Environmental Engineering Reference
In-Depth Information
Initially surveys were designed to detect all birds and bats (small and large
species) which had collided with turbines at these wind farms. However, after a
review of surveys and other management actions in 2010 (see Sims et al.
this volume
),
collision monitoring was focused on eagles and the methods were adapted for
detecting these species.
Survey frequency and coverage evolved over time (see Hull et al.
2013
; Hydro
Tasmania
2013
, and Annual Environment Performance Reports). Observers
searched out to approximately 100 m radius of turbines (which is consistent with
Hull and Muir
2010
). Search frequency was informed by scavenger and detectabil-
ity trials performed prior to the commencement of surveys. Since 2007, searches
have been conducted twice a week during what were assumed to be high risk peri-
ods (eagle display period 1 June-31 August and eagle fl edging period 15 December-1
March) and fortnightly outside these periods. The number of turbines surveyed also
varied, with all turbines monitored since 2007.
Formal surveys were supplemented by “drive-bys” (driving past each turbine to
check for eagles or carcasses, on a minimum of fortnightly basis) and ad hoc moni-
toring (where all staff and visitors to the wind farms were required to report any
bird or bat mortalities or injured birds or bats). All eagles found alive or dead on
site and featherspots (a collection of at least three primaries, secondaries or retrices
or ten of any other feathers) were documented and then removed. Injured eagles
were treated by veterinary practitioners approved by the State Regulator. All colli-
sions were reported to the regulators, as detailed in the relevant environmental
management plans.
The age of eagles was determined from plumage patterns (Marchant and Higgins
1993
) and sex was determined from post-mortem analysis, morphometrics (per
Marchant and Higgins
1993
) and/or genetic analysis (see Hydro Tasmania
2012
).
Statistical Analyses
Eagle collision data were examined for evidence of inter-annual variability, seasonal
or other temporal patterns. It was not possible to analyse spatial effects in these data
because there was a high level of uncertainty around which turbines were respon-
sible for some collisions (resulting in too few samples to analyse) and because of
incomplete data on survey effort at each of the turbines (particularly from ad hoc
monitoring). Therefore, nothing can be inferred about whether some turbines were
responsible for more collisions than others.
Small sample sizes precluded assessment of patterns in the sex and age of eagles
that collided. However, it should be noted that both adults and young eagles (juve-
nile or immature), and females and males have collided with turbines (see
Appendix
).
Due to the small number (three) of WBSE collisions at BPWF and no collisions
at the SBWF, it was not feasible to conduct statistical analyses of the WBSE data.
Therefore, all collision results presented pertain to WTE.
While it cannot be ruled out that some eagles may have been missed during the
monitoring, available evidence indicates that the detected mortalities are a reasonable
representation of what has occurred on these sites (Hydro Tasmania
2013
).
