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 4 Evidence review vertical meso-response

Appendix 4 Evidence review vertical meso-response

A4.1 Barrow Offshore Windfarm

Barrow Offshore Wind Limited. Post Construction Ornithological Monitoring - Third Year Report and Overall Conclusions.

Methods

Boat-based estimation of flight heights.

Following the construction of Barrow Offshore windfarm, boat-based surveys were carried out during the breeding season and autumn migration in 2006, 2008, 2009 and 2010. In total 12 surveys, each lasting a single day were carried out, of which 8 were during the breeding season (May to August) and 4 during autumn migration (September to November). Boat survey data were collected within the windfarm according to standard protocols (Camphuysen et al. 2004) and flying birds were assigned to height bands of <5 m, 5- 15 m, 15-100 m and >100 m. Birds at risk of collision were assumed to be all those flying >15 m. The proportion of birds observed flying at heights presenting a risk of collision were then summarised across all surveys. Pre-construction proportions at collision risk height within the windfarm were compared to post-construction proportions at collision risk height, although no detailed analyses were undertaken.

Seasons / time of day

Data were collected during the breeding season and autumn migration periods.

Species

Auk spp. (238 recorded in 2010), common guillemot (2,002 recorded in 2010), razorbill (691 recorded in 2010), great cormorant (5 recorded in 2010), red-throated diver (2 recorded in 2010), black-headed gull (6 recorded in 2010), common gull (5 recorded in 2010), great black-backed gull (23 recorded in 2010), herring gull (142 recorded in 2010), black-legged kittiwake (132 recorded in 2010), lesser black-backed gull (425 recorded in 2010), gull spp. (51 recorded in 2010), Arctic skua (2 recorded in 2010), northern gannet (53 recorded in 2010), Manx shearwater (12 recorded in 2010), Sandwich tern (30 recorded in 2010), common scoter (10 recorded in 2010),

Conditions data collected under

No details given.

Location / habitat

Marine 7 km Offshore

Turbine / array specification

An array of 30 turbines covering an area of 10 km 2 and arranged in four rows of seven or eight turbines each. The rows are separated by a distance of 750 m and within the rows, each turbine is separated by a distance of 500 m. Each turbine has a hub height of 75 m above sea-level and a rotor diameter of 90 m.

Results

Several species were not present in sufficient numbers to allow a reliable estimate of the changing proportion of birds flying at a height placing them at risk of collision. Of those that were, common guillemot, great black-backed gull, herring gull, lesser black-backed gull and Sandwich tern all showed a decline in the proportion of birds flying at risk height, with meso-responses of 1, 0.29, 0.65, 0.28 and 0.55 respectively. However, other species (or groups) showed an increase in the proportion of birds flying at risk height including black-legged kittiwake, unidentified gulls and northern gannet, with meso-responses of -0.41, -0.85 and -0.59 respectively, reflecting an apparent attraction to the rotor-swept area of the turbines.

Assessment of methodology

Boat-based data collection was robust, following standard methodologies (Camphuysen et al. 2004). However, in assessing the vertical response to turbines there is a key flaw in the available data. In order to compare flight height data to that collected pre-construction, the same flight height bands were used in both study periods, and it was assumed that all birds flying at a height of more than 15 m above sea-level were potentially at risk of collision. However, as the rotor-swept area covers an area from 30 m to 120 m above sea-level, this may lead to a significant over-estimate of the actual number of birds flying at collision risk height. As a result, the meso-response rates of birds within the windfarm may be underestimated. An additional, arguably less serious, flaw in the data collection is that estimates of the birds at collision risk height refer to flocks, rather than individuals. Flock size is likely to show significant variation, making it difficult to infer what the proportional changes mean in relation to actual numbers of birds.

A4.2 Blyth Offshore Windfarm

Rothery, P., Newton, I., Little B. (2009) Observations of seabirds at offshore wind turbines near Blyth in northeast England. Bird Study 56, 1-14

Methods

Shore based observations were undertaken between 18 April 1998 and 30 August 2003 covering the pre-construction, construction and post-construction periods of Blyth Offshore Windfarm. Observations were carried out at pre-determined times, at least twice a month. All passing birds were recorded, and it was stated that all birds were visible at a range of 1 km, although the turbines are only likely to comprise a small part of the total observation area. All birds were assigned to one of four height categories - 0-9.1 m, 9.1-26.4 m, 26.4-92.4 m and >92.4 m. A total of 70.3 hours of monitoring were available for the pre-construction period and 351.6 hours for the post-construction period, although no analyses were undertaken to assess the significance of any changes in flight height.

Seasons / time of day

Data were collected throughout the year and during daylight hours.

Species

Northern gannet (432 birds post-construction), great cormorant (352 birds post-construction), common scoter (341 birds post-construction), common eider (1,034 birds post-construction), black-headed gull (978 birds post-construction), herring gull (1,408 birds post-construction), great black-backed gull (564 birds post-construction), black-legged kittiwake (1,350 birds post-construction), Sandwich tern (2,135 birds post-construction).

Conditions data collected under

Data collected under all conditions in which visibility was at least 1 km.

