Forthbank Wind Energy Development - Partnerships for Renewables

Forthbank Wind Energy Development
enclosed by the 4 turbines) it is unlikely that birds will have to make large detours in order to
avoid the development and so no increase in energy expenditure is expected 33 .
12.4.17 Furthermore, although some birds may avoid flying through the operational wind energy
development, given the configuration of the four turbines (i.e. a cluster of three to the south
east of the site and a single isolated turbine located approximately 800m to the north east, see
Figure 1.1 (Site Location Plan) and Figure 1.2 (Site Layout)), it is likely that many will still be
able to commute safely between the Forth Estuary and adjacent habitats through this corridor.
Even assuming an avoidance distance of 100m from the nearest turbines this would still leave
a corridor of over 500m.
12.4.18 Consequently, it is considered that the proposed wind energy development is unlikely to
present a significant barrier to the movement of birds in the vicinity of the wind energy
development.
Collision
12.4.19 Collision of a bird with the turbine rotors is almost certain to result in the death of the bird. The
impact of an individual loss on a population is influenced by several characteristics of the
affected population, notably its size, density, recruitment rate (additions to the population
through reproduction and immigration) and mortality rate (the natural rate of losses due to
death and emigration).
12.4.20 In general, the impact of an individual lost from the population will be greater for species that
occur at low density, are relatively long-lived and reproduce at a low rate. Such species
include wildfowl and the larger raptors. Conversely, the impact will often be insignificant for
short-lived species with high reproductive rates found at high densities, including most
passerines (e.g. skylark).
12.4.21 In broad terms, the number of collisions during a given period (e.g. a year) is the product of 2
factors:
• The number of birds flying through the rotors during the period (the number of rotor
transits). The number of rotor transits is influenced by the frequency with which a
species flies through the wind farm area and, crucially, the probability that any bird
on a collision course will take avoiding action (the avoidance rate); and
• The probability that a bird will be struck by the rotors on any given transit. The
probability of collision for a bird passing through the rotors is mainly determined by
the size of the bird, its mode of flight (flapping or gliding) and its flight speed, along
with the dimensions of the rotors and the speed at which they rotate.
12.4.22 Collision risk is perceived to be higher in birds that spend much of the time in the air, such as
foraging raptors and those that have regular flight paths between feeding and
breeding/roosting grounds (e.g. divers and geese). Vulnerability to collision is also influenced
by factors such as the flight manoeuvrability of a species and its tendency to fly in conditions of
reduced visibility (e.g. at night or in fog).
November 2010 Chapter 12 Page 40
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