Environmental Engineering Reference
In-Depth Information
Table 1
A summary of the species of internal migratory shorebirds recorded as migrating along
the Waikato coastline, their threat status, the estimated population size and the number potentially
passing through or past the proposed HMR wind farm
Population
estimate (DoC)
Number Estimated near
or through HMR (DoC)
Threat status
SIPO
At Risk, declining
111,085
70,000
Wrybill
Threatened, nationally
vulnerable
5,274
5,000
Pied stilt
At Risk, declining
30,000
9,000-13,000 (resident
and migratory)
Banded dotterel
Threatened, nationally
vulnerable
20,000
6,000
through the centre of each cluster and regarded as the cluster baseline. In order to
account for missed portions of flight paths, both ends of each radar trail were
extended on to the next cluster baseline on the assumption made by the shorebird
experts that most birds would continue on more or less the same line past the end
of the recorded flight path.
One of the more discussed input requirements was determining the proportion of
birds passing the site and passing through the site at the locality of the proposed
turbines. The likely population size of each species and the likely number of these
that would pass through or adjacent to HMR was estimated by the Expert Shorebird
Group. The Ornithological Society of New Zealand undertakes annual surveys of
birds at most harbours and roost sites throughout the country every winter and sum-
mer. These were used as estimations of likely numbers of birds in the vicinity of
HMR, but they are dependent on a number of assumptions, and consensus on an
ecologically reasonable, yet risk-conservative estimate can often be difficult. In this
case the Expert Shorebird Group accepted the larger population estimate proposed
by the DoC experts (Table
1
) so as not to underestimate likely collision mortality.
As not all of the birds fly as far north as the proposed wind farm, the proportion of
birds recorded as overwintering in harbours south of the site were eliminated from
the population size passing near the site. Also younger pre-breeding age birds
remain on northern harbours throughout the year and so do not migrate past the site
either and are eliminated from the likely population size passing the site.
Agreement was reached on the number of each migratory species, the percentage
of birds flying at rotor height, the percentage downtime, and the collision risk factor.
Agreement was also reached on the percentage of birds crossing each turbine
cluster.
The remaining input that required consensus was the 'avoidance rate' - the pro-
portion of birds that, even though they are flying in the rotor swept area, avoid the
blades. This proportion has the single largest effect on the mortality prediction
(Chamberlain et al.
2006
; Band et al.
2007
). The experts did not agree on the avoid-
ance rate distributions, with DoC's experts supporting much lower avoidance rate
than the SNH rates and those advocated by the Contact Wind and Council-appointed