Location / habitat

A shallow spit, approximately 1 km from shore.

Turbine / array specification

Two turbines spaced 200 m apart with a hub height of 59.4 m above mean sea-level and a rotor diameter of 66 m.

Results

For each species, the change in the proportion of birds flying at altitudes greater than 9.1 m above mean sea-level pre and post-construction are available. For most species, a greater proportion of birds fly above 9.1 m post-construction than pre-construction. The increase in the proportion of gulls flying above 9.1 m varied from 114-238% during the summer and 267-2,900% in the winter. Similarly during the summer, the proportion of gannets flying above 9.1 m increased by 2,800%.

Assessment of methodology

Despite the authors' assurances, it is unlikely that all birds were detected over the full range of the observation area. In particular, birds at lower altitudes may be obscured by waves, or be less visible against the sea surface. As a result, the proportion of birds at lower altitudes may have been under-estimated. In addition, the change in observation platform between pre- and post-construction periods is likely to have afforded an improved view of the observation area. These factors mean that pre- and post-construction comparisons of the estimates of birds at different altitudes may not be reliable. In addition, the presence of the turbines offering a fixed structure with which to assess birds' flight heights against, is likely to have improved the accuracy of estimates of flight heights made post-construction. Finally, by limiting the comparison to birds above 9.1 m, well below the rotor sweep of the turbines, the proportion of birds at risk is likely to be vastly over-estimated.

A4.3 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

Visual observations

Between spring 2007 and December 2009, 405 panorama scans were carried out from a met mast on the edge of the Egmond aan Zee Windfarm. Scans were undertaken once an hour during daylight covering a 360˚ angle around the windfarm with a pair of 10 x 42 binoculars fixed on a tripod. During each observation period, two scans were undertaken, the first to capture birds close to the sea surface and the second to capture birds at greater altitudes. The height of birds was estimated using trigonometry to combine the distance and angle between the bird and observer. Birds could be viewed to a distance of up to 3 km, although imperfect detection is likely to be an issue at these distances. The area covered by each panorama scan is approximately 50% within the windfarm and 50% outside, allowing for simple comparisons to be made of birds inside and outside of the windfarm, although differences were not assessed statistically.

Seasons / time of day

Data were collected during daylight, throughout the year. There was increased effort during the spring and autumn migration periods.

Species

Northern gannet, great cormorant, black-legged kittiwake, black-headed gull, common gull, lesser black-backed gull, herring gull, great black-backed gull, Sandwich tern, small gull spp., large gull spp., gull spp.

Conditions data collected under

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.

Results

Species varied in their vertical responses to wind turbines. Of the 13 species or groups considered, the proportion flying at rotor height was lower inside the windfarm than outside for kittiwake, black-headed gull, northern gannet, great black-backed gull, Sandwich tern and unidentified gull species (no numbers were presented). Large gulls appeared to show little, or no vertical response to the turbines, with roughly the same proportion flying at rotor height inside as outside. In contrast, the proportions of great cormorants, common gulls, little gulls and other small gulls flying at rotor height showed a noticeable increase inside the windfarm.

Assessment of methodology

Data are presented as the proportions of birds at rotor height both within and outside the windfarm. Without any details on the number of birds involved, it is difficult to determine the strength of these data, and the subsequent findings. Of particular concern is the way in which data for unidentified gulls have been presented and the apparent inconsistency in the results for each category which show roughly the same proportion of unidentified large gulls at rotor height inside as outside the windfarm, more small gulls at rotor height inside than outside the windfarm, but unidentified gulls assigned to neither category significantly less likely to be at rotor height within the windfarm. Without more details of the species likely to be covered by each category, and their abundance within the study area, it is difficult to assign levels of confidence to the results presented.

A4.4 Gunfleet Sands I and II

RPS. 2008. Gunfleet Sands Monitoring Report, RPS, London

NIRAS. 2011. Gunfleet Sands 2 Offshore Wind farms. Year 1 Post-construction Ornithological monitoring. NIRAS, Cambridge

GoBe Consultants Ltd. 2012. Gunfleet Sands Offshore Wind farm I & II - Post Construction Year 2 - Marine Licence Environmental Monitoring Report. Prepared for DONG Energy.

Methods

Boat surveys

Pre- and post-construction monitoring data were collected as part of boat surveys following standardised methodologies (Camphuysen et al. 2004). Flying birds were assigned to one of the following flight height bands <5 m, 5- 15 m, 15 -150 m. Pre-construction surveys were carried out between October 2007 and March 2008. Post-construction surveys were carried out between October 2010 and March 2011 and between October 2011 and March 2012. However, differences were not assessed statistically.

Seasons / time of day

Data were collected over winter, during periods of daylight.

Species

Red-throated diver, black-headed gull, common gull, great black-backed gull, gull spp., herring gull, black-legged kittiwake, lesser black-backed gull

Conditions data collected under

No details given.

Location / habitat

Gunfleet Sands I & II offshore windfarms, approximately 7 km from the coast.

Turbine / array specification

Gunfleet Sands I and II contain 48 turbines between them, each with a hub height of 75 m and a rotor diameter of 107 m. The projects cover a total area of 16 km 2.

