Environmental Engineering Reference
In-Depth Information
activity, but a constant rate of success for nests that were active. The onsite WBSE
nest (823, only surveyed pre-2007) appeared to be active more regularly and typi-
cally successful, than those from elsewhere, with no evidence that breeding success
was different in the years it was surveyed. There was no indication of negative
trends, other than the potential decline in the WBSE activity overall.
Display Period and Post-collision Eagle Observations
A total of 838 days (BPWF 408 days; SBWF 430 days) of dawn to dusk eagle
observations were conducted. The observations documented 1,731 fl ights of WTE
and 941 fl ights of WBSE at BPWF, and 1,583 WTE and 325 WBSE fl ights at
SBWF (for further details see Hull and Muir
2013
). Unfortunately, post-collision
observations did not provide insights into why eagles collided with turbines, and
the design of the display period observations did not allow an assessment of
whether there were any seasonal changes in the behaviour of eagles. However, the
observational data set allowed the avoidance rates of eagles at these sites to be
calculated using a new approach (detailed in Hull and Muir
2013
). Both species
exhibited a distinct avoidance of the turbines, and demonstrated a preference for
fl ying between turbines.
Avoidance rates were 81-97 % and differed signifi cantly between the species
and sites, with WBSE avoiding at a higher rate than WTE, and eagles at BPWF hav-
ing higher avoidance rates than those at SBWF. Both species altered their avoidance
rate with stage in the wind farm development, but only WTE showed a change in
avoidance rates with weather conditions, demonstrating higher avoidance rates dur-
ing wet and windy conditions. No change in avoidance rates occurred when more
than one eagle was in the sky at a time (for full results see Hull and Muir
2013
).
Discussion
The interaction between birds and wind farms often focusses on raptors and there
are probably a range of reasons for this. While some species are listed as threatened,
and concerns are raised around them being long-lived and they often exist at low
densities relative to many other taxa, much of the focus also may be related to a
signifi cant community interest in the group (Madders and Whitfi eld
2006
). The
group is generally thought to be at risk of collisions with turbines, although recent
analysis has found that collision risk varies between raptor species, and that at some
sites, other species of bird are more prevalent in collision records than raptors (Hull
et al.
2013
).
WTE and WBSE have continued to use the BPWF and SBWF since construction
of the facilities and throughout their operation, Furthermore, a new WBSE was
established at the BPWF in 2005 after the wind farm became fully operational.
