Towards standardised seabirds at sea census techniques in connection with environmental impact assessments for offshore wind farms in the U.K.

Abstract

· The coastal and offshore waters of the UK are of global importance for several species of seabirds. The United Nations Law of the Seas and the establishment of Exclusive Economic Zones gives coastal states extensive rights but also obligations over marine areas, including the assessment of potential effects of activities on the marine environment. The Crown Estate, as landowner of the seabed out to the 12 nautical mile territorial limit plays an important role in the development of the offshore wind industry by leasing areas of seabed for the placing of turbines. The planned erection of large numbers of offshore wind turbines has underlined our lack of knowledge relating to the distribution, abundance and habitat requirements (foraging ecology) of marine birds.
· As part of the Environmental Impact Assessments for offshore wind farms, the need for detailed knowledge on spatial and temporal patterns in seabird distribution has been identified. Dedicated censuses to sample the numbers and distribution of seabirds are a basic requirement for developers, to describe bird densities within, and in the immediate vicinity of, the construction area. Studies performed need to be related to some greater area studies, in order to assess the relative and the actual importance of the construction area for the species involved.
· This document evaluates existing census techniques and determine the best currently available methods for defining bird distribution and abundance at sea. The underlying question is twofold: (1) what are the research objectives and what data are required for EIAs for offshore wind farms, and (2) how good are existing census techniques at fulfilling the objectives?
· In order to assess the potential impact of the construction of an offshore wind farm and to understand how such a construction is likely to affect the birds associated with a site, dedicated research is required. The coupling of bird census data with geographical, hydrographical, and biological measurements is essential to begin to understand how an offshore construction such as a wind farm is likely to affect an area and how the seabirds associated with a site are most likely to respond. Natural variability issues are addressed and existing census techniques have been evaluated for their potential to provide data that can be used to describe habitat characteristics and area usage by seabirds.
· The two observation tools discussed in this study, aerial and ship-based surveys, potentially provide similar data for as far as basic seabird counts are concerned (accurate numbers, accurate maps). Census techniques are similar (distance techniques using parallel bands of known width), but the level of detail for individual species is considerably less during aerial surveys. Aerial surveys are quick, so enabling coverage of larger areas per unit time, and relatively cheap, whereas ship-surveys are more time-consuming.
· Data obtained during aerial surveys may be combined with environmental parameters in a correlative approach, whereas the advantage of a ship is that such parameters can often be collected simultaneously. The slower approach with vessels allows detailed observations on seabird behaviour (habitat utilisation, feeding conditions) and diurnal/tidal fluctuations in seabird abundance and distribution.
· The acquisition of information about migration routes, direction or height of flight, detailed spatial and temporal distribution require intensive radar and direct observation in the vicinity of a proposed wind farm development to determine bird use of the area and to predict collision impact probabilities under a range of differing temporal (day/night) and weather conditions. Similarly, assessment of actual collision risk and collisions after construction necessitates static measuring devices (such as infra-red movement triggered video surveillance and vibration detection equipment currently under development). However, these tools are not addressed further in this report.

http://www.offshorewindfarms.co.uk/Downloads/1352_bird_survey_phase1_final_04_05_06.pdf

Full text

COWRIE – BAM- 02-2002
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
Kees (C.J.) Camphuysen
1
, Tony (A.D.) Fox
2
, Mardik (M.F.) Leopold
3
& Ib Krag Petersen
1
Koninklijk Nederlands Instituut Voor Onderzoek Der Zee (Royal NIOZ), The Netherlands
2
National Environmental Research Institute, Denmark
3
Alterra, The Netherlands
Final version: April 2004
This report was commissioned by COWRIE
Koninklijk Nederlands Instituut voor Onderzoek der Zee
Royal Netherlands Institute for Sea Research
PO Box 59
1790 AB Den Burg
Landsdiep 4
1797 SZ t’Horntje
Texel

1

2
Contents
Executive summary 4
Recommended methodology for ship-based surveys 4
Recommended methodology for aerial surveys 5
Introduction 6
Aim of the project 8
Existing approaches 9
Objectives and methods of early offshore observations 9
Recent work (1) Ship-based surveys 9
Recent work (2) Aerial surveys 9
COWRIE research objectives 11
Patterns in seabird distribution and abundance 11
Evaluation of disturbance and habitat loss 12
Migratory pathways 12
Evaluation of collision risks 12
Natural variability 13
Scale and variability 13
Migratory pathways (routes, direction of flight, seasonal patterns) 13
Weather effects 13
Diurnal patterns and tidal influences 13
Foraging areas 14
Factors explaining seabird distribution and abundance 14
Survey techniques 15
Line transect technique using parallel strips (ship and aerial surveys) 15
Line-transect technique using individual distances to the track line for marine mammals 15
Point transect techniques 16
Seaduck and diver surveys from ships: modifications of ESAS protocol 17
Geographical accuracy 17
Ship-based surveys 18
Strip- and line-transect techniques for seabirds 18
Behaviour of birds 19
Flying height of birds 19
Training of observers, observer quality 19
Avoiding attraction 19
Additional data 20
Recommended methodology, ship-type, and observers 20
Conclusions 20
Aerial surveys 22
Transect bands 22
Choice of airframe 22
Survey flight speed and altitude 24
Data collection and observer training 24
Spatial precision and recording protocols 24
Data format 25
Species 25
Constraints on counting methods 25
Current methods of data presentation and analysis 26
Potential future developments 26
Recommended methodology, airframe characteristics, and observers 26

3
Conclusions 27
Transect sampling design 29
Systematically arranged parallel transect lines 29
Grid orientation 29
Transect intervals 29
Diurnal variation 29
Seabird behaviour 30
Conclusions 31
Acknowledgements 32
References 33
Annex 1: Recording seabird behaviour (applicable for ship-based surveys only) 36

4
Executive summary
• The coastal and offshore waters of the UK are of global importance for several species of seabirds. The
United Nations Law of the Seas and the establishment of Exclusive Economic Zones gives coastal states
extensive rights but also obligations over marine areas, including the assessment of potential effects of
activities on the marine environment. The Crown Estate, as landowner of the seabed out to the 12 nautical
mile territorial limit plays an important role in the development of the offshore wind industry by leasing
areas of seabed for the placing of turbines. The planned erection of large numbers of offshore wind
turbines has underlined our lack of knowledge relating to the distribution, abundance and habitat
requirements (foraging ecology) of marine birds.
• As part of the Environmental Impact Assessments for offshore wind farms, the need for detailed knowledge
on spatial and temporal patterns in seabird distribution has been identified. Dedicated censuses to sample
the numbers and distribution of seabirds are a basic requirement for developers, to describe bird densities
within, and in the immediate vicinity of, the construction area. Studies performed need to be related to
some greater area studies, in order to assess the relative and the actual importance of the construction
area for the species involved.
• This document evaluates existing census techniques and determine the best currently available methods
for defining bird distribution and abundance at sea. The underlying question is twofold: (1) what are the
research objectives and what data are required for EIAs for offshore wind farms, and (2) how good are
existing census techniques at fulfilling the objectives?
• In order to assess the potential impact of the construction of an offshore wind farm and to understand how
such a construction is likely to affect the birds associated with a site, dedicated research is required. The
coupling of bird census data with geographical, hydrographical, and biological measurements is essential
to begin to understand how an offshore construction such as a wind farm is likely to affect an area and how
the seabirds associated with a site are most likely to respond. Natural variability issues are addressed and
existing census techniques have been evaluated for their potential to provide data that can be used to
describe habitat characteristics and area usage by seabirds.
• The two observation tools discussed in this study, aerial and ship-based surveys, potentially provide similar
data for as far as basic seabird counts are concerned (accurate numbers, accurate maps). Census
techniques are similar (distance techniques using parallel bands of known width), but the level of detail for
individual species is considerably less during aerial surveys. Aerial surveys are quick, so enabling
coverage of larger areas per unit time, and relatively cheap, whereas ship-surveys are more time-
consuming.
• Data obtained during aerial surveys may be combined with environmental parameters in a correlative
approach, whereas the advantage of a ship is that such parameters can often be collected simultaneously.
The slower approach with vessels allows detailed observations on seabird behaviour (habitat utilisation,
feeding conditions) and diurnal/tidal fluctuations in seabird abundance and distribution.
• The acquisition of information about migration routes, direction or height of flight, detailed spatial and
temporal distribution require intensive radar and direct observation in the vicinity of a proposed wind farm
development to determine bird use of the area and to predict collision impact probabilities under a range of
differing temporal (day/night) and weather conditions. Similarly, assessment of actual collision risk and
collisions after construction necessitates static measuring devices (such as infra-red movement triggered
video surveillance and vibration detection equipment currently under development). However, these tools
are not addressed further in this report.
Recommended methodology for ship-based surveys
Recommended census techniques for ship-based seabird surveys, as part of an EIA, are line-transects with sub-
bands and with snap-shots for flying birds, and incorporating the full behaviour module recording detailed
information on species, sex and age where feasible, foraging behaviour, flying height. Whenever possible,
hydrographical data, such as sea surface temperature, salinity, water depth should be continuously and
synoptically monitored. For a minimum set-up, the following techniques and qualifications are recommended.
Line-transect methodology is recommended with a strip width of 300m maximum.
Subdivision of survey bands to allow corrections for missed individuals at greater distances away from the
observation platform (recommended subdivision for swimming birds: A= 0-50m, B= 50-100m, C=100-
200m, D= 200-300m, E= 300+m or outside transect; all distances perpendicular to the ship).
No observations in sea state 5 or more to be used in data analysis for seabirds, data not usable for marine
mammals above sea state 3.
Survey time intervals are recommended to be 1 or 5 min intervals (range 1-10m, longer time intervals are
acceptable when less resolution of data is required; short intervals are preferred in small study areas), with
mid-positions (Latitude, Longitude) to be recorded or calculated for each interval.

5
Preferred ship's speed should be 10 knots (range 5-15 knots).
Preferred ship type is a motor vessel with forward viewing height possibilities at 10m above sea level
(range 5-25m), not being a commercial or frequently active fishing vessel.
Preferred ship-size: stable platform, at least 20m total length, max. 100m total length
Bird detection by naked eye as a default, except in areas with wintering divers Gaviidae. Scanning ahead
with binoculars is necessary, for example to detect flushed divers.
Two competent observers are required per observation platform equipped with range-finders (Heinemann
1981), GPS and data sheets; no immediate computerising of data during surveys to maximise attention on
the actual detection, identification and recording.
Observers should have adequate identification skills (i.e. all relevant scarce and common marine species
well known, some knowledge of rarities, full understanding of plumages and moults).
Observers must be trained by experienced offshore ornithologists under contrasting situations and in
different seasons.
A high resolution grid should be deployed, covering an area at least 6x the size of the proposed wind farm
area, including at least 1-2 similar sized reference areas (same geographical, oceanographical
characteristics), and preferably including nearby coastal waters (for nearshore wind farms only).
Survey grid lines are recommended to be at least 0.5nm apart, maximum 2nm apart, and the grid should be
surveyed such that time of day is equally distributed over the entire area (changing start and end time over
the area to fully comprehend effects of diurnal rhythms in the area)
The cost-effectiveness of the ship-based surveys are greatly enhanced if the vessel can be equipped with
an Aquaflow (logging surface water characteristics including temperature, fluorescence (chlorophyll), and
salinity logging hydrographical information simultaneously).
The cost-effectiveness of the ship-based bird surveys can be greatly enhanced if combined with other
surveys, such as those of marine mammals, for which a specialist observer and different methods will be
required.
The cost-effectiveness can be further enhanced by counting birds on both sides of the ship, i.e. cover two
strips, for which additional observers will be required.
Recommended methodology for aerial surveys
For a minimum set-up, the following techniques and qualifications are recommended.
 Twin-engine aircraft (for safety and endurance)
 High-wing aircraft with excellent all round visibility for observers (e.g. twin-engine Partenavia P-68
Observer)
 Line-transect methodology is recommended with sub-bands.
 Transects should be a minimum of 2 km apart to avoid double-counting whilst allowing the densest
coverage feasible
 Flight speed preferably 185 km h
-1
at 80 m altitude
 Subdivision of survey bands to allow calculations of detection probabilities (recommended are 44-163m,
164-432m, 433-1000m, with a declination in degrees from the horizon being 60-25°, 25-10°, and 10-4°
respectively for the Partenavia P-68 at 80m)
 Use of an inclinometer to measure declination from the horizon
 Two trained observers, one covering each side of the aircraft, with all observations recorded continuously
on dictaphone
 GPS positions are recorded at least every 5 seconds (computer logs flight track)
 The time of each bird sighting should be recorded, ideally to the nearest second, but within 10 seconds
accuracy, using a watch attached to the window of the plane.
 No observations in sea states above 3 (small waves with few whitecaps)
 All waterbirds should be recorded to the best level of identification (species or group)
 Sampling units are single birds or groups of birds within the three transect bands

