Bird collision risks guidance

The behaviour of birds in proximity to wind turbines is still not well understood though monitoring information on bird behaviour and collisions is gradually becoming available for some species.

For collision risk, we recommend:

• assessing the theoretical number of collisions which would occur if birds take no avoiding action (this depends on levels of flight activity, the size and speed of the bird, and the dimensions and rotational speed of the turbine);
• applying an avoidance factor to reflect that, in practice, birds often succeed in avoiding a turbine blade, either by changing their route, measuring the timing of their flight through the rotor or by taking emergency avoidance action.

We have developed guidance on assessing collision risk  and on calculating the probability of collision  risk.

The Scottish Natural Heritage Collision Risk Model (CRM), at times known as the Band Model, provides a means of estimating collision risks and hence the potential bird mortality which may be caused by a wind farm. The CRM first estimates the number of collisions that would occur if the birds were to take no avoidance action (guidance above). It then applies an avoidance rate to take account of the likely degree of successful avoidance. The Use of Avoidance Rates  guidance describes that process.