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Waterbirds around
the world
A global overview of the conservation,
management and research of the
world's waterbird flyways
Edited by G.C. Boere, C.A. Galbraith and D.A. Stroud
Assisted by L.K. Bridge, I. Colquhoun, D.A. Scott,
D.B.A. Thompson and L.G. Underhill
EDINBURGH, UK: THE STATIONERY OFFICE
Extract only - complete publication at www.jncc.gov.uk/worldwaterbirds
© Scottish Natural Heritage 2006
First published in 2006 by The Stationery Office Limited
71 Lothian Road, Edinburgh EH3 9AZ, UK.
Applications for reproduction should be made to Scottish Natural Heritage,
Great Glen House, Leachkin Road, Inverness IV3 8NW, UK.
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
ISBN 0 11 497333 4
Recommended citation:
Boere, G.C., Galbraith, C.A. & Stroud, D.A. (eds). 2006.
Waterbirds around the world. The Stationery Office, Edinburgh, UK. 960 pp.
Names used for geographical entities do not imply recognition, by the organisers of the Waterbirds around the world conference or other
supporting organisations or governments, of the political status or boundaries of any particular territory. Names of territories used (and
any alternatives) are included solely to help users of this publication apply information contained within this volume for waterbird
conservation purposes. The views expressed in papers included within this volume do not necessarily represent views of the editors
or the organisations and governments that supported the conference and this publication.
Cover photography:
Whooper Swans Cygnus cygnus arriving at Martin Mere, England. Photo: Paul Marshall.
(www.paulmarshallphotography.com)
Copyright of all photographs used in this publication resides with the named photographers.
Waterbirds around the world
Assessing the degree of habitat loss to marine birds from the
development of offshore wind farms
Anthony D. Fox & Ib Krag Petersen
Department of Wildlife Ecology and Biodiversity, National Environmental Research Institute, Kalø, Grenåvej 14, DK-8410 Rønde,
Denmark. (email: [email protected])
Fox, A.D. & Petersen, I.K. 2006. Assessing the degree of habitat loss to marine birds from the development of offshore wind farms.
Waterbirds around the world. Eds. G.C. Boere, C.A. Galbraith & D.A. Stroud. The Stationery Office, Edinburgh, UK. pp. 801-804.
ABSTRACT
Environmental impact assessment of offshore wind farms
requires an assessment of waterbird habitat loss, both physical
and as a result of behavioural avoidance. This paper briefly
summarizes the aerial survey transect sampling methods and
approach adopted to undertake such assessments at two marine
wind farms constructed in Danish waters in 2003. At present,
bird encounter rates per unit effort on track have been used to
assess the “preferences” of bird species for wind farm and adjacent areas and to make a statistical comparison of abundance and
distribution before and after construction. Preliminary results
from the two case studies are presented. These results suggest
that divers (Gaviidae), grebes (Podicipedidae), gannets
(Sulidae), some seaducks (Anatidae) and auks (Alcidae) avoid
wind farms after the erection of turbines, whilst some species of
gulls (Laridae) and terns (Sternidae) show some preference for
sites in which wind farms have been constructed compared to
the previously undeveloped sites. A description of an improved
application is given. This combines distance sampling and
spatial modelling techniques currently being developed, and will
provide more robust comparisons of waterbird density surfaces
with respect to pre and post-construction development scenarios
to support more effective environmental impact assessment in
marine environments.
turbines because of the confining visual effects, such that even at
avoidance distances less than half the distance between turbines,
net habitat loss equivalent to the size of the wind farm occurs.
Since birds may habituate over time to unfamiliar constructions
in their foraging distribution at sea, there may be a temporal
component to their avoidance responses.
Environmental impact assessment of offshore wind farms
requires a basic evaluation of the significance of such habitat
loss. Indeed, assessment of the consequences at local and population/flyway level may be a foregone requirement, for example,
under environmental criteria placed on construction. Hence, it is
important to quantify habitat loss in a way that accounts for the
spatial and temporal heterogeneity in bird distributions prior to
and after construction. In this short account, we summarize the
approach taken to assess effective habitat loss to foraging waterbirds based on experiences from two wind farms constructed in
Danish inshore waters mainly during 2003. These are situated at
Horns Rev (off the exposed west coast of Jutland in the North
Sea) and Nysted (south of Rødsand in the brackish Baltic). Both
projects have already been widely reported elsewhere (e.g.
