Windfarms may impact on ornithological interests in a number of ways. There may be:
- loss of habitat, due to the construction of turbine bases and tracks
- displacement of birds as a result of disturbance
- potential mortality through collision.
SNH Guidance note describes a methodology for assessing in full the impact of windfarms on ornithological interests, taking account of each of these effects. The methodology includes a two-stage process for the assessment of collision risk. More detailed prescriptions for use in the second stage of that collision risk assessment are set out here. It sets out how to estimate a 'no-avoidance risk', i.e. the rate of collision assuming that birds fly as if the wind turbine structures and rotors were not there and take no avoiding action whatsoever. It is assumed that if a bird is hit it is killed, whether immediately or through injury.