I would like to respond to the letter from Tommy Spence in the Shetland News on 26 November (‘Reveal your Sources’), concerning the evidence for bird deaths as a result of windfarms. I’m sure that Philip Smith can defend his letter on bird mortality but I would like to make a few points if I may. First of all I would like to note that not only are collision impacts important but general habitat disturbance is an issue of equal prevalence in windfarm developments and is often neglected.
There are a large number of references in the literature to bird collisions and I will quote just a few. For example at three windfarms in Belgium it was reported that collision numbers varied from ‘0 to 124 birds per year with the mean number in 2002 being 24, 35 and 18 birds per wind turbine per year at the three farms’ (Natuur.Oriolus 69(3) 2003). In January 2006 the Brandenburg State Environment Office reported that ’69 red kite and 56 buzzard’ had been killed on windfarms in Germany – quite a lot for a rare protected species.
The Centre for Biological Diversity in the US reported that wind turbines at the Altamont Pass in California kill ‘an estimated’ 880 – 1300 birds of prey each year, including up to 116 golden eagles, 300 red-tailed hawks, 380 burrowing owls and additional hundreds of other raptors including kestrels, falcons, vultures and other owl species’. The wind farm operators dismissed this huge toll of raptors as being anomalous. However, further research on these deaths by Smallwood and Thelander in 2004 concluded that ‘adjusting for local relative abundance, the existing data indicate that most wind energy generating facilities have an equal impact on the local raptors’. Erickson (2001) states that ‘raptors comprise only 2.7 per cent of all turbine-related fatalities in the US and that protected songbirds comprise 78 per cent of deaths. This proportion would be even higher if it included legislatively unprotected species such as the Starling and House Sparrow’.
Of course it has to be remembered that often mortality rates are largely underestimated due to the inherent difficulty in collecting carcasses, especially those of small birds in the vicinity of the turbines. Also the numbers of bird deaths are often reported by the windfarm operators themselves who obviously wish them to be as low as possible in the first place. Langston and Pullan (2003) mentions that ‘even relatively small increases in mortality rates may have an impact on some bird populations, such as species at risk or large, long-lived species with generally low
annual productivity and slow maturity, such as raptors’.
Of course Viking Energy would argue that most bird deaths occur on windfarms sited on migratory routes. We are told that Viking Energy has done extensive research and consultation so that the siting of their windfarm will not occur on these projected migratory routes in Shetland. Therefore, we can be assured [they say] that there will be no bird deaths due to the turbines and everything will be ginger-peachy. End of story. But is it? Migration isn’t the only bird issue that has to be considered.
Many studies have shown that certain weather conditions (especially reduced visibility) increase the occurrence of collisions with human-built structures especially communication towers (Case et al 1965, Elkins 1988). So I think it can be assumed therefore that there will be increased bird mortality on the Shetland windfarm during the inclement weather often found in Shetland. For example, drizzle and fog impair visibility and cause birds to fly at lower altitudes in order to follow topographical clues. In some cases it has been shown that ‘birds will often divert as much as ~45° from their ‘preferred course’ in order to fly along such a ‘leading line’ (Richardson 2000). Even low cloud cover will induce migrants to fly at lower altitudes, which will lead to greater densities and as a consequence increase the risk of collision. Migrating birds also tend to fly lower when heading into opposing winds than when flying with tailwinds. It has been stated that ‘if there is a high proportion of fog days during migration at the project site, there may be increased risk of collisions (Kingsley and Whitten 2005). Many songbirds are nocturnal migrants, which is possibly why they are the most commonly birds to collide with windturbines (i.e.78 per cent).
One reason that has been put forward for why birds collide with wind turbines is that of ‘motion smear’ i.e. the birds just cannot see the blades even during good visibility. This effect is greater near the tips of the blade where the velocity is greatest and can exceed 250km per minute. This is especially relevant to raptors that soar and then once ground prey is spotted rapidly descend for the kill – only to be killed themselves as they fall into the blades. Predatory birds can also descend onto migrating flocks causing them to rapidly change course and be startled into the wind turbines. Certain birds that have aerial courtship displays would also be at risk and collisions of this nature have been observed at windfarms (Kerlinger and Dowdell 2003).
Even though collision death rates can have an immediate impact upon bird populations, disturbance caused by windfarms can lead to longer term effects and perhaps have a greater impact on birds. However due to the relatively recent advent of windfarms this area of windfarm impact has received little attention. But what information there is suggests that some groups of birds appear to be more sensitive to disturbance from wind energy facilities than other bird groups and indeed behavioural research on disturbance impacts is seriously lacking (Kingsley and Whittam 2005).
For example Larsen et al (2007) found that common eider in Denmark do indeed avoid flying close to offshore windfarms but that this behaviour may result in a reduction of habitat availability. Studies in Germany have shown that lines of turbines may act as barriers to movement of waterfowl and for other groups of birds (NABU 2004). Indeed, Exo et al (2003) noted that offshore installations might act as a barrier to seasonal and local migrations, disconnecting ecological units, such as foraging and roosting sites. Even though these are offshore windfarm studies there is no reason to suppose that that they will not apply to onshore facilities.
Disturbance can be an issue if the windfarm is located near important staging areas, where large numbers of birds concentrate to rest and feed (Kingsley and Whittam 2005). Sometimes, large numbers of birds may be forced to stop under emergency conditions such as rapidly deteriorating weather and it has been observed that non-resident birds, being possibly more unfamiliar with the wind turbines, have higher collision rates than non-residents. Richardson (2000) noted that the flight height of these migrants is often at the height of wind turbines and the flight path often concentrated into corridors leading to increased risk of collision. For example, birds like swans and some ducks typically climb only gradually and may remain low for a considerable distance after take off from a staging area. One can just imagine the horrendous scenario of large birds being unable to take off after they have alighted amongst a forest of windmills – remain trapped or chance being macerated.
Kingsley and Whittam (2005) noted that the greatest impacts that wind energy facilities have on breeding birds include habitat loss, destruction of active nests, obstruction of regular flight paths, disturbances caused by turbines or human activities around nesting sites and obstruction of important feeding areas. Reduced breeding populations have been noted at a few windfarms where breeding habitat was destroyed by the installation of turbines and where people and vehicles were continuously present in the area (Percival et al 1999). The Viking Energy project will encompass in excess of 60 square km of virgin Shetland wilderness and so there is every reason to believe that this kind of habitat disturbance and destruction will only be too common.
I think I have said enough but I hope I have made a few relevant points. I am not an ornithologist but even so I fail to see how the Viking Energy project will avoid causing damage and subsequent deterioration in the wild bird population of Shetland.
Remember that the threat to birds is a very small (but highly significant) part of the whole Shetland windfarm issue. If we include the negative effects on tourism, house prices, visibility, noise, quality of life, peat disturbance, run-off, environmental quality, Shetland’s wilderness – as well as debatable CO2 savings, the need for 90 per cent fossil fuel back up due to intermittence and the doubling of the price of electricity (Denmark experience) it is hard to understand how the project has got past first base.
Last week at PM questions, an English MP succinctly summed up the situation with windfarms. He said ‘windfarms are being opposed by local people but being imposed on them by the authorities’. This is exactly what is happening in Shetland. It has to be stopped.
PS Full list of references available by email.
30 November 2007
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