Environmental Engineering Reference
In-Depth Information
There is no evidence to suggest that individuals suffer disturbance effects such as
alienation (where a wind farm or group of turbines result in birds no longer using
the area, see Langston and Pullan
2003
) at these sites.
A number of studies at overseas wind farms have also found that raptors continued
to use operational wind farm sites (see for example, Smallwood and Thelander
2004
; Madders and Whitfi eld
2006
; Nygård et al.
2010
), although one study docu-
mented reductions in use (Garvin et al.
2011
). Walker et al. (
2005
) found that resi-
dent golden eagles
A. chrysaetos
avoided a wind farm in Scotland following its
construction, but it is likely that this was due to the clearing of a large area of planta-
tion forestry nearby, conducted with the intent of providing new foraging habitat for
the eagles away from the wind farm (Walker et al.
2005
).
While there was no evidence of eagles being alienated from the BPWF and SBWF,
there was a documented change in how they used the sites in comparison with a
greenfi eld site (Hull and Muir
2013
). Eagles actively avoided the immediate vicini-
ties of turbines showing a preference for fl ying at an equal distance between them.
Combined totals of 18 WTE and three WBSE collisions have been recorded at
these wind farms, equating to average annual collision rates of 0.95 and 1.54 WTE
and 0 and 0.36 WBSE per year (Table
1
). The data suggest that WBSE are at less
risk of collision than WTE at these sites, which may refl ect species-specifi c behav-
ioural or ecological differences (Hull and Muir
2013
). However, anecdotal observa-
tions have prompted the suggestion that WTE may suppress the movements and
behaviour of WBSE, contributing to reduced collision risk for WBSE. This hypoth-
esized behavioural suppression requires further investigation. This information
could be relevant to sites where only WBSE occur.
The collision rates of WTE are within expectations of collision risk modelling
for a range of avoidance rates using the Biosis collision risk model (see Smales et al.
2013
), but the collision rate of WBSE is lower than that estimated by the modelling
(Hydro Tasmania
2013
; Smales et al.
2013
). The documented collision rates of both
species are also below the maximum estimated collision rates in the analysis con-
ducted (see Hydro Tasmania
2000
) and upon which the wind farms were approved
and offsets for potential mortalities determined.
The collision rate at the BPWF and SBWF was found to be constant over time,
with no statistical evidence for any year being signifi cantly different to any other.
Instead, the pattern of collisions at these sites is well described by a simple random
(Poisson) distribution. This fi nding includes the multiple mortalities attributed to
2006, which the testing suggests were within the limits of random variation.
There is some indication of a decreasing collision rate of WTE at SBWF as three
of the fi ve mortalities occurred in the fi rst year of operation. However, the statistical
test used to evaluate this is unreliable for values of around three or less. Although
there were only fi ve detected mortalities of this species overall at SBWF, this test
has a bias towards falsely fi nding a trend and hence caution should be used in inter-
preting this result.
The collision data were rigorously tested to determine whether there was evi-
dence of seasonal effects or other clustering patterns. None was found. Clustering
