Publication - Progress report

Scottish Marine and Freshwater Science Volume 5 Number 16:The Avoidance Rates of Collision Between Birds and Offshore Turbines

Published: 3 Dec 2014
Part of:
Marine and fisheries
ISBN:
9781784129125

This study reviewed data that have been collected from offshore windfarms and considers how they can be used to derive appropriate avoidance rates for use in the offshore environment.

Scottish Marine and Freshwater Science Volume 5 Number 16:The Avoidance Rates of Collision Between Birds and Offshore Turbines
Appendix 5 Evidence review micro-avoidance

Appendix 5 Evidence review micro-avoidance

A5.1 Egmond aan Zee

Krijgsveld, K.L., Fijn, R.C., Japink, M., van Horssen, P.W., Heunks, C., Collier, M.P., Poot, M.J.M., Beuker, D., Dirksen, S. 2011. Effect studies offshore wind farm Egmond aan Zee. Final report on fluxes, flight altitudes and behaviour of flying birds. Bureau Waardenburg

Methods

Between July and December 2009, the flight paths of birds around six turbines were observed visually. These flight paths were then related to short range radar tracks in order to estimate the altitude and distance to nearest turbine. As a result, a dataset containing high resolution observations of bird behaviour around turbines was created. Birds were assigned to 5 m horizontal distance bands beginning at the rotor hub. All birds flying between 20 and 120 m above sea-level (reflecting the rotor-swept area of each turbine) were considered to be at risk of collision and the number of birds within each 5 m band was compared to the number of birds that would have been expected if they had been distributed evenly. To assess the level of last-second avoidance action taken, the number of birds within the 45-50 m band (just outside the rotor-sweep) was compared to the number of birds recorded between 0 and 45 m from the rotor hub.

Seasons / time of day

Data were collected during daylight on eight occasions between July and December.

Species

Seabirds, waterbirds and other migrants.

Conditions data collected under

All conditions.

Location / habitat

Marine, 10 km offshore.

Turbine / array specification

Egmond aan Zee Offshore Windfarm covers an area of 27 km 2 and contains 36 turbines. Each turbine has a hub height of 70 m and rotor diameters of 90 m. Turbines are arranged in four rows, with 650 m between turbines in each row and 1 km between rows. The study of micro-avoidance covered six turbines at the edge of the windfarm.

Results

Whilst 1,610 birds in 409 groups were recorded over the course of the study, only 115 in 52 groups were recorded passing within 50 m of the turbines. Of these, only 36 birds were recorded between 20 and 120 m, at heights placing them at risk of collision. Of the 36 birds passing within 50 m of the turbine and at rotor height, it is reported that 0.926 did not fly within the rotor swept window of the turbine ( i.e. 2-3 birds). This would reflect a micro-avoidance rate of 0.926.

Assessment of methodology

The described methodology of combining visual and radar observations to record the tracks of birds approaching turbines is robust. This makes it possible to relate tracks to individual species and to determine how close each individual, or flock, gets to a turbine. Focussing on the area 50 m either side of the rotor hub and comparing the proportion in the 45-50 m band to the proportion in the 0-45 m band data is likely to capture the type of last-minute action covered by micro-avoidance.

However, only limited weight can be given to the data presented here. Observations were recorded on only four days, during which only 36 birds were recorded passing within 50 m of the turbine, the distance presented to represent micro-avoidance. This figure may be substantially inflated as it includes a single observation of a flock of 28 skylark.

A5.2 Greater Gabbard

RPS. 2011. Galloper Wind farm Project Environmental Statement - Technical Appendices 2: Appendix 4: Greater Gabbard post-construction vantage point surveys, RPS, Glasgow

Methods

Visual Observations

Two surveyors collected data from 180˚ arcs to the port and starboard sides of a stationary vessel within Greater Gabbard Offshore Windfarm. Each arc had a radius of 2 km and all birds entering each arc were recorded during snapshot counts taken every 15 seconds. The location of the boat and the viewing area, which covered a total of 15.9 km 2, included seven operational turbines and a total of 36 hours of data were collected during the survey. The flight paths of each bird within the viewing area were noted, as was the proportion of time each bird spent at different heights.

Seasons / time of day

Data were collected between 1 st June 2011 and 28 th July 2011, with each survey lasting four hours.

