Buteo buteo (Linnaeus, 1758)

3 BUZZARD ( BUTEO BUTEO View in CoL )

The overall buzzard flight activity was 3.27 x 10-7hrs/ha/hr, amounting to 1.28 x 10-3 hr/hr over the whole site.

Buzzards were present on the site throughout the observation period, amounting to 153 days and they were presumed to be able to fly for an average of 14.1 hours daylight per day, a total of 2157.3 hours

Buzzard occupancy ( n) of the wind farm area is, therefore, estimated to be 2.76 hours per year for the observation period (1.28 x 10 -3 x 2157.3).

3.1. 2 Number of Transits of Buzzard Through the Rotors

The size of the flight risk volume (Vw) is 4,682,040,000m 3. The combined volume swept out by the turbine rotors (Vr) is 1,533,516.87m 3 using a body length for buzzard of 0.54m.

The bird occupancy of the volume swept by the rotors in seconds ( b) is:

( n x 3,600) x (Vr/Vw)

= ( 2.76 x 3600) x (1,533,516.87/4,682,040,000)

= 3.25 bird-secs.

The time taken for a bird to make transit through the rotor and completely clear the rotors ( t) is (d + l)/v, where d is the depth of the rotor blade from front to back (4), l is the body length for buzzartd (0.54m) and v is the speed of the bird through the rotor (11 ms-1) (33), = 0.41secs.

The number of bird transits through the rotors per season is b / t = 7.87

3.1. 3 Estimating Collision Likelihood

Using the SNH spreadsheet, and assuming a buzzard flight speed of 11 m/s, the model predicts that an average of 20.5% of buzzard flights through the rotor swept area would result in collisions. This was reduced to 16.4% to allow for non operating time.

The number of birds predicted to collide with the operating rotors over the season is 1.29 birds per year (7.87 x 16.4%). This assumes no avoiding action is taken by the birds.

Avoidance rates were calculated as for kestrel. Mortalities were calculated using avoidance rates of 90%, 95%, 98% and 99% to provide an indication of potential risk (see Table 1.4 below).

This equates to a loss of a bird every 15.48 years during the observation period at 95% avoidance or a bird every 77.44 years at 99% avoidance.