6
Introduction
Major development of offshore wind power in the UK is expected in order to meet the UK Government's
commitment to renewable energy targets (http://www.thecrownestate.co.uk/). The Crown Estate, as landowner of
the seabed out to the 12 nautical mile territorial limit plays an important role in the development of the offshore wind
industry by leasing areas of seabed for the placing of turbines. The Crown Estate established a Trust Fund
administered by a Steering Group drawn from the offshore wind industry, government and conservation
organisations. The Steering Group, named COWRIE (Collaborative Offshore Wind Research into the Environment)
has identified and prioritised environmental studies that will be commissioned to inform the offshore wind farm
industry as a whole.
The requirement of many marine birds for shallow, productive, nearshore waters combined with the limited extent
of this resource in the UK and with the preference of wind farm developers to site turbines in shallow waters has
resulted in concerns of potential negative effects on seabirds. For these top-predators in the marine environment,
the establishment of an offshore construction such as a wind farm could potentially have a number of negative as
well as positive effects. Habitat loss, more specifically the loss of foraging areas, restrictions of commercial
fisheries (and the associated reductions in discards and offal provided as artificial sources of food), and the risk of
collisions and death are obvious negative side-effects. For migratory seabirds and coastal nesting birds with
frequent foraging trips from land to offshore feeding sites, the barrier effects of offshore wind turbines in localised
areas cannot yet be discounted and must be considered. Positive effects of the construction of turbines may be
that offshore constructions could provide roosting platforms or locally enhance foraging conditions to such an
extent that some species or populations might profit from them.
COWRIE (COWRIE Steering Group, 22nd August 2002) recognised that the coastal and offshore waters of the UK
are of global importance for several species of resident and migratory marine birds. Many marine bird species
utilise shallow productive waters at different stages of their annual cycle, yet the general understanding of the
marine environment remains poor compared to that of terrestrial and freshwater systems. The planned erection of
large numbers of offshore wind turbines throughout European coasts from Estonia to Spain has underlined our lack
of knowledge relating to the distribution, abundance and habitat requirements (foraging ecology) of marine birds.
The United Nations Law of the Seas and the establishment of Exclusive Economic Zones gives coastal states
extensive rights but also obligations over marine areas, including the assessment of potential effects of activities on
the marine environment under Article 206. Increasingly, domestic and international legislation requires
Environmental Impact Assessment (EIA) of development projects in offshore waters (e.g. the EIA and Strategic
Environmental Assessment (SEA) Directives of the European Union). Many states are already bound by
international agreements and legislation (such as the Ramsar Convention and European Union Birds Directive) to
maintain migratory bird populations throughout the annual cycle, including the provision of reserves and the
general protection of habitat.
Proper EIAs should investigate all potential effects of the establishment and development of wind farms on marine
wildlife, but that is beyond the scope of this document. As part of the EIAs for offshore wind farms, the need for
detailed knowledge on spatial and temporal patterns in seabird distribution has been identified. Fundamental to this
process, is the simple definition of the distribution and abundance of marine birds in time and space. As a
minimum, there is a requirement upon states to define the most important bird areas (potentially for site safeguard)
but ultimately the process should aim to describe the overall distribution and abundance of particular populations
throughout their annual cycle. The process is severely hampered by natural variability and by the long-distance
migratory nature of many marine species, which often use very distant areas for breeding, moulting, staging and
wintering, such that there is great seasonal variation in their distribution and abundance. Factors affecting prey
availability, including access to food supplies, also vary in time and space, and the general abundance of a species
varies as a result of differential patterns of survival and reproductive output, imposing further variation on patterns
of distribution and abundance.
The need for the establishment of common standards in survey of offshore marine birds has been drawn into sharp
focus by the current proposals to construct large wind farms in marine waters around the coasts of Europe. Many of
the proposed wind farms are extensive in area and most planned developments involve the construction of turbines
500-800 m apart, in wind farms covering several square kilometres, so the spatial scale of these developments
necessitates mapping bird densities at high spatial resolution (of a few hundred metres) over extensive areas (tens
of square kilometres). At the local level, dedicated censuses to sample the numbers and distribution of seabirds are
a basic requirement upon developers, to describe bird densities within, and in the immediate vicinity of, the
construction area. In order to assess the potential impact of the construction of, for instance, an offshore wind farm
and to understand how such a construction is likely to affect the birds associated with a site, dedicated research is
required. Any studies performed need to be related to some greater area studies, in order to assess the relative
and the actual importance of the construction area for the species involved. The cumulative description of bird
densities over time and space enables some assessment of the relative importance of the impact area relative to

7
other areas used by the same species. The routine coupling of bird census data with geographical (e.g. depth,
substrate, distance to land), hydrographical (water masses), and biological measurements (e.g. benthic
communities, fish abundance) will further enhance the understanding of the actual habitat characteristics of a given
area and their influence on the distribution of marine birds. Such data is essential to begin to understand how an
offshore construction such as a wind farm is likely to affect the birds associated with a site.
Given the recent round of proposals for offshore wind farm developments in shallow inshore areas and the
expected future developments in this area, it is essential to obtain some consensus on common standards and
best practice in survey techniques used to describe the distribution and abundance of marine birds in key areas.
For this reason, COWRIE has issued an invitation to tender for a project comparing ship and aerial sampling
methods for marine birds and their applicability to offshore wind farm assessments. Despite reasonably complete
data on broad distribution patterns of seabirds around the UK, lack of detailed understanding about local
distribution, at the scale of wind farm sites, temporal variability of numbers and the underlying determinants of their
timing of occurrence was identified. This document evaluates existing census techniques and determines the best
currently available methods for defining bird distribution and abundance at sea. The underlying question is twofold:
(1) what are the research objectives and what data are required for EIAs for offshore wind farms, and (2) how good
are existing census techniques at fulfilling the objectives?
Arctic Tern with sandeel returning to colony, Farne Islands, summer 2003 (CJ Camphuysen)

8
Aim of the project
The overall aim of the project is to produce a standardised guidance document/manual for bird counts in relatively
small areas of sea, using either ships or aircraft as observation platforms (but not necessarily always both), for all
involved in the offshore wind energy industry. The protocol will offer guidance to optimise accuracy and minimise
bias when estimating bird numbers, while taking into account spatial and temporal variability, underlying
determinant factors and the specific needs of an individual project. Existing methodologies for sampling seabirds at
sea have therefore been reviewed and compared; keeping in mind the need to provide information on the scale
associated with offshore wind farms.
The outcome of this exercise, a set of guidelines, details the strengths and weaknesses of a range of recorded
parameters within each method, the circumstances under which different approaches would be recommended, and
recommends standard sampling procedures for both. This standardised protocol for conducting seabird surveys at
sea in connection with any offshore wind farm development around the UK, using agreed common standards and
optimal methodologies, will improve the comparability of data from different future studies. Consultation on the
proposed methodology has been via written comments, based on a draft text posted at the COWRIE web site, and
discussions at an international workshop in Aberdeen, Scotland, November 2003. This final document is the result
of these consultations. The agreed protocol for assessing (changes in) seabird numbers in wind farm EIAs for the
UK are guidelines for any organisation within the UK examining the problem at any site within the domain of the
Crown Estate (shallow coastal seas) in the foreseeable future.
At the international workshop in Aberdeen, it was noted that a standardised protocol will never be able to meet the
most detailed of specific requirements at certain sites. The protocol proposed here ensures adequate data
sampling in marine (coastal) areas, using either aircraft or ship. Specific problems, such as highly localised flyways
of foraging birds, complex shorelines, the location of migration routes, poor weather conditions, may not be
addressed using this same protocol or may require specific adjustments. Since it will be hard to foresee all the
peculiarities and research objectives for wind farms in UK coastal waters, the establishment of a board of experts is
suggested. This board should be consulted where the protocol proposed here is insufficient, or when an adjusted
research protocol has to be critically evaluated.
Seabirds at sea can be counted from either platform following appropriate observation protocols, and accurate
density estimates can be obtained from the air as well as at sea level. Important differences occur, however, and
these differences are most important when choosing to use either an aircraft or a boat. Ship-based surveys, for
example, provide a higher level of accuracy in species identification and assessments of age and behaviour of
seabirds at sea, important in studies where the distribution of seabirds in areas needs background information to
explain and measure natural variability in the system. Aircraft can work areas that are completely or virtually
inaccessible to ships of recommended size and may be more effective in counting certain species groups that are
easily disturbed by traffic such as seaduck and divers.
The choice between either craft, apart from the issue of availability, has to be made with specific research
objectives in mind. Since either method has both advantages and disadvantages, the strong points and
weaknesses of ships and aircraft are highlighted in the present document, and linked to specific research
objectives, so that any wind farm developer could make a choice based on local circumstances and particular
requirements. There is not just one 'best' research tool to be recommended for all places and circumstances. The
pros and cons of either method have been listed with annotations.

9
Existing approaches
Objectives and methods of early offshore observations
Early researchers have used several methods for counting birds at sea (Powers 1982), but very few managed to
collect and analyse their data in a systematic manner and tried to describe different areas on the basis of bird data.
The sinking of the oil tanker Torrey Canyon at Land's End in 1967 and the associated mass mortality of (oiled)
seabirds gave a clear sign, however, that our knowledge of the offshore distribution of seabirds was still very
incomplete. When gas- and oil exploration activities in the North Sea developed rapidly in the 1970s, the need for
adequate data became even more urgent. When asked for specific advice with respect to the densities of
(vulnerable) seabirds in different areas of the North Sea, there was little more than maps of breeding colonies and
the expectation that seabird numbers were probably relatively high in the waters around them. The Canadian
Wildlife Service had developed and deployed a useful method to study seabirds at sea in Canada and to analyse
the results with the use of a computer (Brown et al. 1975). This method, the strip-transect technique, formed the
basis of work conducted by JNCC’s Seabirds At Sea Team formed in the late 1970s. The strip-transect method
was thought to be the most useful at the time, cost-effective and repeatable (Tasker et al. 1984). The first results of
this work were published in the early and mid-1980s (Blake et al. 1984; Tasker et al. 1987). The strip-transect
method, with a snapshot for flying birds (explained later in this document), was adopted by most workers around
the North Sea as an easy and repeatable standard method in an attempt to be able to join forces while mapping
large areas of the North Sea. It should be highlighted that the method was refined soon after the publication by
Tasker et al. (1984), using parallel narrow strips within the band transect to allow for corrections for birds missed at
greater distances from the observation platform (Komdeur et al. 1992). With this modification, the line-transect
technology became adopted (see below). The establishment of a joint database (the European Seabirds at Sea
database, ESAS) was a further important step to collect, store and utilise a large amount of comparable data in a
single format.
Recent work (1) Ship-based surveys
The ESAS strip-transect method (Tasker et al. 1984), slightly revised to a line-transect technique, is still the
backbone of modern ship-based surveys of seabirds at sea in NW European waters (Camphuysen & Leopold
1994; Durinck et al. 1994; Stone et al. 1995; Skov et al. 1995; Bloor et al. 1996; Offringa et al. 1996; Pollock et al.
1997; 2000; Maes et al. 2000; Taylor & Reid 2001; Mitschke et al. 2001; Seys 2001; Skov et al. 2002). Results
have been analysed to answer the more specific questions about the vulnerability of different sea areas for oil
pollution, and vulnerability indices were used to transform plain densities at the species level into densities/levels of
vulnerability (Tasker et al. 1990; Carter et al. 1993; Webb et al. 1995; Williams et al. 1995; Begg et al. 1997; Maes
et al. 2000). Since the late 1970s, joint knowledge of offshore seabird distribution has increased substantially, as a
result of several large programmes of seabirds at sea studies (NCC, later Joint Nature Conservation Committee
(JNCC), culminating in the establishment of the database. The standardisation of methodology at a very early
stage, followed by the adoption of such methods by a large, international group of researchers and organisations
(ESAS), were the backbone of a success-story that has resulted in a number of atlases summarising seabird
distribution patterns in most of North West Europe and in the Baltic. Waterfowl counts in coastal wetlands have
been conducted at least since the 1960s in many European countries, and offshore sites have increasingly been
incorporated in the research set-up of these surveys (Rüger et al. 1986; Laursen 1989; Rose & Scott 1994; Delany
et al. 1999).
More recently, ESAS has focussed more on the marine ecological background to the distribution of
seabirds at sea (e.g. Harrison et al. 1994, Garthe 1997; Camphuysen & Webb 1999). Studies wished to address
other aspects of the marine life of seabirds at sea by using ESAS data and shortcomings in the material led to
further refinements, again while keeping the underlying framework intact (e.g. Camphuysen & Webb 1999;
Camphuysen & Garthe 2001). The ESAS coding structure is now such that each of the outlying methods can be
identified, so that although there is one joint database format, different methods can be entered and selected for
subsequent analysis.
Recent work (2) Aerial surveys
Although aerial survey techniques have been used in European offshore waters for many years, their use has been
relatively limited, possibly because of the high financial costs involved. Their development was accelerated in the
1960s, especially in Denmark, following the pioneering work of Joensen (1968, 1973, 1974). The technique at that
time was highly limited by the ability of pilots and observers to navigate with any accuracy out of range of
navigation beacons or sight of the coast. The surveys at that time were carried out at a variety of altitudes between
50 and 300 metres, according to weather conditions, habitat and species. The routes and extent of coverage
undertaken varied between years, but essentially the technique aimed to record and describe all aggregations of
seabirds encountered along the areas covered by the aerial survey aircraft (Joensen 1974). The objective at that
time was to map the larger concentrations and assess the overall numbers and distributions of birds at the national
level, rather than provide a statistical basis for comparisons in time and space. Joensen (1974) was well aware of
the difficulties involved with sampling bird distributions based on this type of aerial survey, but these assessments

