Data from: Three dimensional tracking of a wide-ranging marine predator: flight heights and vulnerability to offshore wind farms

A large increase in offshore wind turbine capacity is anticipated within
the next decade, raising concerns about possible adverse impacts on birds
as a result of collision risk. Birds’ flight heights greatly influence
this risk, yet height estimates are currently available only using methods
such as radar- or ship-based observations over limited areas. Bird-borne
data-loggers have the potential to provide improved estimates of collision
risk and here, we used data from Global Position System (GPS)-loggers and
barometric pressure loggers to track the three-dimensional movements of
northern gannets rearing chicks at a large colony in south-east Scotland
(Bass Rock), located <50 km from several major wind farm
developments with recent planning consent. We estimated the foraging
ranges and densities of birds at sea, their flight heights during
different activities and the spatial variation in height during trips. We
then used these data in collision-risk models to explore how the use of
different methods to determine flight height affects the predicted risk of
birds colliding with turbines. Gannets foraged in and around planned wind
farm sites. The probability of flying at collision-risk height was low
during commuting between colonies and foraging areas (median height 12 m)
but was greater during periods of active foraging (median height 27 m),
and we estimated that ˜1500 breeding adults from Bass Rock could be killed
by collision with wind turbines at two planned sites in the Firth of Forth
region each year. This is up to 12 times greater than the potential
mortality predicted using other available flight-height estimates.
Synthesis and applications: The use of conventional flight-height
estimation techniques resulted in large underestimates of the numbers of
birds at risk of colliding with wind turbines. Hence, we recommend using
GPS and barometric tracking to derive activity-specific and spatially
explicit flight heights and collision risks. Our predictions of potential
mortality approached levels at which long-term population viability could
be threatened, highlighting a need for further data to refine estimates of
collision risks and sustainable mortality thresholds. We also advocate
raising the minimum permitted clearance of turbine blades at sites with
high potential collision risk from 22 to 30 m above sea level.