Species

Northern gannet (0.14 birds/hr), Arctic skua (0.03 birds/hr), lesser black-backed gull (3.69 birds/hr), herring gull (0.11 birds/hr), black-legged kittiwake (1.28 birds/hr).

Conditions data collected under

Conditions were limited to sea-states one and two, to ensure the vessel remained as a stable observation platform.

Location / habitat

Greater Gabbard, UK (offshore).

Turbine / array specification

The survey monitored seven operational turbines, each with a hub height of 77.5 m and a rotor diameter of 107 m.

Results

Over the course of the study period, 190 flights through the area were recorded. Of these, the vast majority did not pass close to the turbines. Given the proportion of the total study area occupied by turbines, this is unsurprising. As a consequence, only a single evasive manoeuvre, involving a kittiwake, was recorded.

Assessment of methodology

The length of the observation periods carried out during this study were extremely limited, so it is difficult to make an accurate assessment of how widespread different avoidance actions are. In addition, records of avoidance action have been made in a subjective fashion, both in relation to assessing the number of birds on a collision course for the turbines, and in assessing the actions recorded. For these reasons, it is not possible to quantify the micro-avoidance behaviour reported in this study.

A5.3 Kessingland Windfarm

Wild Frontier Ecology. 2013. Kessingland Windfarm Annual Post-construction Monitoring Report Year 2. Wild Frontier Ecology, Norfolk

Methods

Bird activity was monitored within the windfarm through nine two-hour vantage point surveys at each turbine carried out between November 2012 and March 2013. In total 36 hours of survey effort was completed throughout the study period. The response of birds whose flight paths were likely to overlap with turbines was noted.

Seasons / time of day

Late morning - early afternoon during winter.

Species

Black-headed gull (97 birds/hr), common gull (31.4 birds/hr), lesser black-backed gull (11 birds/hr),

herring gull (56.72 birds/hr), great black-backed gull (0.28 birds/hr).

Conditions data collected under

No details given.

Location / habitat

Kessingland, Suffolk, UK (terrestrial).

Turbine / array specification

Two turbines with hub heights of 80 m and rotor diameters of 92 m. Distance between turbines within each row is not described.

Results

All birds recorded as being on a collision course with the turbines were observed to take evasive action to avoid collision. Typically this action occurred at a distance of 0-50 m from the turbine. Over the course of the study period, five black-headed gulls, two lesser black-backed gulls and a herring gull were recorded taking evasive action. In three instances this involved a change in altitude to fly below the rotor blades, whilst in other instances it involved a change to flight direction. In the case of the two lesser black-backed gulls, both were observed to take last minute evasive action at just five metres from the blades.

Assessment of methodology

The length of the observation periods carried out during this study were extremely limited, so it is difficult to make an accurate assessment of how widespread different avoidance actions are. In addition, records of avoidance action have been made in a subjective fashion, both in relation to assessing the number of birds on a collision course for the turbines, and in assessing the actions recorded and the distances at which they occur. For these reasons, it is not possible to quantify the micro-avoidance behaviour reported in this study.

A5.4 Nysted

Desholm, M. 2005. TADS investigations of avian collision risk at Nysted offshore wind farm, autumn 2004. NERI, Denmark

Petersen, I.K., Christensen, T.K., Kahlert, Desholm, M., Fox, A.D. 2006 Final results of bird studies at the offshore wind farms at Nysted and Horns Rev, Denmark, NERI, Denmark

Methods

Using a Thermal Animal Detection System (TADS) all bird movements past a single turbine during spring and autumn 2004 and spring and autumn 2005 were recorded. Birds were detected at distances of up to 120 m.

Seasons / time of day

Data were collected throughout both day and night in the spring and autumn.

Species

Mostly migrant passerines and waterbirds.

Conditions data collected under

All conditions.

Location / habitat

Located approximately 11 km offshore in the Danish part of the Baltic Sea.

Turbine / array specification

An array of 72 turbines arranged in eight rows of nine turbines each. Turbines have a hub height of 69 m and a rotor diameter of 92 m.

Results

In over 123 days of continuous monitoring, cameras captured 5,507 video sequences of which only 14 were found to include birds. Of these, none revealed birds passing close to the turbine.

Assessment of methodology

The methodology is robust with sufficient capability to record all birds passing the turbine over the study period. However, the low frequency with which birds were recorded passing close to the turbine suggests that the data are unlikely to have sufficient power to detect avoidance activity.


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