10
were the first ever attempts to determine the numbers of birds using the offshore waters around Denmark and were
a remarkable contribution at the time.
In Britain, aerial surveys have been conducted side by side with ship-based surveys, for example to cover
coastal areas that are difficult or less efficiently to reach by boat (e.g. Barton et al. 1994b). German and Dutch
surveys were initially mainly conducted as part of the international waterfowl census (Bräger 1990), but are
increasingly used to survey marine areas for seabirds and marine mammals (Diederichs et al. 2002). In The
Netherlands, aerial surveys covering the Dutch sector of the North Sea became established as a monitoring
programme conducted by the Dutch government since the mid 1980s (Baptist 1990; Baptist & Wolf 1991, 1993;
Baptist & Meininger 1996).
In Denmark, aerial survey methods were further developed in the late 1980s (Laursen et al. 1997) and
subsequently extended to cover much of the Baltic Sea for wintering seaducks (Durink et al. 1994) and UK waters
(Dean et al. 2003). For these surveys, the methods used varied with species and conditions in the survey areas. In
shallow coastal waters, the coastline was followed 300-500 m from the shore, with supplementary coverage 1.5-2
km offshore. For “total counts” sea areas were defined on the basis of natural ecological, topographical or
geographical units and attempts were made to fly each of these areas in a systematic fashion and assess the total
numbers of birds present (Pihl & Frikke 1992). In the open sea, parallel tracks were flown at regular (2-3 km)
intervals, always ensuring coverage of known reefs and shoals, with reduced efforts at water depths less than 10
m. During these flights, observers registered birds on both sides of the aircraft within 100 m of the observers
(excluding the 10 m on either side directly below the aircraft; Laursen 1997). These strip transect approaches
represented a considerable improvement on the previous methods and exploited the improvements in navigation
aids at that time (notably the new satellite navigation techniques just becoming available).
At present, the Danish protocol as outlined below under “Aerial surveys” (or very similar derivatives) is
deployed in the UK (e.g. JNCC, BTO, WWT), in Denmark and in Germany (BioConsult, FTZ/Univ. Kiel). The Dutch
protocol for aerial surveys is rather different (Baptist & Wolf 1991) and is not recommended in this document.
Seabird at sea survey, Wee Bankie (E Scotland), summer 2003 (CJ Camphuysen)

11
COWRIE research objectives
While the purpose of the present document is to evaluate existing techniques for ship-based and aerial surveys, in
terms of their historical use, demonstrated efficiency, quality, and cost-effectiveness, it was suggested at the start
of the project that research objectives should be made very clear. The following research objectives have been
identified (COWRIE, London, 30 May 2003) and each of the research tools (platforms used, protocols and
techniques deployed) will be evaluated with these goals in mind.
• Seabird distribution patterns
• Seabird abundance
• Migratory pathways
• Foraging areas
• Factors explaining seabird distribution and abundance
• Variability in spatial and temporal patterns
o Seasonal
o Diurnal
o Spatial
• Evaluation of collision risks
The objectives of these large-scale seabirds at sea programmes discussed earlier, partly overlap with the
objectives for specific EIAs in marine coastal areas, but they are different, particularly in scale. For a better
understanding of local areas, fine-scale distribution patterns have to be investigated while the diurnal, spatial and
seasonal variability can only be understood with at least some basic knowledge of the type of birds found
(breeding, transit, wintering, feeding) and underlying determinants of their timing and reason of occurrence in a
given location. It is clearly understood that a full blown ecological study is not what has been asked for (COWRIE
2002). Yet, it is important that census techniques should not be evaluated just on their merits for measuring seabird
abundance and distribution, but be set-up such that our understanding and appreciation of the underlying
mechanisms will be enhanced, preferably at the same cost level. As a simple and straightforward example: where
fisheries enhance foraging opportunities for certain species of seabirds locally and will thus increase seabird
numbers in a given area, measuring trawler activity and the associated seabird movements and congregations
simultaneously will increase our understanding as to how the two interact and how fisheries influence local bird
numbers by providing an artificial food source (discards and offal). Natural variability issues are issues of great
importance and some level of ecological understanding of sea areas is essential if any changes in seabird
distribution and abundance have to be forecasted or evaluated.
It must be stressed here that aerial and ship-based surveys per se are unlikely to provide a complete
answer on all research aims, but some research protocols will provide valuable data. Aerial and boat based studies
of distribution patterns and absolute numbers in a given area, land and “pseudo-stationary” boat studies of
migratory pathways, and collision risks estimated from boat survey data, are unlikely to be all accommodated by a
single research tool, and it should be made clear at the onset of future research what a particular method is most
likely to offer. Other tools will have to be deployed (e.g. radar, heat, impact or motion sensors, etc.) to answer the
numerous questions underlying these topics, but these tools are not addressed in this project.
Observation-techniques should be evaluated for their potential to be used in different conditions such as
visibility (day, night, fog, low cloud), weather circumstances (sea state, rain, ice cover) and water depth
(accessibility of the area for research platforms chosen). The type (technical requirements) of craft and the quality
and training of observers are further issues that need to be addressed.
The research objectives listed above can be lumped into two main categories; one mainly addressing changes in
seabird distribution and seabird abundance (for example through potential habitat loss), the other mainly
considering the risks for collisions (seabirds in flight hitting rotor blades or masts of turbines). As main research
aims, we have summarised and annotated the objectives as follows:
(1) Evaluation of effects of wind farms on seabird distribution and abundance
(2) Evaluation of collision risks (in relation to density, migratory pathways, flying height and weather)
Site-specific knowledge should be obtained prior to any surveys to fine-tune the methodology, including
bathymetry, geographical characteristics, results of previous surveys within the area, likelihood of use by breeding
birds (nearby colonies), by migrants (flyways), by foraging birds (habitat descriptions), by wintering birds or
moulting birds, by fisheries, by marine mammals and the use of the area for mining (platforms, vessels) and by
shipping (traffic lanes).
Patterns in seabird distribution and abundance
The first research aim is based on a more usual set of objectives for offshore surveys and the research protocols
outlined below will produce data that serve our needs. Spatial patterns of seabirds should be studied with a high

12
resolution given the size of planned wind farm sites, the expected variance in seabird presence and usage over the
area and the need to enhance our understanding of underlying mechanisms. Temporal resolution should also be
high, as seabird densities and behaviours, and thus, the risk of collisions or other impacts, may be highly variable
at any one place. Seabird abundance (number of birds per unit area) needs to be assessed with a high accuracy
and with clear confidence intervals. Inter-observer differences should be measured and minimized as much as
possible and corrections should be made for animals missed (distance sampling techniques).
There is a rather large “but”, however, and this has to do with natural variability issues and the use that
may need to be made of reported or forecasted abundance estimates. The reason why wind farm developers
should address seabird distribution issues is that these patterns may be influenced by the building and/or
subsequent operation of a wind farm in a coastal area. These effects may be clear (turbines take physical space
and will trigger avoidance response at least to some extent), or they may be very subtle (enhanced or deteriorating
foraging conditions for certain species). Changed use of an area is notoriously difficult to measure and distribution
patterns are meaningless if explanatory factors are not considered. Distribution patterns should be described in a
context of geographical characteristics (e.g. topography, bathymetry, sediments), oceanographical parameters
(water masses, currents, river outflows etc.), food supplies, and anthropogenic influences (shipping, fisheries).
Many of these data are more or less fixed over geological time-scales or at least many years, others are more
variable and need to be measured simultaneously. As part of the evaluation of ecological mechanisms and factors
underlying distribution patterns, the use of sea areas for foraging and feeding of the respective species should be
examined. Pre-survey studies and survey protocols should accommodate this topic in as much detail as possible.
Evaluation of disturbance and habitat loss
Wind farms that appear in the open sea, will possibly scare birds away from the site. This will lead to disturbance
(birds flying around or over the wind farm) or to habitat loss, through avoidance. At first, habitat loss seems a small
problem, as projected wind farms are small in size compared to the vastness of the sea. However, the number and
size of wind farms will increase rapidly in the future and this may lead to more excessive disturbance or more
extensive habitat loss. This is particularly so, as most European wind farms will be situated in nearshore areas, that
are by nature of a more limited extent than the open sea and that support important migration routes and specific
habitats. Moreover, coastal waters are often relatively important for feeding, breeding, moulting, and migrating
compared to waters further offshore. If many wind farms occur, one after the other along a migration route, the
same birds will need to fly around many more obstacles than just those in the one wind farm that is under study at
any particular time. Likewise, habitat loss will be cumulative for all the wind farms that occur in the same habitat,
such as coastal sites around Britain and Ireland. Such sites are the only habitat (on a national scale) where specific
coastal seabirds, such as divers or seaduck, come to winter in the North Sea. The amount of habitat lost (if any,
this needs to be assessed first) should thus be compared to the total amount of that specific habitat available in the
country, rather than to the total surface area of e.g. the North Sea. If habitats can be described in more detail in
future, habitat loss may prove to be more severe in relative terms than can currently be estimated.
Migratory pathways
Migratory pathways, or intensively used flying routes (including foraging flights to and from breeding colonies) are
not easily described from moving platforms such as aircraft or seagoing vessels. However, a detailed analysis of
directions of flight of seabirds observed with time of day and time of year, and behavioural observations will fill in
some aspects. Detailed studies of migratory pathways require more or less fixed (stationary) platforms of
observation and the use of radar is to be recommended.
Evaluation of collision risks
Birds can only be hit by a rotor when they are flying and even then only when flying at rotor altitudes. As long as
birds are on the water they are not vulnerable. Seabirds fly mostly rather low, below most rotor heights, but they
may reach surprising altitudes on migration (e.g. Bergman & Donner 1971; Bergman 1974; Kerlinger 1982) or
during soaring during the daytime (gannets, gulls). The risk may be assessed as a function of seabird density and
the percentage of time spent in the air, at risky altitudes.
The research techniques evaluated in this document are not designed to evaluate collision risks in great
detail. However, while previous surveys have produced two-dimensional distribution patterns (numbers of birds per
unit area), ship-based survey design could be adjusted such that a 3-D image for at least the lower layers of the
atmosphere (up to a few hundred metres a.s.l.) can be produced. The distribution of flying height can be assessed
during seabirds at sea counts from ships, by categorising any birds seen in flight to its altitude (classes used in
Dutch studies are: 0-2m, 2-10m, 10-25m, 25-50m, 50-100m 100-200m, >200m; a system adopted from landbird
migration monitoring programmes; Lensink et al. 2002). This provides an estimate of seabird numbers in flight per
volume in different weather conditions; information that is very sparse, but important to evaluate seabird numbers
potentially in conflict with moving rotor-blades. This may give a first impression of which birds will be at risk in a
study area. Additional information may be gained from seawatching data (e.g. Krüger & Garthe 2001). As most
collisions will probably take place during the night or during misty, rainy or very windy conditions, when observers
will probably not be able to measure altitudes of flying birds from ships, additional work using radar will be needed
to fully explore this.

