Wind Turbines, Bats and Birds
This information was sent to us
by Ivan Buxton, who lives at Ashwater. The photo is of a tangled
hedgerow near Ashwater.
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Bats use echolocation techniques to detect and hunt for prey and as creatures of habit regularly follow field boundaries, hedges, tree lines and watercourses in search of insects.
They also commute between roosts and feeding grounds. Utilising both winter and summer roosts at differing locations whilst females create nursery roosts where they raise their single off spring, but only during a successful breeding year.
Many winged invertebrates are weather dependent and will rise and fall within their habitat according to humidity and temperature levels, which is why during damp and overcast summer conditions swallows, martins and swifts are seen carrying out low level hunting manoeuvres and then fly high in the sky on clear warm days. They are hunting insects.
The antics of these birds are clearly visible, but because of the largely nocturnal habits of bats, who also follow a similar hunting pattern, their pursuit of prey is mostly unseen by human observation. They can, however be tracked by use of electronic equipment.
Although it is likely that all flying creatures are prone to collision with wind turbine blades and towers some species are more vulnerable than others. In particular Noctule bats, which are known to switch off their echolocation once they have caught their prey and then feed circling around and around, invariably at rotor blade height.
Modern wind turbines have caused the death of large numbers of birds and bats, especially if placed in the path of migratory species. They also have the potential to create habitat displacement and interrupt breeding, feeding and commuting patterns.
For example removal of only a short line of hedgerow to permit an access track for delivery and erection of turbines can fatally interfere with foraging routes. It is therefore essential that when planning to construct a ‘windfarm’ that a proper ecological survey is carried out embracing all seasons of the year over a period of several years to allow for fluctuations in weather patterns and food supplies.
Birds do not hear as well as it might be supposed and experiments have concluded that as sound and vision work in concert birds neither see nor hear turbine blades until it is too late to avoid collision. Turbine noise has to be about 1.5dB above the background noise for birds to detect it as a source of potential danger and the blades become ‘invisible’ to them due to motion smear.
Large birds such as raptors, ducks, geese, swans and gulls appear to have suffered most from turbine impact, although smaller bird carcases are probably removed rapidly as carrion or by predation.
Bats are drawn to turbines because their insect prey is enticed by the warmth emitted from the nacelles and consequently are caught up in the swirling blades and down draught they create. The low frequency noise created by the turbines also appears to interfere with their echolocation techniques.
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