The fatal impact of a white-throated needletail with a wind turbine in Scotland (1) raises serious concerns, with ramifications far beyond the sad loss of a single, spectacular vagrant. As a rare visitor, this individual bird was being very carefully observed, and thus there was a far higher chance of a turbine impact being detected than is the case for most small birds. Only a minuscule fraction of birds are intensively monitored in this way, and if the movements and fates of many other individual birds were being monitored, then what appears to be a rare event might prove to be frequent – or indeed probable. The death of this needletail should remind us that numerous small birds are being hit by turbines without detection or raising alarm. However, other hirundine deaths have already been documented amongst Europe’s wind turbines (2).
The needletail encountered a small, lone turbine. On the face of it, this is highly unlikely – unless the bird was actively attracted to the vicinity of the turbine. Indeed, some insects are attracted to wind turbines, and some bats are attracted to their deaths by unknown features of the turbines – possibly the food concentration around them (3, 4, 5). Remarkably, there are reports of bats commuting to wind turbines up to 14 km offshore for such food resources, as well as others stopping, perching and feeding around them during migration (4). This attraction exerted by wind turbines extends their ecological footprint to new, unsuspected dimensions.
We hypothesise that hirundines (including swifts, swallows, martins, swiftlets and needletails) might also be attracted to insects flying around these machines – onshore and offshore. Indeed, awareness has already been raised about the potential attraction of insectivorous birds to wind turbines (5). Reports (5, 6) that hirundines can comprise a third of turbine victims in Sweden and are being killed by domestic microturbines in Britain merit further investigation. Another consideration is that certain landscape features and air flows might attract both wind farm developers and hirundines, putting them on a collision course as they do with raptors.
We propose that wind turbines, let alone wind farms, may create extensive population sinks which could deplete and exterminate populations of birds and bats. We doubt the woeful amount of independent monitoring of turbine impacts would be capable of detecting this threat in most regions or for most species.
In the circumstances, a precautionary approach would be particularly appropriate in areas with populations of already threatened endemic hirundines, bats and other species – as in Seychelles or the Mascarenes for instance. For such areas, irreversible global extinction might be caused by wind turbines, yet even the highest standards of monitoring (including videos and radio transmitters) might be insufficient to alert us in time. We predict the extinction legacy of wind turbines will become an increasing source of concern, as ecological traps are set in vast numbers across the planet.
Clive Hambler (Lecturer in Biological and Human Sciences, Hertford College, University of Oxford)
Mark Duchamp (President, Save the Eagles International; Chair, World Council for Nature)
(2) – Photos of a sample of bird fatalities due to wind farms, including hirundines, from the Save the Eagles International website: http://savetheeagles.wordpress.com/birdkill-pictures/ 
– More pictures of birds killed by wind turbines may be seen here: http://savetheeaglesinternational.org/multimedia/ 
– And there are many more.
(3) – Video monitoring of bats flying between turbine blades, showing some getting struck: http://www.epaw.org/multimedia.php?article=b6 
(4) – “We recorded 11 species (of a community of 18 species) flying over the ocean up to 14 km from the shore.” Ahlén, I. et al. (2009). Behaviour of Scandinavian bats during migration and foraging at sea. Journal of Mammology, 90, 1318-1323
– “The bats did not avoid the turbines. On the contrary they stayed for shorter or longer periods hunting close to the windmills because of the accumulation of flying insects. Hunting close to the blades was observed, why the risk of colliding might be comparable to land-based turbines. Bats also used wind turbines for resting. Insects were collected at places and times when bats were observed feeding.” Ahlén, I. et al. (2007). Bats and offshore wind turbines studied in southern Scandinavia. Swedish Environmental Protection Agency. Report 5571. http://www.naturvardsverket.se/Documents/publikationer/620-5571-2.pdf 
(5) – “Increased risks depend on insect hunting (swifts, swallows), carrion search (crows, ravens, some raptors), and hangwind gliding (red kites, eagles, and buzzards).” – Ahlén, I. (2010). Fågelarter funna under vindkraftverk i Sverige. Var Fågelvärld, 4/2010, 8-12 http://www.slu.se/PageFiles/8390/artiklar/BirdsWindPowerVF2010.pdf 
– Long, C. V. et al. (2011). Insect attraction to wind turbines: does colour play a role? European Journal of Wildlife Research, 57, 323-331 http://peer.ccsd.cnrs.fr/docs/00/62/51/48/PDF/PEER_stage2_10.1007%252Fs10344-010-0432-7.pdf 
(6) – “Almost one third of the birds (killed) were swallows and swifts, species that like bats hunt flying insects”. Ahlén, I. (2002). Wind turbines and bats – a pilot study. Report to Swedish National Energy Association. http://publikationer.slu.se/Filer/08WindBatFinalReport.pdf