Christensen et al. 2004, Kahlert et al. 2004, Petersen et al. 2004),
but are summarized here. We also discuss the current state of
development of the necessary tools required for effective assessment of the degree of habitat loss to foraging birds offshore.
INTRODUCTION
The dramatic development of offshore wind farms in
inshore/nearshore marine waters around Europe in recent years
has focussed attention on the hazards they present to waterbirds
and other migratory birds that encounter these constructions.
Direct impacts, such as result from direct collision, cause
mortality that affect the demography of populations, but local
effects (such as the extra energy costs incurred by avoidance
flights or habitat loss) are more difficult to quantify. Habitat gain
and loss as a result of the construction of wind turbines can be
considered on two spatial and temporal scales. Firstly, long-term
but small-scale change results from the physical loss of feeding
substrate under foundations and anti-scour protection and the
physical gain associated with the creation of these new
substrates. However, since the area of foundations and anti-scour
protection rarely exceeds 2% of the total sea area covered by a
wind farm, this change in food availability is considered trivial
in most instances. Secondly, effective habitat loss may result
from behavioural displacement of foraging birds, the response to
specific stimuli such as rotating turbines and/or the activity of
maintenance vessels in the vicinity. In theory, if birds avoid
coming closer that half the distance between adjacent turbines,
the effective loss of habitat exceeds the entire area of the wind
farm. In practice, birds may avoid going between the rows of
METHODS
The strategic approach adopted in the study of the effects of the
two Danish offshore wind farms has been to use aerial surveys
to describe changes in bird abundance and distribution as a
proxy measure of habitat loss. The problem associated with such
assessments is the very large degree of spatial and temporal
heterogeneity associated with bird distributions in dynamic
media such as inshore marine waters. Benthic feeders (such as
eiders Somateria spp. and scoters Melanitta spp. feeding on
marine bivalve molluscs) may show relatively simple responses
to factors such as water depth and substrate type that determine
the nature and profitability of the benthos they feed upon.
Nevertheless, temporal variation in the abundance of benthic
feeders will be subject to temporal variation in spat settlement
and age class distributions of their prey. Bird species preying on
pelagic fish, such as divers (Gaviidae), grebes (Podicipedidae)
and auks (Alcidae), are even less predictable, dependent upon
temporal and spatial patterns of distribution and abundance of
their highly mobile prey.
To enable a pre and post-construction comparison of the bird
distribution and abundance in such heterogeneous systems, it is
essential to survey and re-survey a sufficiently large geographical area with high temporal frequency. This BACI (before-after
control-impact) type of design should encompass sampling bird
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Waterbirds around the world
Fig. 1. Diagrammatic representation of theoretically constant bird
densities along a transect prior to construction of offshore wind farms
(broken line), compared with post construction (solid line). The features
of interest are the extent of complete habitat loss (solid arrow) and the
extent of reduced densities (broken arrow).
Fig. 2. Diagrammatic representation of theoretical modelled bird densities (with confidence intervals) along a transect sampled prior to
construction of offshore wind farms (pecked line), compared with post
construction (solid line). The features of interest are the extent of
complete habitat loss (solid arrow), the extent of reduced densities
(pecked arrow), and hence the difference in overall densities between the
two samples.
densities within:
• the area physically affected by the construction area;
• an area around this where behavioural avoidance may also
cause an effect (assumed to be a gradient of avoidance with
increasing distance from the turbines); and
• a reference area where bird distributions are likely to be
unaffected by the construction of the wind turbines.
