Environmental Engineering Reference
In-Depth Information
species show that many rarely fly at the height of turbine rotors in open environments
where turbines are generally sited. Clearly these species are at less of a risk of col-
lision than species that routinely fly at rotor height.
However, predominant flight-height is not the sole factor contributing to colli-
sion risk. When we have compared flight height data collected for multiple species
byBiosisatnumeroussiteswithresultsofcollisionfatalitydata,itisapparentthat
many species that regularly fly within rotor-swept height are rarely involved in col-
lisions and some are not at all. This requires further study, but there are likely to be
a range of factors involved. For instance the very reason that birds fly is highly vari-
able. Some taxa fly infrequently and use flight to simply move from one place to
another while others spend the majority of their waking hours in the air hunting,
feeding,displayingandcarryingoutahostofotherbehaviours.Mostspecieshave
evolved in the absence of large obstacles within the airspace they use. The visual
realms in which birds function vary enormously and visual acuity, allowing birds to
avoid collisions, also differs widely between taxa (Martin
2011
). Some taxa may
also have a greater capacity than others to judge turbines as presenting a potential
risk.
Overseas and in Australia, assessments of wind farm collisions continue to
emphasise collisions by large species, especially large raptors. For threatened raptor
species, assessment of risk is clearly relevant. However, there may also be an anthro-
pogenic transfer of concern for large species even if they are not threatened or not
at great risk. For instance the wedge-tailed eagle continues to be given high consid-
eration for many mainland Australian wind farms despite the species being quite
secureandnotofanyconservationconcern.Publicsubmissionstowindfarmplan-
ning approvals processes in which I have been involved indicate that this is princi-
pally due to perceptions of it as a charismatic bird. Limited information about
mortalities detected at mainland south-eastern Australian wind farms indicate that
Australian magpie, small raptors including nankeen kestrel and brown falcon, and
white-striped freetail bat are subject to substantially greater numbers of collisions
thanotherspecies.Butinmyexperience,thesespecieshaveneverbeengivencon-
sideration in a wind farm approval process. All of them are considered to be secure
and the abundance of some of them is likely to have increased in response to
European modification of rural landscapes. Taxonomic and ecological characteris-
tics of taxa that collided and did not collide with turbines at Tasmanian winds farms
are evaluated in Hull et al. (
2013b
), which found some specific patterns.
Frequency of Collisions
To determine the frequency of collision, it is usually necessary to extrapolate the
results from monitored turbines to all turbines at a wind farm. It is also necessary to
account for numbers of carcasses that are removed by scavengers or missed during
searches due to variability in their detectability. These influences all appear to be
specific to individual wind farms.