13
Natural variability
Seabirds are highly mobile animals, with long-distance migration and dispersion patterns. On top of that, seabirds
may quickly respond to temporarily available food sources, such as discarding fishing vessels, tidally induced
feeding opportunities, food (small fishes) being driven to the surface by underwater predators, etc. Such events
may attract hundreds or even thousands of seabirds to a given spot and if this spot falls into a standard survey, the
resulting enhanced densities greatly affect results. Seabirds at sea studies should therefore incorporate an
evaluation of seasonal patterns, diurnal rhythms, and spatial variability caused by any external factors that can be
identified. For most birds, seasonal patterns are such that areas should be surveyed at least on a monthly basis,
but chosen in response to key moments in the annual cycle of the animals living in the area (wintering, migration,
nesting, fledging, post-fledging care, moult, etc.). An appropriate planning of surveys (survey design) requires a
review of existing knowledge of the animals expected to occur in the area studied. Diurnal patterns and tidal
influences on seabird distribution should be measured and evaluated to allow an appropriate planning of surveys.
Seabird distributions around the British Isles are known mainly in broad terms (e.g. Stone et al. 1995), but
in some parts, e.g. around some colonies, in greater detail (Webb et al. 1985; McSorley et al. 2003). Most
distribution maps that have been produced so far are composites based on data from several survey years. Such
overviews are suitable for determining an average base line situation, but the underlying data need to be re-
analysed for temporal variance. As the ESAS data were not normally collected with a high temporal resolution in
any one place, one will probably find for any particular site, that the data are fragmentary.
Scale and variability
Knowledge of bird densities at a large scale are not generally helpful when addressing more detailed questions
relating to the cause of observed patterns in abundance and distribution, but are crucial to put local findings into
context. Smaller flocks of seaduck and divers may utilise large coastal areas over a short space of time, moving
from one spot to the other and vice versa in response to factors such as weather (exposure), tidal currents and
food supply. Migration corridors can only be understood and described by combining data over large areas and by
effort related observations revealing the often highly peaked seasonal patterns and diurnal rhythms. The usage of
an area by coastal and/or pelagic seabirds and physical boundaries that are of significance to either of these need
attention. It may be so that a physical boundary such as an hydrographical front is just within, or just beyond the
study area, explaining many of the seabird movements and distribution patterns observed. It may also be that
factors outside a study area will control bird numbers within a given study area.
Monitoring seabird numbers in a given area to reveal seasonal or gradual long-term trends or to study the
spatial and temporal variability of seabird numbers in more localised areas in connection to certain environmental
parameters requires a different approach. In these situations, statistical tests between densities in time and space
are a prerequisite of the methods, together with the need for a high level of spatial resolution in localising birds. In
particular, the process of environmental impact assessment, or the identification of geographical boundaries for the
process of site safeguard, requires a high level of spatial precision to describe bird distribution and abundance and
the ability to demonstrate changes in these densities.
Migratory pathways (routes, direction of flight, seasonal patterns).
Seabird movements over the North Sea can be swift or slow and peaks in occurrence may be in the timeframe of a
couple of days or even hours only. Large-scale movements, e.g. from season to season may be inferred from
sequential, monthly or bi-monthly maps that are available for all common species of seabird for large areas of sea
around the British Isles. For instance, the slow migration (by swimming) of Common Guillemots across the North
Sea, between the UK and the Kattegat/Skagerak area may be followed this way. Faster migrations, by birds
moving on the wing will be harder to trace as these may happen within one month, over large distances. Surveys
need to be planned to maximise the likelihood that migrants are actually recorded. Additional information on timing
and direction of flight is available from many coastal, “seawatching” sites around the North Sea. Some information
on seabird movements is available from offshore platforms, that have sometimes been manned by experienced
seawatchers (Camphuysen et al. 1982; Platteeuw et al. 1985).
Weather effects
Seabirds are known to respond to adverse weather by movement, sometimes over large distances. This may lead
to occurrence of offshore species in nearshore waters in connection with specific weather conditions (e.g.
Blomqvist & Peterz 1984) or wrecks (e.g. Camphuysen & Leopold 1996). Obviously, any massive movement of
seabirds may cross a wind farm site and affect densities therein temporarily. Some sites will be more prone to this
than others, and emphasises requirement to survey during all weather conditions which are safe for the survey
platform, not just nice weather! Risk assessments can use meteorological data to predict the likely frequency of
weather events that may increase the potential for collision.
Diurnal patterns and tidal influences
Seabirds respond to offshore foraging conditions in various ways, but daylight and tidal influences are perhaps the
most important factors for many birds to find and obtain prey. Diurnal rhythms may be such that a site is not used at

14
all for some part of the day, with peak occurrences early morning, mid-day or just before sunset. Tidal currents
influence distribution patterns greatly and seabirds may be expected to move in and out sites with the tide. For
migratory seabirds, diurnal patterns in the intensity of migration require attention, for peak occurrences may take
place at certain times of day.
Foraging areas
Specific feeding areas at sea are poorly known. There are obvious concentrations of seabirds at sea around their
colonies, but at larger distances from colonies, or in the non-breeding season, the situation is often less clear.
Predictable feeding concentrations of seabirds and marine mammals are known to occur at frontal systems, around
banks or other elevations on the seafloor, over shellfish banks (seaduck) and around fishing fleets.
Factors explaining seabird distribution and abundance
Seabird distribution and abundance are governed on different time scales. There is a strong seasonal component
that causes a large proportion of any population to be tied to specific areas in the breeding season (e.g. within
flying range of colonies). Many seabirds move to specific areas to moult or winter, following broadly defined
migration routes (offshore species) or more clearly defined narrow migration bands (coastal species). In the short
run, fishing fleets or single fishing vessels will attract scavenging seabirds, but mainly at certain stages of the
fishing process, e.g. when nets are hauled and by-catches and discards are put back into the sea (Camphuysen et
al. 1995). Strong daily rhythms in movements have been observed in wintering offshore seabirds (Camphuysen
1999), while nearshore species such as gulls or cormorants often sleep on land and feed at daytime, at sea.
Hence, abundance of a given species, at a given location at a given time will be a function of total numbers in the
population, the time of year, and possibly the time of day, as well as less predictable factors such as presence of
fishing vessels or approaching weather systems. Many factors need attention when seabird distribution patterns
have to be understood, explained and perhaps even predicted. This includes information on habitat characteristics
(e.g. water mass, geography, depth, distance to land, prey availability) as well as detailed information on the
behaviour (habitat utilisation) of the birds studied.
Common Guillemots with young chicks, just prior to fledging (Farne Islands, summer 2003, CJ Camphuysen)

15
Survey techniques
In an effort to standardise observations, techniques have been developed that provide an index of relative
abundance corrected for observer effort and detection probability and several methods may now be deployed
during ship-based or aerial surveys, including strip-transects, point and line-transect techniques. Direct counts
are very not practical to cover large areas of sea, because animals move, the water moves, the observation
platform moves, and many of the smaller animals are highly inconspicuous or submerged part of the time. Even
with smaller sites, sub-sampling is normally required rather than a direct count of the entire population in the study
area, and the techniques listed above are the most appropriate (Buckland 1982; Buckland & Turnock 1992;
Buckland et al. 1993; Sutherland 1996). Exceptions are direct counts of single, concentrated, large flocks of
seaduck caused by a concentrated resource of food (Offringa & Leopold 1991).
Combinations of methods are possible onboard (large) research vessels, if sufficient numbers of observers
can be accommodated to operate simultaneously and independently. It would be naïve to assume that several
different techniques could be deployed simultaneously by a single observer or by a very small team of (2)
observers without significant loss of quality. Most ESAS associated ship-based surveys and most aerial surveys
have deployed strip- or line-transect counts as the only technique. Within ESAS, much of the ship-based work has
been realised by a single observer. With few exceptions, modern surveys are performed by at least two observers
teamed up to work one transect (four observers if a double transect is worked). Mark-recapture techniques have
thus far seldom been used, but could work with studies of marine mammals.
Line-transect technique using parallel strips (ship and boat surveys)
Line transect versus strip-transect techniques – confusing terminology
It appeared that there is confusion with terms and to avoid further confusion, terms used in this document are
explained here. Ship-based survey techniques for the North Sea have been described as strip-transects (Tasker
et al. 1984). The method required that all birds along the transect are detected within a pre-set perpendicular
distance (the strip width). The strip width needed modification when necessary, i.e. be made narrower during
adverse sighting conditions. As soon as the method was published, it was modified by the main users, to allow
correction factors to be calculated for birds that were missed. To do that, birds seen on the water were ranked in 5
distance categories (A-E); distances perpendicular to the observation platform. The term strip-transect was not
completely abandoned, although the method was now a form of line-transect technique (Komdeur et al. 1992).
Aerial survey techniques, described in this document, have always been described as line-transect counts, even
although the methods used were essentially identical to ESAS ship-based surveys: parallel distance bands as
perpendicular distance groupings of animals observed to allow for later correction of individuals missed at greater
distances. To add to the confusion, line-transect methodology in the strictest sense requires exact measurements
of the perpendicular distance to the track line for every sighting and this method has been used and will have to be
used for marine mammal surveys. While ship-based and aerial seabird surveys group animals in distance bands,
perpendicular distances to the track line are calculated much more precisely by recording angle (°) and distance
(m) for every individual sighting in marine mammal surveys.
The objective of this review is to use a method to generate population density estimates (D) over small areas of the
marine environment based on the most effective sampling methods. One approach to this is to sail or fly extended
transects and describe the distributions of birds encountered by observers along these trajectories, usually in terms
of bird encounters per unit area (e.g. n km
-2
). Strip transect sampling involves travelling along such transects,
counting all the birds encountered out to a predefined distance, effectively covering long linear corridors on either
side of the observer (Buckland et al. 2001). Given k of such strips, each width 2w (w being the width of the area
covered by one observer on either side of the count platform), each strip i has length l
i
, hence the total length (L)
can be denoted:
L = 
k
i=1
l
i
The total number of birds counted in all the strips is n, denoted:
n = 
k
i=1
n
i
Then density D is estimated by:
D = n/2wL
To create a density estimate surface, it would be possible to cut the strips into sections along each transect in order
to define the encounter densities over the study area. However, the basic assumption is that all objects within the
strip are detected. Usually, however, no relevant data are collected at the time of the survey to test this

