Draft National Wind Farm Development Guidelines - July 2010

wind farms. Such data from existing wind farms may inform the ongoing evolution of
collision risk modelling and facilitate the “calibration” of a collision risk model for particular
species in order to provide greater confidence in its predictions.
Various sources of uncertainty are necessarily inherent in risk modelling and these should
be explicitly stated in reporting of the process. Wherever feasible, statistical confidence
levels should be provided for results of modelling.
Some fundamental parameters are necessary for measuring the activity of birds or bats
that contribute to their annual risk of collisions. In combination, these are termed ‘bird, or
bat, utilisation’ for the site. Studies should be undertaken to obtain empirical utilisation data
from the site for key species according to standard metrics. Standard measures allow
utilisation rates to be compared between sites and to be combined for the purposes of
assessing cumulative impacts of multiple wind farms.
Standard metrics that contribute to measures of utilisation for particular species and sites
include the following:
• Census or estimation of the annual maximum numbers of individuals of key species
that could encounter and interact with the turbine array.
• Estimated annual number of flights at risk of collision made by key species. This should
be extrapolated from surveys designed to document numbers of flights made within
rotor-swept-height per unit time and space.
• Amount of available flight time per annum for key species. This must account for
annual and diurnal/nocturnal cycles that affect presence at the site and/or
frequency of flights.
Field studies should be undertaken to a design regime that will obtain empirical information
about these aspects for the site.
For scarce bird species, for migratory species that may move through a site during a brief
episode or for microchiropteran bats it may not be feasible or practicable to obtain
empirical, or statistically valid, data for all of these parameters. In such cases a
precautionary approach based on a set of informed assumptions should be adopted. It
should use confirmed information available for the taxon and/or closely related taxa. All
assumptions to be used and uncertainties inherent in the process should be agreed by the
relevant authorities and reviewed by experts on the taxon in question. They should also be
explicitly stated in reporting the assessment process.
Results of collision risk modelling provide projections of bird or bat mortalities that can be
used as inputs to the subsequent evaluation of impacts on populations of key species.
Evaluation of predicted inherent impacts on populations of key species
Principal question:
Purpose:
Methods:
Is the forecast impact of the proposed wind farm ecologically important
To determine if the potential risk of loss identified in the previous phase is
significant to the population in question.
For this stage, the studies will include:
• Population Viability Analysis (PVA)
• Potential Biological Removal assessments (PBR)
Evaluation of predicted mortalities of key species due to the wind farm should be based
on the degree to which they might affect maintenance and functioning of the species’
population. ‘Acceptability’ or otherwise of impacts is thus based on the species’ ecology
and not on a simple number of mortalities that may occur.
Page 126 Draft National Wind Farm Development Guidelines – 2 July 2010