tion area. In doing so, we define the potential impact of loss of
these areas relative to the preference shown by the species for
the entire study area. In a typical analysis, species encounter rate
was calculated for all pre-construction surveys combined, and
compared with the data generated from post-construction
surveys. For these zones, the preference of the most numerously
occurring species is calculated using Jacob’s selectivity index
(Jacobs 1974). Jacob’s selectivity index (D) varies between
-1 (all birds present outside the area of interest) and +1 (all birds
inside the area of interest), and is calculated as:
D = (r - p)/ (r + p - 2rp)
where r = the proportion of birds in the area of interest compared
to the birds in the whole study area, and p = the proportion of the
survey effort in the area of interest compared to the total survey
effort in the whole study area. The difference between the two
proportions is tested as the difference between the observed
number of birds in the area of interest and the number expected
in this area, estimated from the share of the survey effort in relation to survey effort in the total area (one-sample χ2 -test). Tests
are made on the basis of number of observed clusters, rather than
birds, because observations of individual birds fail to meet the
statistical criteria of being independent. However, for some
species a cluster can represent a wide range of number of individual birds, varying from 1 to 26 000 in the case of the Common
Scoter Melanitta nigra, so the use of cluster data may appear
unhelpful.
An alternative approach has been to compare the pre- and
post-construction frequency distribution of birds at increasing
distance intervals out from wind turbines. Using GIS and other
tools to construct species cumulative percentage frequency
distributions of bird numbers in successive 500 m distance intervals away from the wind turbines, it is possible to use non-parametric tests to compare pre- and post-construction distributions
for significant displacement effects.
However, the ultimate aim has been to develop a more
sophisticated suite of analytical tools to permit more robust
comparisons of before/after densities of birds. The use of survey
data collected at different distances from the observer aircraft
provides transect counts of birds assigned to distance categories
out from the transect track-lines. Such a line-transect count
approach allows the use of Distance Sampling techniques
Such sampling needs to be undertaken as frequently as
necessary to characterize changes in temporal abundance
throughout the annual cycle. In two-dimensional space, we may
hypothesize complete bird avoidance within a specific distance
of the turbines (Fig. 1). In this case, the objective is to measure
the area of displaced birds, both in terms of defining the extent
of areas of water without birds and areas of water with reduced
densities relative to the baseline. The ideal objective for any
sampling protocol is therefore to generate bird density surfaces
over large areas of open sea using data:
•
•
•
•
from as large a reference area as possible;
sampled as simultaneously as possible;
gathered with the greatest level of spatial precision
possible;and
using observation platforms that cause least disruption to the
patterns of abundance and distribution of undisturbed birds.
For this reason, the Danish studies have adopted aerial
survey using high-winged twin-engined aircraft to cover large
areas of open marine waters as rapidly as possible using internationally agreed standardized data collection protocols (described
in Camphuysen et al. 2004).
Initially, a very simple analytical approach has been adopted
to analyse these transect count data, based on encounter rates of
birds or bird clusters observed on transects per unit effort. This
approach determines the relative number of birds of different
species that would be susceptible to potential disturbance effects
from the wind turbines based on encounter rate corrected for
observation effort. The method assesses the relative importance
of the wind farm area and the adjacent waters, generally a zone
within 2 and 4 km of the outermost turbines of a wind farm
(see methods in Petersen et al. 2004). The method describes the
“preference” of bird species for the wind farm area and adjacent
zones of differing extent immediately adjacent to the construc-
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Waterbirds around the world
backed Gulls L. marinus, Little Gulls L. minutus and
Arctic/Common Terns Sterna paradisea/S. hirundo showed a
shift from avoidance before construction to a preference for the
wind farm area after construction (Petersen et al. 2004).
At Nysted, Long-tailed Ducks Clangula hyemalis and
Common Eiders Somateria mollissima showed a reduced preference for the wind farm area (and zones within 2 and 4 km of it)
after the erection of the wind turbines. Herring Gulls showed a
slight increase in preference for the wind farm area and the
zones around it after construction (Kahlert et al. 2004).
