Draft National Wind Farm Development Guidelines - July 2010

that it was first observed. Where more than one individual is seen simultaneously each bird
provides a separate flight record.
A utilisation rate should incorporate the amount of available flight time per annum for key
species. This must account for variables of seasonal, diurnal/nocturnal and tidal cycles that
may affect presence at the site and patterns of bird activity. In addition to truly nocturnal
birds, many diurnal birds also fly during the hours of darkness.
Visual counting by trained ornithological observers is the usual method employed for point
count surveys of birds. Similar techniques may be applicable to visual counting of
crepuscular flights of fruit bats and cave-dwelling bats as they fly from colony locations.
However this method is not applicable to documenting truly nocturnal activities of birds or
bats. It is also limited during daylight when weather conditions reduce visibility, and even
due to observers’ capacity to detect birds over distance. Vertical and horizontal marine
surveillance radar have been used to document diurnal and nocturnal birds and bat
movements at some overseas wind farm sites (Johnson and Strickland 2003, 2004;
EchoTrack 2005) and has potential for this application in Australia. Data from radar does
not readily permit identification of species and generally requires calibration against
simultaneous visual observation of birds during daylight hours, monitoring of the calls of
nocturnal birds and use of acoustic bat detectors as means to identify species in flight.
Representative sampling of bird and bat utilisation should encompass all variations that
occur in the course of a year.
Flight height
Flight-height data for birds collected in the course of wind farm assessments in southeastern
Australia indicates that many bird taxa rarely fly within rotor-swept height and that
interactions with turbines by such taxa are thus unlikely (Biosis Research unpublished data).
For these taxa assessment for collision risk will not be required other than for exceptional
sites or circumstances. Liaison with relevant authorities should be undertaken to determine
taxa that may not require assessment for a particular location.
Data requiring heights of bird flights may require calibrated estimation of heights. More
precise data for height above the ground may be obtained from vertical radar. Longrange
thermal imaging and some range-finding technologies offer capacity to record
distance from observer to a bird or bat and may allow height above ground to be derived
from data records. However, such technologies are not without limitations which should be
evaluated in determining whether they are applicable to a particular wind farm site. The
cost and precision of such methods may also not be warranted in all situations. Flight
heights or height estimates should be recorded rather than simple allocation of flight
records to ‘below-‘, ‘within-, ‘above rotor-swept zone’. This permits data to be used for
analysis regardless of any changes to turbine dimensions that might occur during planning
of the wind farm.
Site population census
Collision risk modelling may require a census or estimation of the annual maximum
numbers of individuals of key species that could encounter and interact with the turbine
array. For birds, this may be obtained from appropriately designed simultaneous counts
designed to document the complement of birds present across the site. Any available
historical records of maximum numbers should also be taken into account. There is a
substantial literature on bird census techniques and Bibby et al. (2000) provides a good
introductory overview.
Collision risk modelling
Quantified collision risk modelling is a predictive mechanism used to project the annual
number of flights made by key species that are at risk of collision and may thus result in
fatalities. Inputs required to undertake such modelling include standardised bird utilisation
data; number and geographic layout of turbines; and dimensions and other parameters of
turbines. Pre-requisites for an outcome measured in terms of an expected annual number
Page 138 Draft National Wind Farm Development Guidelines – 2 July 2010