16
assumption. This assumption is unlikely to be met, unless the strips are restrictively thin, which may in turn be
highly inefficient, since many observed objects would be ignored to ensure all near objects were detected
(Burnham & Anderson 1984).
Line transect (distance) sampling has far greater appeal as a modification of strip transect sampling.
Instead of counting all objects out to a given distance in a strip of defined width, the observer records the distance
of each object from the track line, hence “Distance Sampling” (Buckland et al. 2001). In this way, all objects on or
near the track line are detected, but the method allows for a proportion of the objects present at the time the
observer passes to be missed, within a given distance w. In this case, as long as the observer ensures all objects
on or near the track line are detected, true density can be estimated without bias from the detected objects. An
analysis at species level is required, for species-specific differences exist in detectability.
This makes the method a more efficient use of data gathered by the observer, with large sample sizes for
the same effort, especially when dealing with objects at low density. It also ensures unbiased density estimates,
given that certain assumptions are met. The sampling design requires a number of random track lines, or a grid of
track lines systematically positioned at regular intervals randomly superimposed on the study area. In this case, the
encounter rate within a strip can be thought of in terms of an effective half-strip width of  which represents the
distance from the track line at which as many objects are detected beyond  as are missed within  of the track
line. In this case, density D is estimated by:
D = n/2L
To estimate the effective half-strip width  necessitates the determination of the detection function g(y), i.e. the
probability of detecting an object given its distance y from the track line. This is derived from the population of
object observations generated from the survey results, which will show in simple bi-plots the predictable reduction
in detected objects with increasing distance from track line. In order to generate robust estimates of overall density,
however, the method requires an assessment of g(0) (following the assumption in the model that objects on the
track line are always detected; i.e. that g(0) = 1). In addition, the method also requires that (i) objects are detected
at their initial position, prior to any movement in response to the observer and that (ii) distances to objects are
accurately and consistently determined.
In most surveys, the detection probability decreases with increasing distance from the observer. Although
the nature of the relationship between distance and the probability of detecting an object can vary considerably, it is
relatively simple to model this relationship in such a way as to generate reliable estimates of true density. The
process can also be simplified by “binning” observations. This means that rather than measuring the distance of
every observation from the track line (for example using protractors and triangulation), observers can assign bird
positions to bands of increasing distance from the observation platform. Even using binned data and when small
percentages of the total number of objects are detected away from the track line, modelling offers a highly robust
means of fitting detection functions (Buckland et al. 2001). Although there are a plethora of potential models that
could be fitted to survey data, there is now a body of theory and experience behind such techniques. Furthermore,
the use of likelihood ratio and goodness of fit tests, as well as Akaike’s Information Criterion enables objective
selection between suitable models (Burnham & Anderson 1998).
Such model-fitting provides the most statistically robust method of estimating bird densities over extensive
bodies of open sea based on the results of aerial or ship-based survey, and fulfils all the requirements of the
methods outlined above, as long as the underlying assumptions are met. In particular, the opportunity to generate
estimates with variance precision estimates offers the basis to make comparisons in time and space between bird
densities as are required in the environmental impact assessment method.
Line-transect techniques using individual distances to the track line for marine mammals
This technique, or the true line-transect technique, is most appropriate for recording rare, elusive objects, such as
marine mammals. With the need to carefully assess perpendicular distance from the track line for every individual
or flock observed, this method is not practical to record seabirds at sea, not even in areas with relatively low
densities. Line-transect techniques have been described by Buckland (1985), Buckland & Turnock (1992), and
Borchers et al. (1998).
Point-transect techniques
Strictly speaking, a point transect requires the observer to remain at one point for a fixed period of time to record
the targets at distances recorded in terms of concentric zones around the point (Buckland et al. 1993, Sutherland
1996). For seabirds and marine mammals it is not a very practical method and it hasn't been deployed anywhere,
except on vessels where considerable time was spent on stations. The results will never be very reliable, however,
because the assumption that the behaviour of the animals observed is independent of the observer is almost
always violated: marine mammals and seabirds have a strong tendency to 'check-out' stationary platforms for
foraging opportunities. A variation of the point-transect method has been deployed in a large-scale project where
fishery intensity needed to be measured at the same time as seabirds were counted with the strip-transect method
(Camphuysen et al. 1995). At frequent intervals, all active fishing vessels were counted within a fixed r set on the
radar screen (assumed detection probability = 1). Each snap-shot has geographical information and a known

17
surface area, allowing the calculation of densities (active trawlers km
-2
) and it results in a coarse distribution pattern
of fishing activity. This technique has not and should not be deployed for seabirds or marine mammals at sea.
However, in the specific situation, where seabird densities need to be assessed in a fixed area, such as a
wind farm at sea, the technique may prove useful, specifically when an observation base is present within the park.
Such a base could be a stationary ship (but see above for problems mentioned in relation to such a base). A base,
such as a central ‘command post’ such as a power collection station, equipped with an observation platform, could
prove to be useful, as such a base would be an integral part of the wind farm. Animals being attracted to that base,
or indeed the wind farm, would simply be part of the equation. As such point transect methods have not been used
before properly at sea, and in any case not in a wind farm setting, this is an option that could be explored in the
future.
Seaduck and diver surveys: local modifications to ESAS database
Methodological deviations were sometimes put in place because for example counts of large seaduck or diver
concentrations from ships could not be performed successfully with the strip-transect protocols deployed up until
then (Offringa & Leopold 1991; Offringa 1993; Leopold et al. 1995; Durinck et al. 1993). These modifications meant
that dedicated observers continuously scanned the sea area ahead of the ship with binoculars, to detect the take-
off of usually very wary seaduck and divers well ahead of the approaching platform. Line-transect techniques
(distance sampling) could still be deployed by measuring angles and distances to flushed birds ahead of the ship
(Durinck et al. 1993), but total counts have also been used, e.g. on very large (tens of thousands) groups of
seaduck.
Geographical accuracy
The advent and wide availability of navigation aids (such as global positioning systems [GPS]) enable the
identification of the precise position of a moving observer with accuracy. This enables pilots and skippers to
establish waypoints and fly or sail along predetermined track lines with a very high degree of accuracy. Such
equipment also enables surveyors to localise observations of individual birds, or flocks of birds, with similar
accuracy. This means that, rather than smoothed or amalgamated sampled densities over grid squares, the
surveyor can plot with an increasing degree of spatial accuracy all encounters with birds. This has a number of
immediate benefits, which need to be considered, and taken advantage of, in designing any survey protocol. Not
least of these benefits is that the observational unit becomes a flock or individual bird (aerial survey) or a number of
records within a short time interval (ship survey) with a precise location, rather than a pooled average density. This
enhances the opportunity to relate bird distributions to oceanographic, bathymetric or other physical/biological
features of their environment that could influence their distribution and which could potentially contribute to
modelling distribution and abundance in time and space. It should be stressed immediately that to appropriately
relate the distribution of birds to oceanographic (and most biological) features, such data should be collected
simultaneously.
Because the mapping of individual birds and groups of birds can be very precise, with accumulated
knowledge and appropriate replication of survey, the variations in abundance and distribution of seabirds can be
defined in such a way as to define spatial and temporal patterns in abundance and distribution. In particular, such
detailed mapping of flocks and individuals will demonstrate with considerable confidence where and when seabirds
consistently occur, where they occur less frequently and areas where their occurrence is rare. Using even a very
simple GIS platform, this would immediately enable the zoning of potentially damaging operations in time and
space that would minimise any potential effects on seabirds given a composite overview of annual changes in their
distribution in a given area. The ability to provide these data with some statistical rigour based on individual
positions provides an important tool to zone areas of importance for seabirds as well as define those areas where
the birds almost never occur.
Red-throated Divers in flight, Iceland, summer 2001 (CJ Camphuysen)

18
Ship-based seabird surveys
Strip- and line-transect techniques for seabirds
The standard strip-transect techniques used by the European Seabirds at Sea Database group (ESAS) have been
outlined by Tasker et al. (1984). Modifications have been described by Komdeur et al. (1992), and what was called
strip-transect technique thus far is basically identical to what is described as line-transect technique in the
description of aerial surveys (see inset above under “Survey techniques”). The method involves a 300m wide band-
or strip-transect operated on one side and ahead of the ship and short time-intervals (1, 5, or 10-minute periods) in
a continuous series to sample short stretches of water with a known surface area, a known location and any other
biological, geographical, or physical factors that could be associated by that area. To evaluate the bias caused by
specific differences in detection probability with distance away from the observer, the transect is subdivided into
narrower distance strata (A= 0-50m away from the ship, B = 50-100m, C = 100-200m, D = 200-300m, and E >
300m). A species-specific frequency distribution over these strata would indicate how many individuals were likely
to have been missed in the furthest strata (Distance Sampling). All birds on water within 300m perpendicular to
trackline of the ship are counted as 'in transect'. To avoid an overestimate of bird numbers in flight, a regular
snapshot of flying birds over the transect and within 300m distance ahead of the ship is performed (frequency of
snapshots depending on ship’s speed; Tasker et al. 1984). Distance techniques, used to correct numbers of birds
observed swimming to numbers believed to have been present on the water, cannot be deployed on birds in flight.
Birds 'outside transect' are recorded either in a 90° or 180° scan ahead of the ship. Birds recorded in the scan are
not used to calculate densities, and recording them has therefore a lower priority than recording birds in transect
when abundance estimates are the main objective of a survey. Scan results may enhance assessments of age-
and sex composition of certain populations or directions of flight by migrants and birds travelling to and from
colonies simply by enlarging sample sizes and the scan accommodates sightings of rarer, highly mobile seabirds
such as shearwaters, skuas, terns and migratory birds that would otherwise remain unrecorded, or flushed birds,
e.g. divers and scoters.
Transect width is 300m by default, unless circumstances (sea state, visibility, small ship size) prevent the observers
from doing so. However, it is recommended to discontinue systematic surveys in circumstances so poor that a
minimum width of 200m cannot be maintained. Time-intervals deployed are variable, in response to specific needs.
Tasker et al. (1984) proposed 10-minute intervals. Large-scale surveys are indeed usually performed with 10-
minute intervals, but smaller scale surveys should be conducted with 5-minute or 1-minute intervals. For the
preferred vessels and speeds deployed (see below), working on gradients over miles rather than tens or hundreds
of miles, we would propose 5-minute intervals as a sensible default, 1-minute intervals for a more detailed
approach. At a ship groundspeed of 10 knots (nautical miles per hour) a single 5-minute count would comprise an
area of 1543 m x 300 m = 463,000 m² (50/60 of a nautical mile length, 300m width), whilst a 1-minute count would
comprise an area of 309 m x 300 m = 92,650 m² (10/60 of a nautical mile length, 300m width). Each snapshot
captures ± 300 m x 300 m = 90,000 m². For each time-interval a central geographical position (lat-long) is stored
into the database. In most situations, this requires accurate logging of start- and end-positions, and a calculation of
mid-positions afterwards.
Efficiency may be enhanced by operating two transects at the same time, one on each side of the ship. This will
require extra observers, but no extra ship time. Sun-glare is a problem to take into account, as now both sides as
opposed to the side with optimal light and sighting conditions need to be operated. Therefore, operating one
transect (best side) is preferred over operating two transects for which usually one has much poorer light
conditions. An advantage of operating two transects at the same time is, that with more surface area surveyed per
count, chances of recording “false zero’s” decrease, and more accurate assessments of low densities may be
achieved. Small-scale differences in seabird densities may also be better assessed this way.
The method assumes that target species behave independently of the observers/the observation platform.
Therefore, ship-followers should not be recorded as animals in transect and in fact should be kept aside at all
times. To avoid problems with ship-followers it is important to maintain a minimum speed of the platform (> 5
knots). At low speed, ship-followers have a stronger tendency to fly ahead of the vessel. Strip transect counts are
excellent for counting seabirds at sea and the method does not require a random distribution of target animals to
be successful. A careful assessment of distances (at least within the 300m boundary should be carefully set and
maintained) is essential to avoid over-or under-estimations.
Following the demands to evaluate sea areas in a context of offshore wind farm developments, the methods have
been evaluated again and new modules were attached to the standard methods by a number of (independent)
researchers around the North Sea (Exo et al. 2003; Garthe et al. 2003; Hüppop et al. 2003). It is these newly
proposed modules plus the original methods for ship-based and aerial surveys at sea that are evaluated in the
present study, to set standards for future work around the UK, and hopefully elsewhere in Europe.