Results

The proportion of red-throated divers flying at collision risk height declined following the construction of the windfarm, by 39% in winter 2010/11 and by 96% in winter 2011/12. In contrast, the proportion of great black-backed gulls at rotor height showed an increase following construction, by 75% in winter 2010/11 and 53% in winter 2011/12. The proportion of herring gulls at rotor height showed little change between pre-construction years and either post-construction survey. Results for other species were less consistent. For example common gulls showed an increase in the proportion at rotor height in 2010/11 compared to pre-construction data, but a decrease in 2011/12.

Assessment of methodology

Data were collected following a relatively robust methodology and the height bands used were a reasonable match for the dimensions of the rotor swept area of each turbine meaning the proportions of birds at risk height are less likely to be significantly over-estimated. However, the limited duration of pre- and post- construction surveys, reflected in the quantity of data available, means that there may only be limited power to detect significant changes in species flight heights.

A4.5 Nysted/Horns Rev

Blew, J., Hoffman, M., Nehls, G., Hennig, V. 2009. Investigations of the bird collision risk and the responses of harbour porpoises in the offshore windfarms Horns Rev, North Sea, and Nysted, Baltic Sea, in Denmark.

Methods

X-Band Radar

The spring and autumn migration periods were monitored at Horns Rev and Nysted in 2005 and 2006 using x-band radar mounted on vessels anchored in each windfarm. In total, across both windfarms 71.5 days of monitoring were carried out during the spring and 93.5 days during the autumn. Data were captured up to a height of 1,500 m and movements were examined in two height bands <200 m and 200-500 m. All birds tracked for > 100 m and showing a change in movement of >20 m were considered to have changed altitude.

Seasons / time of day

Data were collected throughout spring and autumn in 2005 and 2006.

Species

Having used radar, it was not possible to determine the species captured by the radar.

Conditions data collected under

It was not possible to collect data during periods of strong wind or heavy rain. However, all other conditions were covered.

Location / habitat

Horns Rev 17.9 km from the Danish North Sea Coast.

Nysted 10.8 km from the Danish Baltic Sea Coast.

Turbine / array specification

Horns Rev is an array of 80 turbines covering an area of 21 km 2. Each turbine has a hub height of 70 m and a rotor diameter of 80 m.

Nysted is an array of 72 turbines covering an area of 26 km 2. Each turbine has a hub height of 69 m and a rotor diameter of 82 m.

Results

Across both windfarms, and within the 0-200 m observation band, 4.8% of birds flying towards the windfarm were shown descending by more than 20 m and 13.4% were shown ascending by more than 20 m during the day time. At night time, the values were 2.9% and 13.6% respectively. However, these proportions did not differ significantly from the observations within the 200-500 m band, suggesting that the change in flight heights did not differ from what may be expected to occur by chance and are therefore unlikely to reflect avoidance behaviour.

Assessment of methodology

The rotor-swept area of each turbine covers altitudes from 20-110 m. Consequently, as data were relatively coarse and restricted to all flights within a band of 0-200 m, it may not have been possible to detect responses to turbines. In addition, having used radar, any responses to turbines that had been recorded could not have been identified to species level.

A4.6 Robin Rigg

Natural Power Consultants. 2013. Analysis of Marine Environmental Monitoring Plan Data from the Robin Rigg Offshore Wind farm, Scotland (Operational Year 3). Natural Power, Castle Douglas.

Methods

Boat-based surveys

Pre- and post-construction boat surveys were carried out within the windfarm following standard methodologies (Camphuysen et al. 2004). Birds in flight were assigned to bands of 0-5 m, 6-25 m, 26-34 m, 35-125 m, 126-200 m and >200 m. Surveys were carried out on a bi-monthly basis during pre-construction monitoring (2001-2007), and on a monthly basis during post-construction monitoring (2010-2011). Where sufficient data were available, differences in the proportions of birds flying at rotor height were assessed using a chi-squared test.

Seasons / time of day

Surveys were carried out throughout the year, during daylight.

Species

Common scoter, red-throated diver, diver spp., Manx shearwater, northern gannet, great cormorant, black-legged kittiwake, herring gull, great black-backed gull, gull spp, common guillemot, razorbill, auk spp.

Conditions data collected under

No details given.

Location / habitat

Robin Rigg Offshore Windfarm, 11 km from shore.

Turbine / array specification

Robin Rigg is an array of 60 turbines, each with a hub height of 80 m and a rotor diameter of 88 m. The turbines are spaced at intervals of approximately 500 m.

Results

There were no significant differences in the proportions of birds flying at rotor height during pre- and post-construction surveys for common scoter and red-throated diver. However, the proportion of northern gannet, great cormorant, black-legged kittiwake and large gull species flying at rotor height within the windfarm all increased between pre- and post-construction. However, the low power of the data was noted raising concerns over the validity of the results.

Assessment of methodology

Flight height data were not collected following the standard ESAS methodology and concerns are raised that this is likely to lead to a double counting of individuals, meaning estimates of changes in the proportion of birds at collision risk height may not be reliable.


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