This series focuses on the methods used and results generated by collision risk modelling for pink-footed geese in the greater Wash.
It is possible to estimate mortality rates of birds passing through a wind farm given key
parameters of the placement, dimension and operation of the wind turbines and the
movements, abundance and behaviour of the birds. This has lead to the development of
collision risk models.
For an offshore site, the data to estimate the abundance (and movements) of the birds
should preferably come from boat-based surveys. In the boat-based surveys ‘snapshots’
are used to quantitatively assess flying birds. Snapshots are predefined moments during
the survey at which all flying birds within a certain distance from the surveyor are recorded.
From the snapshot data one can calculate the density of birds in flight (e.g. number
of flying birds per square km).
However, with Pink-footed geese (PG) there is a (potential) problem with this methodology.
This is due to the fact that very few PG have been recorded in snapshots. In the 19
boat-based surveys for the offshore wind farms Lynn and Inner Dowsing (LID), only 5
PG were recorded in snapshots during a single survey in November 2003. Similar results
were found in the boat-based surveys for the Lincs offshore wind farm: 54 PG in a single
survey in September 2004, out of 33 boat-based surveys. During the boat-based surveys
for Docking Shoal OWF not a single PG was recorded in snapshots in any of the 39 surveys.
The statistical validity of collision risk modelling based on the incidental records of
Pink-footed geese in or near LID or Lincs is therefore questionable at best.
There is an alternative approach. The Pink-footed geese pass through the Greater Wash
during the migration to and from their overwintering ground in Norfolk. A reasonable estimate
of the annual passage rate of PG through a wind farm site can be made on the basis
of the maximum number of PG recorded overwintering in Norfolk, and some reasonable
assumptions on the flight corridor along the Lincolnshire Coast. The maximum number of
PG yet recorded in Norfolk is 152,514 ind. (recorded on 13th December 2004 - Norfolk
and Norwich Naturalists’ Society 2005).
In this report the results from both approaches are presented. It was found that compared to the mortality rates calculated based on the site specific boat-based surveys, the calculated total mortality rate based on the maximum regional population is about a factor of two higher.