19
Transect set-up recommendations for ship-based surveys
Time intervals
1
Band width Subdivision Observers Snap-shot
Minimum 1 min 200m A (0-50m)
B (50-100m)
C (100-200m)
D (>200m)
2 200m
Maximum 10 min 300m A (0-50m)
B (50-100m)
C (100-200m)
D (200-300m)
E (>300m)
- 500m
Recommended
1
5 min 300m A (0-50m)
B (50-100m)
C (100-200m)
D (200-300m)
E (>300m)
 2 300m
1
Scale dependent, 5-min intervals produce valuable data on the gradient level of several nautical miles, 10-min counts may be more useful at
larger scales, 1-minute counts are preferred and recommended when a high level of accuracy is required in very small study areas or for
example in combination with hydrographical observations. Note that (total) band width, as well as the number of observers double if two strip
transects are to be operated simultaneously.
Behaviour of birds
A protocol has been provided to record behavioural aspects of the birds observed (Annex 1). Crucial are attempts
to relate the presence of birds to any visible cues in the area (e.g. fishing vessels, front lines, floating matter,
offshore installations, marine mammals) and to try and distinguish between birds that simply pass through an area
(e.g. migrants, long-distance feeding flights) and birds that utilise a site for feeding, resting, or other activities. A
careful recording of directions of flight, particularly in nearshore situations, will enhance the understanding of
seabird movements in an area. Today’s practice is to record flight directions in octants (1 = no direction, 2 =
northward, 3 = NE, 4 = E, 5 = SE, etc; ESAS Database protocol, see Annex 1).
Flying height of birds
The distribution of flying height can be assessed during seabirds at sea counts from ships, by categorising any
birds seen in flight to its altitude (classes used in Dutch studies are: 0-2m, 2-10m, 10-25m, 25-50m, 50-100m 100-
200m, >200m; a system adopted from landbird migration monitoring programmes; Lensink et al. 2002). This
provides an estimate of seabird numbers in flight per volume in different weather conditions; this is important when
evaluating seabird numbers potentially in conflict with moving rotor-blades.
Training of observers, observer quality
A presumably large, but often neglected source of variation is inter-observer differences (van der Meer &
Camphuysen 1996). Observers on board must be competent. Specifically, they must be well-trained both in terms
of their identification skills as well as in their capacity to deploy the required survey technique (especially to record
navigational data and deploy the snapshot technique for flying birds), and observers must have good eye-sight and
be able to withstand rough seas and overcome sea-sickness. To become a competent observer, several boat trips
under contrasting situations are required, normally involving several weeks of fieldwork under the supervision of a
very experienced observer. Within ESAS, observers from different teams (internationally) are encouraged to try to
organise joint cruises to be able to compare their work directly and to detect differences in interpretation of the
prescribed methodology. Employing only experienced observers and frequent training will solve part of the problem
of individual variation, but this source of variation (negative bias mostly) will in all likelihood be greatly reduced (no
specific studies have been carried out on this topic), by using more than one observer to watch the same transect.
Therefore, as recommend earlier, two observers should be employed on each side of the ship.
Avoiding attraction by birds
Vessels at sea attract seabirds, even if they do not provide food. As a default, attracted birds (normally defined as
those remaining with the ship for more than 2 minutes) should be coded as such and kept out of the analysis of
densities in an area. From commercial fishing vessels, sensible data on seabird distribution at sea cannot be

20
obtained and working on fisheries research vessels is only feasible if fishing operations are wide apart and
separated by prolonged sessions of full-speed steaming. It is strongly recommended not to use fishing vessels for
offshore surveys that have accurate abundance estimates as a prime objective.
Additional data
Ship-surveys provide unique opportunities to obtain additional data. Vessels equipped with an Aquaflow could
record characteristics of the surface water, such as temperature, fluorescence (chlorophyll), and salinity
simultaneously with the bird counts. Water depth (depth sounder) and the presence of fish (acoustic survey) are
further sets of data that will enhance the understanding of area usage by marine birds.
Recommended methodology, ship-type, and observers
Recommended census techniques for ship-based seabird surveys, as part of an EIA, are line-transects with sub-
bands and with snap-shots for flying birds, and incorporating the full behaviour module recording detailed
information on species, sex and age where feasible, foraging behaviour, flying height. Whenever possible,
hydrographical data, such as sea surface temperature, salinity, water depth should be continuously and
synoptically monitored. For a minimum set-up, the following techniques and qualifications are recommended.
Line-transect methodology is recommended with a strip width of 300m maximum.
Subdivision of survey bands to allow corrections for missed individuals at greater distances away from the
observation platform (recommended subdivision for swimming birds: A= 0-50m, B= 50-100m, C=100- 200m, D=
200-300m, E= 300+m or outside transect; all distances perpendicular to the ship).
No observations in sea state 5 or more to be used in data analysis for seabirds, data not usable for marine
mammals above sea state 3.
Survey time intervals are recommended to be 5 (1) min intervals (range 1-10m, longer time intervals are
acceptable when less resolution of data is required), with mid-positions (Latitude, Longitude) to be recorded or
calculated for each interval.
Preferred ship's speed should be 10 knots (range 5-15 knots).
Preferred ship type is a motor vessel with forward viewing height possibilities at 10m above sea level (range 5-
25m), not being a commercial or frequently active fishing vessel.
Preferred ship-size: stable platform, at least 20m total length, max. 100m total length
Bird detection by naked eye as a default, except in areas with wintering divers Gaviidae. Scanning ahead with
binoculars is necessary, for example to detect flushed divers.
Two competent observers are required per observation platform equipped with range-finders (Heinemann
1981), GPS and data sheets; no immediate computerising of data during surveys to maximise attention on the
actual detection, identification and recording.
Observers should have adequate identification skills (i.e. all relevant scarce and common marine species well
known, some knowledge of rarities, full understanding of plumages and moults).
Observers must be trained by experienced offshore ornithologists under contrasting situations and in different
seasons.
A high resolution grid should be deployed, covering an area at least 6x the size of the proposed wind farm
area, including at least 1-2 similar sized reference areas (same geographical, oceanographical characteristics), and
preferably including nearby coastal waters (for nearshore wind farms only).
Survey grid lines are recommended to be at least 0.5nm apart, maximum 2nm apart, and the grid should be
surveyed such that time of day is equally distributed over the entire area (changing start and end time over the area
to fully comprehend effects of diurnal rhythms in the area)
The cost-effectiveness of the ship-based surveys are greatly enhanced if the vessel can be equipped with an
Aquaflow (logging surface water characteristics including temperature, fluorescence (chlorophyll), and salinity
logging hydrographical information simultaneously).
The cost-effectiveness of the ship-based bird surveys can be greatly enhanced if combined with other surveys,
such as those of marine mammals, for which a specialist observer and different methods will be required.
The cost-effectiveness can be further enhanced by counting birds on both sides of the ship, i.e. cover two
strips, for which additional observers will be required.
Conclusions
In attempting to draw together the various conclusions relating to the effectiveness of ship-based surveys, and in
particular the approaches presented here, it is important to reconsider the objectives set for the method. These are
summarised in Table 1.
Explaining seabird distribution in ecological terms is not just a scientific interest, but is essential to
understand seabird occurrences from census data, to explain the (natural) variability of the data collected, or even

21
to predict (future) occurrences (Maurer 2002; Scott et al. 2002). Ships work more slowly than aircraft, and therefore
spend longer at sea. Whilst this may seem a disadvantage at first glance, seagoing vessels may offer better
possibilities to record natural variability issues, such as tidal and diurnal patterns in seabird abundance resulting
from shifts and patterns in area usage. Directions of flight and the (ecologically relevant) behaviour of seabirds can
be studied in considerable detail, while (foraging) associations with for example fisheries, marine mammals, and
oceanographical phenomena can be logged in great detail. These data enhance the possibilities for an ecological
interpretation of the material collected and, hence, will be essential to evaluate the area studied for migrants,
residents, (nearby) breeding birds, and winter visitors.
The cumulative distribution of encounters of individuals of given species can provide inference on foraging
areas, but without detailed investigations of prey distributions, foraging behaviour and the conditions enhancing the
availability of prey to foraging seabirds, there will be no difference with for example results from aerial surveys. The
great benefit of ship-based surveys is the potential to collect data on foraging conditions (water masses, presence
of prey) simultaneously (oceanography, acoustic survey, fisheries data) or near-simultaneously (benthic sampling)
with foraging seabirds. In addition and in general terms, the incorporation of environmental covariates into spatial
and temporal models to generate bird density surfaces can provide insight into the factors affecting birds
abundance and distribution. The possibility to exclude non-residents (migrants) or non-foraging seabirds from
actively searching and feeding seabirds will strengthen the analysis and will help with the interpretation of results.
As a contribution in the evaluation of collision risks, ship-based survey protocols can be easily modified as
to collect data on the height of flight under different conditions. A three dimensional pattern of seabird distribution
and abundance will result. Still, static measuring devices (such as infra-red movement triggered video surveillance
and vibration detection equipment currently under development) are needed to measure the impact of windfarms
more directly.
Table 1. Overview of effectiveness of ship-based strip-transect surveys, distance sampling, spatial and temporal
modelling techniques in relation to specific tasks set under the process of environmental impact assessment of
offshore windfarm development.
Strip
transects
Distance
sampling (line-
transect)
Spatial
modelling
Temporal
modelling
Other
approaches
needed
Seabird
distribution
Good Better Best Best Validation
(double platform
or other)
Seabird
abundance
Good Better Best Best Validation
(double platform
or other)
Migration routes Reasonable No improvement Better Better
Migration flight
Direction
Good No improvement Better Better
Seasonal
migration
Good No improvement Better Better Combine with
data collected at
coastal sites
(seawatching)
Weather effects Reasonable Better Best Best
Foraging areas Best No improvement Best Best
Factors affecting
distribution and
abundance,
diurnal patterns
and tidal
influences
Best No improvement Best Best Foraging
associations
recorded,
oceanographical
data directly
coupled
Prediction of
collision risk
Information of
height of flight
collected
No improvement No improvement No improvement 3D radar studies
of flight
trajectories
before/during/po
st- construction
Assessment of
collision risk
No
contribution No contribution No contribution No contribution Infra-red video;
vibration
detectors post-
construction
Assessment of
disturbance and
habitat loss
Good Better Best Best

22
Aerial seabird surveys
One of the objectives is to achieve the mapping of bird density distributions at the highest possible spatial
precision, without causing disturbance to the underlying pattern of distribution, and while using analytical
techniques that derive workable precision estimates about density estimates. The techniques reviewed, presented
and recommended in Komdeur et al. (1992) were developed for the general description of bird numbers and
distribution in offshore waters on a macro scale. This type of approach was used with success to analyse numbers
and distribution at flyway, regional and national scales (such as those presented by Durink et al. 1994, Pihl &
Laursen 1996, Laursen et al. 1997). However, these methods were never developed to generate fine scale density
estimates of smaller areas of open sea, nor were the data they generated of a form that could support the use of
analytical tools that would enable statistical comparisons of time series. Such analysis is fundamental, for example,
in a situation where it is necessary to compare before, during and after seabird distributions during the construction
of an offshore windmill park. This chapter concentrates upon the rationale behind the adoption of best-practice
aerial survey techniques, with reference where appropriate to other techniques.
This part of the desk study is less of a review of aerial surveys than a justification of the methods adopted
by the National Environmental Research Institute (NERI) in Denmark, simply because of the scarcity of information
relating to different techniques. Wherever possible, some justification for the methods adopted are offered where
there are appropriate experiences in the literature, but all too often there is little published to offer guidance on the
best techniques available.
Transect bands
Experience suggests that assigning sample unit observations to one of three transect bands in the time available to
process and record the information seems to be as much as can be dealt with under normal circumstances. Sub-
division into further bands does provide benefits, especially with regard to generating density estimates for distance
sampling. However, it is recommended that any further subdivision of bands is done on the basis of distances
which equate to declination angle units of 5° or 10° apart to greatly aid the speed involved in checking distances
using the inclinometer. It is also essential that any such further subdivision is carefully considered and subject to
trials in the field, given that it must still be possible to assign all observations to these bands even at greatest rates
of encounter. It is suggested that transect bands are identified by alphabetic codes to avoid confusion with flock
numbers or registrations of time intervals.
Using the NERI system and the Partenavia P-68 observer aircraft (see below), transect bands A, B and C
(defined below) are covered on both sides of the aircraft. Use of the inclinometer, to measure vertical declination
from the horizontal (i.e. 0°) is encouraged at all times, to enable the observer to confirm the correct categorisation
of birds or flocks in the correct transect bands. This method has been found to be better than using tape or
striations on the bubble windows of survey aircraft or other methods such as wire tracers mounted externally (e.g.
on wing struts see Figure 7.9 on p.261 of Buckland et al. 2001). The latter techniques necessitate flying without roll
or yaw and protracted periods where the observers do not move their head relative to the markers. All data
gathering assumes that there is a “dead angle” underneath the aircraft that the seated observers cannot cover,
here considered to be an angle greater than 60° from the horizontal. Given a normal flight altitude of 250 feet
(80m), the transect bands are defined as follows:
Band Boundary distances (in m.)
perpendicular out from track line
Declination in degrees from the
horizontal
A 44-163 60-25
B 164-432 25-10
C 433-1000 10-4
Time is read from the watch, which is preferably attached to the window of the plane in an appropriate position to
allow the observer unhindered access to read the time whenever necessary. It is only necessary to record minutes
and seconds, recording the hour only when changing from one to the next. It is, of course, essential that the
stopwatches be synchronised with the GPS used. Time should be recorded as often as practically possible. It may
become necessary to pool more than one observation of birds under the same time record. The guiding principal
should be that the more frequent the time recordings are, the greater the accuracy obtained in the final analysis.
The position assigned to each observation is made under the assumption that the time is recorded at the
precise moment the observation passes abeam of the aircraft on the transect strip. This is normally the case, but if
for reasons of observation density, recordings are made where this assumption is not met, and birds are recorded
at times after the point of encounter, this fact should be noted on the tape.
Choice of airframe
One major prerequisite for the suitability of a particular aerial platform is that the aircraft flies at a speed slow
enough to enable the onboard observers to count and identify birds over the widest area possible. In general terms,
this means normal operational flying speeds of 250 km h
-1
, and preferably less. With their ability to fly slower,