(Buckland et al. 2001) to generate bird densities, by modelling
detectability functions to correct bird density estimates for the
decline in detectability probability with increasing distance from
the observer. The use of such techniques also enables the incorporation of factors and covariates (such as individual observer
functions, differences in sea state and light conditions, etc.) into
modelled densities of birds encountered. The ultimate objective
for this project has been to develop spatial modelling techniques
that use line-transect counts as samples and generalized additive
models to construct bird density surfaces as a function of
spatially explicit covariates (e.g. Hedley et al. 1999, Hedley &
Buckland 2004, Clarke et al. 2004). This method offers an
approach to the theoretical objectives established in Fig. 1 by
constructing a modelled bird density surface with confidence
intervals over extended areas of sea generated from aerial linetransect census data (see Fig. 2). For benthic feeding birds, the
covariates used in the predictive-modelling exercise could
include environmental factors such as water depth which determine profitability of shallow inshore waters (e.g. Common
Scoters forage more in shallow water depths than would be
expected by chance; see Fig. 17 in Petersen et al. 2004). In the
fullness of time, other environmental covariates, such as bottom
substrate type and bottom aspect can be incorporated to improve
the effectiveness of such model estimates. For seabirds
dependent on a more dynamic food base, such as pelagic fish,
the challenges to generating density surfaces are considerably
greater. However, incorporation of macro-environmental parameters, such as current, salinity and water temperature profiles
(which are now routinely modelled throughout the water column
around many European coasts) which correlate with prey abundance, offers some opportunities to generate bird density
surfaces for these organisms as well.
At present, software to generate such modelled density
surfaces is still being developed in collaboration with the Centre
for Research into Ecological and Environmental Modelling at
the University of St Andrews in Scotland, for implementation in
the near future.
DISCUSSION
The bird studies being carried out at Nysted and Horns Rev during
the period 1999-2006 were initiated under the terms and conditions placed upon the granting of permission to construct wind
farms at the two sites by the Danish authorities. These studies
have been carried out before, during and after construction of both
wind farms. The installation of wind turbines was finished in
autumn 2002 (Horns Rev) and summer 2003 (Nysted). However,
the construction phase was too short to offer any opportunity to
assess the effects of the physical construction of turbines on bird
distribution. Construction activities coincided with periods of the
year when fewest feeding birds were in the vicinity (by prior
design), with the result that no assessment could be made of the
disturbance effects of building work during that phase.
Furthermore, the data reported here (for the period up to 2004)
represent material gathered from one year or less into the initial
operational phase of the wind farms. For this reason, it is not
possible to quantify natural variation between years, seasons,
species and sites and the possible habituation effects during the
operational phase. Therefore, it must be emphasized that these
results are to be considered as preliminary, and must await further
compilation of data before firm conclusions can be drawn with
respect to the impact on birds. The final environmental impact
assessment for the two wind farms will be undertaken upon termination of the environmental monitoring programmes in 2006.
There remains considerable scope to improve on these
methods and to test many of the assumptions associated with their
use. In particular, distance sampling necessitates that all objects
on the track-line are observed from the count platform, an
assumption that has considerable bearing on the ability to
generate unbiased density estimates. Studies to assess whether
this assumption is met, using double-platform repeat counting,
have been attempted, including the use of two aircraft and vertical
photographic techniques to capture scenes of the distribution of
birds on the sea surface to which count observers were exposed in
the following aircraft. Such techniques proved so effective, and
the imagery quality sufficient to enable automated computer identification and counting of bird “objects” on the photographs, that
alternative methods of counting birds at sea have presented themselves. The use of geo-rectified vertical photography of large
areas of sea surface, and subsequent computer based pattern
recognition software to identify, position with great spatial accuracy and ultimately count birds on that surface, frees the need for
distance sampling to generate bird densities, and offers some very
exciting prospects for future developments in this field.
RESULTS
Results from tests based on the numbers of bird clusters encountered have been used to compare pre-construction and postconstruction distributions to look for changes in preference for
the wind-farm area and surroundings between the two “treatments”. Use of the Jacobs selectivity index has suggested
changes in distribution of different species, both in terms of
avoidance of, and attraction to, the structures, as outlined below
(see also Christensen et al. 2004 and Petersen et al. 2004).
At both sites, analysis of the preference indices calculated
for different species prior to construction confirmed that the
majority of waterbirds avoided the wind farm area at both sites.
Bird densities were generally low before any construction activities on the site, making comparisons after construction difficult,
especially since at present there is only a single post-construction year available for comparisons.
