flying, and many groups of species can be defined merely based on flying speed. At Tahkoluoto, gulls typically fly at about 25 km per hour, cormorants twice as fast and goldeneyes hurtle along at about 83 km per hour.
A Turbine Stop Command
The radar software information is transmitted to each wind turbine. When the turbine receives information about an approaching object which is identified as a white-tailed eagle or black-backed gull, the rotor gets a stop command and the blades stop moving in ten seconds. In that period of time the eagle flies a full 100 metres. The turbine switches back on automatically a couple of minutes after it has ceased to receive approach warnings. This can help reduce the number of bird deaths caused by the turbine. In the past year each turbine in the area has been stopped about 200 times in this manner. Species other than the white-tailed eagle or black-backed gull do not stop the turbine.
When examining objects, the time of year and the hour of the day are taken into account. For instance, it is expected that there will be no black-backed gulls in the area between mid-September and the end of March. More precise dates are confirmed based on when the black-backed gulls have migrated. "It is easy for me to go and check every day to see if the gulls are still around or have left", says Mäkelä.
Mäkelä has been observing the bird population in the area for a long time and estimates that every year around 300,000 birds migrate through the wind farm area during the day. According to radar observations, the number of birds on the move at night is much bigger. A slight surprise has been that large numbers of birds can also fly in thick fog. Maybe they fly above the fog cloud.
So how many birds will crash into the wind turbines of the new wind turbine farm? In spite of active monitoring, only once has a bird been seen crashing into a wind turbine. A bird counter who was in a boat observed a gull flying out of fog straight into the blades of a turbine. Unfortunately, this particular victim was a highly endangered black-backed gull, about which there has been a lot of concern in the project. Crashes will probably happen particularly in bad weather or at night. Mäkelä estimates that crashes will happen very rarely.
According to research, the number of birds crashing into wind turbines varies considerably. The biggest effects on crashes are usually found where wind farms have been built on the coast or on the shores of great waterway routes. It has been estimated that in those places 15 birds a year on average crash into each farm. The estimate takes into account birds bigger than thrushes, because it is difficult to verify crashes of small birds. So the number of crashes per individual turbine is quite low. However, small numbers can add up to a significant number on a population level, if there are many wind farms in locations that are of importance to the annual life of birds, such as nesting and resting areas, and main migration routes.
Black-backed Gulls in Intensive Observation
Photo Credit: JARI KOSTET
The number of black-backed gulls has declined sharply. The area in front of Tahkoluoto is an important nesting and feeding area for the black-backed gull.
The water permit for the wind farm requires mapping bird nesting places on the islands in the area, counting rest landings and monitoring spring and autumn migrations. In spring, migration through the area consists of 20,000 eiders, 10,000 loons and tens of thousands of blackbirds and velvet scoters. In summer, up to 9,000 eiders and 5,000 golden eyes gather here to moult. In the autumn and sometimes even in winter it is possible to see as many as 5,000 common gulls.
White-tailed eagles and black-backed gulls are monitored more closely. The chicks’ movements were monitored last summer for four weeks after they began to fly. In the next two years the chicks will be monitored for at least two weeks. Black-backed gull development will be studied over a much larger area, to clarify how the wind farm effects for instance chick production and population development.
Nesting litters of black-backed gulls will be counted from in front of Luvia to the shores of Merikarvia, but special monitoring is on Kaija Island in front of Tahkoluoto and in Revel of Merikarvia. Smaller comparison samples will be gathered in the archipelagos of Eurajoki and Kustavi.
The black-backed gull has had very poor nesting litter results and the number of couples is in sharp decline. The birds have partially moved away from the area. One reason is thought to be harassment and prey pressure from the white-tailed eagles. According to studies, wind farms drive out birds which are resting or nesting, but this varies greatly by species: some avoid the farms, some don’t. Monitoring a larger area will allow us to evaluate which effects are due to wind farms and which are due to other factors.
In accordance with the building permit, radar monitoring must be continued for at least five years after start of production, that is until 2022. What will happen after that is still an open question.
Birdlife’s wind power policy:
Wind farms are not to be built:
- in areas important to water and wetland birds
- in areas designated for environmental protection
- in nesting and resting places of endangered species
- near the nests of big birds of prey
- on regular flight routes of big birds
- in shoals in the sea, concerning which there is not enough bird knowledge
- in areas of natural marshes, forests and fells
- see more: https://www.birdlife.fi/suojelu/vaikuttaminen/tuulivoima/