23
helicopters offer the opportunity to fly transects at a greater range of speeds than fixed wing platforms. Whilst the
cruising speed for most small helicopters at sea level is around 200 km h
-1
(e.g. 230 km h
-1
for an Aerospatiale SA
330 Puma, 200 km h
-1
for a Bell 212, and 167 km h
-1
for an Aerospatiale SA 318 C Alouette-Astazou), operational
direct line flight speeds can be reduced yet further without compromise to safety. Unfortunately, a second major
prerequisite on the method of data collection is the major assumption of many aerial survey methods is that birds
are first detected by the observer in a distribution that is undisturbed. Helicopters are associated with intense noise,
both high and low frequency, which is detectable at long distance and tends to be highly disruptive to waterfowl
generally (Miller 1991, Mosbech & Glahder 1991, Holm 1997). Although habituation is known to occur under certain
circumstances (Kahlert et al 1996, Holm 1997), this is unlikely to occur in the case of occasional surveys over large
areas of marine waters. This disturbance of the detected distribution from the “natural” distribution creates
considerable difficulties for the accuracy and precision of population estimates. Although attempts have been made
to correct for the overestimation in numbers that invariably results, in practice, it is extremely difficult to calibrate for
the disruption caused by the aircraft (e.g. Linklater & Cameron 2002).
Microlight aircraft also offer low survey speeds for wildlife surveys (e.g. Murn et al. 2002), but the
combination of low speed and noise is also highly disruptive, the platform lacks necessary endurance and the
associated safety hazards of operations at sea rule this out with regard to aerial survey for offshore wind farm
developments. Safety and aircraft endurance is also a constraint on airframe – although a Piper Cub has a
potential cruising speed of 110 km h
-1
, normal fuel tanks and loading only offer an endurance of 4 hours. This
greatly restricts operations and the safety margin, especially with regard to diversions in the case of engine or other
mechanical failure. The same restrictions apply to most single-engine aircraft, and flight safety rules in Europe
effectively restrict operations in the offshore zone to twin-engine aeroplanes. For this reason, surveys in most
western European countries have increasingly been carried out using twin-engine aircraft, most commonly high-
wing aircraft that ensures best all round visibility for observers. Extensive experience has been obtained in
Denmark in seabird surveys conducted from a high winged, twin-engine Partenavia P-68 Observer, designed for
general reconnaissance purposes. Although other aircraft would undoubtedly be suitable for the purpose, the
bubble windows in the side of this aircraft and the Plexiglas nose of this particular type make this aircraft eminently
suitable for the task of aerial survey (see Figure 1). JNCC has been using a normal Partenavia P-68 (e.g. Dean et
al. 2003) around the UK.
Figure 1. Partenavia P-68 Observer aircraft. Note the plexiglass nose for pilot and front seat observer, and bubble
windows on both sides of the aircraft in the rear passenger panels (see on open door to right).

24
Survey flight speed and altitude
The question of the appropriate flight speed and altitude is an intractable one to some extent, representing as it
does a compromise between competing requirements placed on sampling. Flight speed is set to some degree by
the nature of the aircraft, which is in turn determined by factors other than survey protocol (e.g. safety and
endurance). Extensive previous experience with aerial survey, aircraft availability, high wing design, bubble and
Plexiglas windows all confirmed the Partenavia as the natural choice for this work in Danish waters, but other
factors may conspire in favour of other aircraft under other conditions. Optimal speed is a trade off between
visibility and the time needed for adequate observation and rapid passage over birds sitting on the sea. Whilst
there is therefore no good reason for flight speed to be set at 185 km h
-1
, subsequent experience has shown this to
be a suitable level in terms of operational expediency and the ability of observers to record observations in good
time. Following the results of test flights in the Kattegat in August 1999, flight altitude during surveys was
standardised at 80m at a cruising speed of 185km h
-1
(Kahlert et al. 2000). This enables rapid approach to birds
sitting on the sea, causing minimal disturbance, since the aircraft is over and to some extent beyond birds sitting on
the sea before many react. Flying similar tracklines with the same aircraft at 150m dispersed birds at up to 2 km
distance ahead of the plane, especially displacing birds into flight along the transect line. Since a fundamental
assumption of the distance sampling technique is that birds are detected before or at the moment they react to the
approaching plane, this makes 80m much more suitable than higher altitudes above the water surface for counting
seabirds. There is no doubt that the optimal flight height is likely to vary with species and it is unlikely that there is a
perfect combination of flight speed and altitude that offers best opportunities to survey all seabird species, but the
experience of several years now is that this platform is as good as any alternative. There is no doubt that this issue
would merit further experimentation to verify the best possible techniques, but it is important to maintain survey
conditions as constant as possible under the circumstances. In reality, the use of distance sampling offers a robust
method for estimation of bird densities, such that even if very small proportions of the numbers of a particular
species present are detected (but critically including all on the trackline), the “loss” of observations resulting from
flying “too” fast makes little difference to the precision of the estimates generated.
Data collection and observer training
During surveys, two observers, one covering each side of the aircraft, record all observations continuously on
dictaphone, giving information on species, number, behaviour, transect band and time. Concentration needs to be
maintained over extended periods of flying, and observers need to be able to maintain vigilance and avoid
becoming drowsy. Prior to a survey, new observers must be introduced to technical equipment such as GPS, the
PCs and the software used, dictaphones, inclinometers, stopwatches, etc and become proficient with their use, so
that reactions become automatic. All observers require training in the recording routines, and new observers will
need easy access to a graphic copy of recording protocol during flight, covering the methods for recording birds as
well as human activities and environmental variables. There is no time during data collection for discussions about
how to handle data or undertake unfamiliar tasks. Species identification of birds from an aircraft is a skill unfamiliar
to most ornithologists and can take some time to acquire. Although observers must naturally have a good basic
ornithological experience, particularly with coastal waterbirds, even the best observers need some guidance with
specific identification difficulties involved with the unfamiliar experience of birds viewed from above.
Estimating the numbers of individuals in flocks is a challenge that many observers will be familiar with
beforehand. However, these skills need honing in situations where flocks are viewed from above, often under
unfavourable viewing conditions. Computer count simulation programmes can greatly assist observers to check
their ability to estimate flock size. After each survey, the performance of inexperienced observers needs to be
assessed. Species identification is one particular issue that should be checked against the other observations on
track, but also an observer’s ability to designate observations in the correct transect bands, using the inclinometer
to check judged distances, should be evaluated. New observers must be taken along on a survey with the sole aim
of training and getting used to count conditions. Komdeur et al. 1992 suggested that it takes 150–200 hours of
flying to become proficient in using aerial survey methods. We suggest this is unnecessarily demanding to be set
as a standard for new aerial surveyors and suggest a minimum of 30 hours flying time, depending on individual
skills, would be sufficient for most observers, accompanied and assessed by an experienced, qualified surveyor.
Spatial precision and recording protocols
The objective is to gain the maximum possible precision in recording the position of birds or groups of birds in the
open sea. This is achieved using a Global Positioning System (GPS), recording the precise position of the counting
observers if necessary every second. This enables the establishment of a relationship between bird observations
and a time sequence, which can then be used to relate a single observation to a precise position in time and space.
Pre-planned transect end points may be entered into the aircraft GPS as waypoints used in the navigation of the
aircraft along the transect tracks.
Birds are assigned to three transect bands each side of the aircraft by use of an inclinometer, used to
determine angles below the horizon, measured abeam from the flight direction of the aircraft. Beneath the
Partenavia P-68 observer aircraft, a band 44 m wide on either side of the flight track cannot be seen by seated
observers and should therefore be excluded from analysis. For other planes, this dead angle needs to be carefully
assessed. Bird observations are assigned to transect bands based upon their distance from the track line beneath

25
the plane and for the Partenavia P-68 observer aircraft as: 44-163 m (band A), 164-432 m (band B) and 433-1000
m (band C). To be able to incorporate differential detectability in the analysis of results from aerial surveys, the
response of observed birds to the aircraft were assigned to the categories: sitting (on the water), diving, flushing or
flying. During aerial surveys, a computer logs latitude, longitude and time from a GPS (preferably differential
GPS) at five-second intervals. The accuracy of GPS longitude and latitudinal must be about 10 metres. After the
completion of a survey, tables of observation/count data and flight track data have to be created from the
transcription of the dictaphone tapes. In situations where high densities of birds are encountered, some
observations may have a common time reference. Grouping of observations should not extend over a period of
more than 10 seconds, to keep overall positional accuracy within c. 250m of actual, but could potentially in cases of
grouped observations, for 10 seconds extend to 500m.
Data format
Throughout survey flights, all observations should be recorded onto a dictaphone tape. Each tape could start with
information on type and call sign of aircraft, survey area identifier, date, observers, etc. for future reference.
General details of the weather conditions, visibility, sea state should be reported onto tapes and then modified as
often as this changes after the initial definition. The start of the flight along each transect line should be identified by
recording the precise time at which each waypoint was passed, followed by the records of birds along its length,
concluding with time at which the aircraft completed the transect. Any changes in observation conditions should be
recorded between transects. Ideally, every observation record should contain the following data: species, numbers,
response behaviour (i.e. in flight, flushed, swimming or diving), transect band, and time to the nearest second.
Species
All waterbirds should be recorded and in cases where identification to species is not possible they should be
recorded to the best level of accurate identification, i.e. “small gull”, “small diver”, “auk”, etc. Under this general
heading, all human activities in offshore waters should be recorded as well. These observations may contribute to
the patterns of observed bird distributions, and therefore offer a simple, but often effective variable that contributes
to modelling avian distribution patterns. These observations could include static features, such as gill net markers,
gas platforms, etc., which are indicators of human activity as well as more conventional moving vessels such as
fishing boats, ships, ferries, wind-surfers, etc. Observations of marine mammals should be recorded too, preferably
with a measure of the vertical angle to the animal abeam of the track line. However, all ancillary observations and
records of this nature should only be recorded if there is no cost to the accuracy or precision of recording the
primary species for which the survey was designed.
The unit sampled is either a single bird or a group of birds, insofar as all other information relates to this
sample unit. In situations where a small discrete group of birds straddles one or more transect bands (see below)
observations should be assigned to the transect band in which the mid-point of the flock is situated. In the case of
species such as eider and common scoter, large aggregations of birds may occur over extensive areas with no
discernible flock structure (as viewed from the point of view of the observer in the aircraft). In this case, the flock
should be separated and assigned into the three transect bands as if they were separate sample units (even
though they may represent members of one flock "unit" when seen at a greater spatial scale). As far as possible,
observations should not be amalgamated into larger units before they are recorded on the Dictaphone, since it is
important to try as far as possible to retain the most fine-grained spatial scale when recording each sample unit.
It is inevitable that the survey aircraft will displace some birds. Furthermore, the response of individual birds to
the aircraft has a considerable effect on the detectability of the individual. Since distance sampling makes the
assumption that birds are undisturbed at the point at which they are first detected, it is important that if the need
arises, it is possible to carry out analysis on data that exclude, for example, birds flushed or flying. For this reason,
all records of birds should have information on response behaviour, and under the normal protocol, four different
responses are recognised and recorded: sitting, diving, flushing, and flying. In order to maintain the rhythm of
observations, it is essential that these behaviours are recorded for every observation. When transcribed, these
behaviours are converted to a numeric code for analysis (see below).
Constraints on counting conditions
Survey results are highly sensitive to weather conditions. Surveys should not start when wind speed exceeds 6 m/s
when detectability of birds is severely reduced. High wind speeds create greater sea surface featuring (e.g. white
wave tops, greater shadowing), which means that observers are more likely to fail to see birds than under more
optimal conditions. This becomes critical for the survey when observers are unable to detect all birds in the closest
transect band to the aircraft. At regular intervals (and at least at the start of every transect line) sea state and an
assessment of light conditions (glare) should be recorded. Additional recordings should be made whenever
conditions change along the transect line. All recordings should be followed by a time recorded from the watch.
Sea state describes the sea surface conditions from mirror calm (0 Bft), through tiny ripples (1), small
waves (2; no whitecaps), small waves (3; with few whitecaps), moderate waves (4; numerous whitecaps), larger
waves with whitecaps forming bands (5), and large waves with dominant whitecaps forming broad bands (6). At
sea states above 3, there is no point in undertaking surveys, the data quality will be poor. Glare is recorded as the
angle of the sun to the flight direction, with a subjective assessment of intensity (i.e. low, moderate or high). The