At Horns Rev, divers, Northern Gannets Sula bassana,
Common Scoters and Guillemots/Razorbills Uria aalge/Alca
torda showed an increased avoidance of the wind farm area (and
zones within 2 and 4 km of it) after the erection of the wind
turbines. In contrast, Herring Gulls Larus argentatus showed a
decreased avoidance of the wind farm area, while Great Black-
ACKNOWLEDGEMENTS
We gratefully acknowledge the help and support of our NERI
colleagues, especially the aerial survey observers, Ib Clausager,
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Clarke, E.D., Spear, L.B., McCracken, M.L., Marques,
F.F.C., Borchers, D.L., Buckland, S.T. & Ainley, D.G.
2004. Validating the use of generalized additive models
and at-sea surveys to estimate size and temporal trends
of seabird populations. Journal of Applied Ecology 40:
278-292.
Hedley, S.L. & Buckland, S.T. 2004. Spatial models for line
transect sampling. Journal of Agricultural, Biological
and Environmental Statistics 9: 181-199.
Hedley, S.L., Buckland, S.T. & Borchers, D.L. 1999. Spatial
modelling from line transect data. Journal of Cetacean
Research and Management 1: 255-264.
Jacobs, J. 1974. Quantitative measurements of food selection.
Oecologia 14: 413-417.
Kahlert, J., Petersen, I.K., Fox, A.D., Desholm, M. &
Clausager, I. 2004. Investigations of birds during
construction and operation of Nysted offshore wind farm
at Rødsand - Annual status report 2003. Report request.
Commissioned by Energi E2 A/S. National
Environmental Research Institute. Available at:
http://uk.nystedhavmoellepark.dk/upload/pdf/Birds2003
.pdf.
Petersen, I.K., Clausager, I. & Christensen, T.K. 2004. Bird
numbers and distribution in the Horns Rev offshore wind
farm area. Annual status report 2003. Report commissioned by Elsam Engineering A/S. National
Environmental Research Institute. Available at:
http://www.hornsrev.dk/Miljoeforhold/miljoerapporter/Bird_numbers_2003%20status_report.pdf.
Johnny Kahlert, Thomas Kjær and Mark Desholm. Our thanks
also to David Borchers, Sharon Hedley and colleagues at
St Andrews University for support with developing analytical
techniques and to E2, Elsam and their staff for funding and
support for the two Danish case studies reported here.
REFERENCES
Buckland, S.T., Anderson, D.R., Burnham, K.P., Laake, J.L.,
Borchers, D.L. & Thomas, L. 2001. Introduction to
Distance Sampling - Estimating Abundance of
Biological Populations. University Press, Oxford.
Camphuysen, C.J., Fox, A.D., Leopold, M.F. & Petersen, I.K.
2004. Towards standardised seabirds at sea census techniques in connection with environmental impact assessments for offshore wind farms in the U.K. A comparison
of ship and aerial sampling methods for marine birds, and
their applicability to offshore wind farm assessments.
Report to Collaborative Offshore Wind Research into the
Environment (COWRIE), Crown Estate Commissioners,
London. Available at: http://www.thecrownestate.co.uk/
1352_bird_survey_phase1_final_04_05_06.pdf.
Christensen, T.K., Hounisen, J.P., Clausager, I. & Petersen,
I.K. 2004. Visual and radar observations of birds in relation to collision risk at the Horns Rev offshore wind farm.
Annual status report 2003. Report request.
Commissioned by Elsam Engineering A/S. National
Environmental Research Institute. Available at:
http://www.hornsrev.dk/Miljoeforhold/miljoerapporter/
Visual_radar_observations_2003_status_report.pdf.
The Nysted Offshore Wind Farm in the Danish part of the Baltic Sea consists of 72 turbines situated c. 11.5 km south of the island of Lolland and
covering an area of 24 km2. Water depth in the area is 6 - 9.5 m. The windfarm has a total power capacity of 165.6 MW, and is the world's largest
offshore wind farm. (Photo provided by Energy E2). Photo: Ib Krag Petersen.
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