Environmental Engineering Reference
In-Depth Information
experts. Consequently, the parties do not agree on the final mortality rates. The
Expert Shorebird Group in their April 2010 Caucus Statement noted that:
Determining suitable avoidance rates for use at HMR has been the most challenging issue
for the group, mainly because of:
(a) The fact that results from collision risk models are so highly sensitive to changes in
avoidance rates;
(b) A paucity of empirical data on avoidance rates of shorebirds globally;
(c) The lack of empirical data on avoidance rates of New Zealand birds (including shore-
birds), and
(d) The difficulty in determining the applicability of overseas data to the New Zealand
situation.
As a result, the opinions of different experts as to what constitute appropriate rates have
evolved during the caucusing process, particularly as new information came to hand. The
group has now reached a position where it is agreed that the differences of opinion on this
issue will not be resolved. It therefore presents a range of values for predicted collision
mortality reflecting the different avoidance rates adopted.
DoC representatives made mention of special features of New Zealand birds that
arguably made the birds more susceptible to collision and supported these with
anecdotal evidence when arguing for a lower avoidance rate. These special features
include the minimal predator avoidance behaviour of New Zealand birds in relation
to all but bird predators, the recording of some birds flying into fences and collisions
with planes at airports. They argued further that because a majority of winter flights
were in darkness avoidance should be lower. In contrast, the applicant chose to
adopt a conservative range based on the published data from international studies as
embodied in the SNH published figures (
www.snh.org.uk
)
. This for waders is set at
a minimum of 98 %.
In order to provide variance around the output, the avoidance rate was set as a
Beta distribution with the Contact Wind and DoC expert teams opting for different
likely distributions. The representative from the consenting authorities opted for
numbers similar to those recommended by the Contact Wind experts. The DoC
experts opted for more conservative figures. The migrant population passing through
or adjacent to HMR was set to vary by up to 10,000 birds. The flying heights of
flocks varied and records showed their maximum and minimum heights. This was
bootstrapped to give a distribution of likelihood of flying at RSH.
All parties agreed to the same distributions of all variables except for avoidance
rates. Contact Wind experts set avoidance of both species to lie between 95 and
99.9 % with a mode of 98 %. In contrast, DoC experts argued for 95-99 % with a
mode of 97.5 % for SIPO in summer but 90-97.5 % with a mode of 95 % in winter.
For Wrybill DoC experts argued for a summer avoidance between 92 and 97 % with
a mode of 95 % and in winter 91-95 % with a mode of 92.5 %. There was general
agreement that all figures chosen were more likely to overestimate collision mortal-
ity than underestimate it. The resulting predicted mortalities for the three groups are
given in Table
2
.