26
times at which encountered bouts of precipitation started and stopped should also be recorded, as these may
impede visibility.
Observers should also record the times when land (including sand and mud exposed at low tide) is
encountered within the transect bands (start and stop times).
Current methods of data presentation and analysis
The objective with current research programmes at NERI is to develop spatial modelling tools that enable the
construction of continuous density estimate surfaces for single bird species over large areas of shallow sea. These
surfaces will be of a suitable geographical resolution that enables a comparison of densities present before, during
and after the construction of a windmill farm in the study area. Specifically, differences in the density estimates
generated will (in combination with associated statistical precision) enable the calculation of the avoidance effect,
not just within the confines, but also around the periphery of the wind farm to the distance dictated by the
behavioural responses of the species concerned.
However, until these techniques are fully available, it is difficult to convert the aerial counts into estimates
of bird density in any sub-sections of the study area, because of the detection probability functions associated with
the counts at the time of the flights. For this reason, and because different sea areas are covered in different
survey flights, to date, bird numbers have been presented in the form of birds encountered per unit km surveyed, or
as total numbers encountered during a survey (see for example Kahlert et al. 2000). The high level precision
achieved with the positions of all observations gives confidence in using this sample of actual observations to be
used to interpret the overall distribution of birds in the general area. In particular, the encounter rate (i.e. the
numbers of birds counted per unit length of transect effort) offers a robust interim measure of the relative densities
of birds and their distribution throughout a count area.
Potential future developments
Double Platform
Further development along a number of lines of enquiry could be continued, particularly with respect to estimating
detection probability using the methods of Borchers et al. (1998). The double-platform analysis methods can allow
effective strip width to be estimated as a function of any number of covariates without the traditional line-transect
assumption that all organisms in the observers’ path are detected. There remains much scope for further
development of such techniques to look in depth at factors affecting effective strip width. While glare from the sun
and sea states can greatly affect visibility and have a dramatic effect on effective strip width, an effort to quantify
this important variable has to be made, for example by analysing the results with the sun intensity and sea state as
quoted in categories during the surveys. Using the GIS platform we can calculate the angle between the individual
observer’s core search angle relative to the angle of the sun, and thus get a value of the search condition in the
transect bands.
Spatial modelling
Great advances have been made in developing statistical techniques that permit seabird density to be modelled as
smooth functions of space, time and other variables, using the data gathered continuously along transect lines. The
first phase has involved the identification of areas of consistently high seabird density, but the next challenge is to
incorporate a temporal element to determine whether such patches of high density persist over time, i.e.
incorporating inter- and intra-annual (i.e. inter-seasonal) effects into the modelled distributions. Further
development should incorporate human activity as a source of deviance in the model from distributions predicted
by the environmental covariates.
Recommended methodology, airframe characteristics, and observers
For a minimum set-up, the following techniques and qualifications are recommended.
 Twin-engine aircraft (for safety and endurance)
 High-wing aircraft with excellent all round visibility for observers (e.g. twin-engine Partenavia P-68)
 Line-transect methodology is recommended with sub-bands.
 Transects should be a minimum of 2 km apart to avoid double-counting whilst allowing the densest
coverage feasible
 Flight speed preferably 185 km h
-1
at 80 m altitude
 Subdivision of survey bands to allow calculations of detection probabilities (recommended are 44-163m,
164-432m, 433-1000m, with a declination in degrees from the horizon being 60-25°, 25-10°, and 10-4°
respectively for the Partenavia P-68 at 80m)
 Use of an inclinometer to measure declination from the horizon
 Two trained observers, one covering each side of the aircraft, with all observations recorded continuously
on dictaphone

27
 GPS positions are recorded at least every 5 seconds (computer logs flight track)
 The time of each bird sighting should be recorded, ideally to the nearest second, but within 10 seconds
accuracy, using a watch attached to the window of the plane.
 No observations in sea states above 3 (small waves with few whitecaps)
 All waterbirds should be recorded to the best level of identification (species or group)
 Sampling units are single birds or groups of birds within the three transect bands
Conclusion
In attempting to draw together the various conclusions relating to the effectiveness of aerial surveys, and in
particular the approaches presented here, it is important to reconsider the objectives set for the method. These are
summarised for convenience in Table 2.
Advantages/disadvantages of using an aircraft as a platform for bird surveys in open offshore areas can be
summarised under different headings. The speed of aircraft guarantees a rapid, simultaneous coverage of large
areas, to provide a snapshot of distribution and density. A disadvantage of this is that due to short observation time
there will be identification problems, reduced count accuracy, and loss of species. In addition, there is little time for
supplementary observations (sex, age, behaviour, etc.). With the flying height of aircraft, a good perspective over
an extensive area is provided, and an extended detectability gradient. The downside is that there is no additional
information on biological, hydrographic or other environmental parameters collected simultaneously, although GPS
registrations enable subsequent analysis of bird distributions in relation to such parameters obtained by other
methods. The use of skilled observers and constant methods are essential for reliable data collection, just as with
ship-based surveys, and so require trained, competent observers and suitable aircraft. In stable weather
conditions, aerial surveys can rapidly cover huge areas. Surveys are highly weather dependent (high cloud, good
visibility) and extended bad weather is highly disruptive. An advantage of the use of aircraft is that a switch
between different study areas in event of poor weather in one or other can be made with relative ease. Aircraft are
relatively cheap per unit area covered, but expensive overall if extensive coverage is required.
Aircraft are able to survey for most seabird species without causing excessive disturbance, at least prior to
the arrival of the aircraft. This is not the case for ships which may disturb red-throated divers and common scoters
at considerable distance ahead of the vessel, necessitating extensive use of binoculars to permit detection and
some compromise of the survey methods.
The acquisition of information about migration routes, direction or height of flight, detailed spatial and
temporal distribution require intensive radar and direct observation in the vicinity of a proposed wind farm
development to determine bird use of the area and to predict collision impact probabilities under a range of differing
temporal (day/night) and weather conditions. Similarly, assessment of actual collision risk and collisions after
construction necessitates static measuring devices (such as infra-red movement triggered video surveillance and
vibration detection equipment currently under development). Aerial platforms are not, therefore, appropriate for
these aspects of wind farm EIA.
The cumulative distribution of encounters of individuals of given species can provide inference on foraging
areas, but without detailed investigations of prey distributions and availability to foraging seabirds, the technique
requires more detailed studies to confirm predator-prey interactions. Similarly, in general terms, the incorporation of
environmental covariates into spatial and temporal models to generate bird density surfaces can improve model
output and give insight into the factors affecting birds abundance and distribution, but it requires detailed ecological
investigations to determine ultimate factors affecting bird distributions.
Aircraft offer great possibilities for adequate surveys in shallow areas or in waters with subsurface reefs
and sandbanks, where seagoing research vessels are hindered or have no access at all. Aerial surveys are
essentially very fast (high speed) and therefore relatively cheap, compared to ship-surveys, for covering relatively
large sea areas.
Table 2. Overview of effectiveness of aerial transect methods, distance sampling, spatial and temporal modelling
techniques in relation to specific tasks set under the process of environmental impact assessment of offshore
windfarm development.
Aerial
transects
Distance
sampling
Spatial
modelling
Temporal
modelling
Other approaches
needed
Seabird
distribution
Good Better Best Best Validation (double
platform or other)
Seabird
abundance
Good Better Best Best Validation (double
platform or other)
Migration routes Poor No
improvement No
improvement No improvement 3D Radar

28
Aerial
transects
Distance
sampling
Spatial
modelling
Temporal
modelling
Other approaches
needed
Migration flight
Direction
Poor No
improvement No
improvement No improvement 3D Radar
Seasonal
migration
Poor No
improvement No
improvement No improvement 3D Radar
Weather effects Reasonable Better Best Best 3D Radar
Foraging areas Reasonable Better Best Best 3D Radar
Factors affecting
distribution and
abundance,
diurnal patterns
and tidal
influences
Reasonable
in conjunction
with other
data
Better Better Better Extensive research
linking food
availability and
predation risk
(including
disturbance)
Prediction of
collision risk
No
contribution No
contribution No
contribution No contribution 3D radar studies of
flight trajectories
before/during/post-
construction
Assessment of
collision risk
No
contribution No
contribution No
contribution No contribution Infra-red video;
vibration detectors
post-construction
Assessment of
disturbance and
habitat loss
Good Better Best Best
Northern Gannet in flight, Wee Bankie area, summer 2003 (CJ Camphuysen)

29
Transect sampling design
Systematically arranged parallel transect lines
There are considerable advantages to the systematic coverage of open water habitats. Such featureless open
water is naturally characterised by a range of physical and environmental factors that are likely to influence the
abundance and distribution of the birds, but about which little can be inferred from the surface without taking
measurements. A sampling approach that covers large areas of such habitat could be constructed on a random
basis, but this process often results in clumping of transect lines which may actually bias the data collection.
Preferentially, the sampling design should comprise a grid of systematically spaced line transects, randomly placed
within the study area. Such a series of parallel lines has logistic advantages, in the sense that the ends of each
transect can be entered into the GPS as a series of waypoints, travelled (sailed or flown) in succession across the
study area, with relatively short turning and transit between the end of successive lines.
Grid orientation
The most statistically efficient study design is a set of line transects running perpendicular to major environmental
axes. In the case of survey for coastal seabirds, which tend to sort themselves according to food availability and
water depth, the dominant environmental gradients are those running perpendicular to the shore (i.e. increasing
depth out to sea). For this reason, it usually makes sense to plan the transects to run to and from the coastline out
into deeper water. Using a set of line transects parallel to the coast may result in considerable sampling bias
(contra: Baptist & Wolf 1991; 1993). However, in areas where deep estuarine channels extend out from the coast,
the most significant environmental gradients may not be oriented parallel to the coast. Careful planning of transects
is necessary, using charts and other suitable information sources, in order to reduce variance between transects.
Transect intervals
In any analysis, such as distance sampling, the sampling unit is a single transect, not individual observations.
Hence, there should be enough transects in each study area to generate confident estimates of numbers. Although
it is impossible to define “how many is enough” without an extensive pilot study, ideally there should be around 20
transects in each separate study area. The other constraint upon line transect spacing is the distance to which
seabirds are displaced, and hence the extent to which substantial double counting could occur. It is assumed that
transects at less than 1 km intervals will run a high risk of double counting, while intervals of 2 and 3 km will reduce
this risk.
Diurnal variation
Diurnal patterns in seabird behaviour (e.g. foraging activity, tendency to roost, migration intensity) are prominent in
most species, with important consequences for spatial patterns measured in relatively small areas. Transects
should therefore be sampled such that peak occurrences are unlikely to be missed and this requires site-specific
reviews of existing knowledge and a design of transects flown or sailed that doesn’t just include the most suitable
time of day for researchers, ship’s crews and pilots, but does take diurnal patterns in the study objects (seabirds at
sea) into account.

30
Seabird behaviour
The behaviour of seabirds, where properly understood, gives vital information on the use that the animals make of
the area surveyed. Foraging, feeding, and roosting or resting seabirds utilise an area in a radically different way
than passage migrants and distribution patterns can be explained in terms of area utilisation based on behaviour
aspects rather than on plain densities. Behaviour can only be observed from rather slow-moving observation
platforms such as ships, while aerial surveys are not expected to produce significant results. A comprehensive
protocol for behaviour recording and subsequent computer coding has been adopted by ESAS in recent years
(Camphuysen & Garthe 2001). Annex 1 lists the codes currently in use by NIOZ; for a full description of the
rationale and an explanation of the codes see the publication mentioned at:
http://wwwold.nioz.nl/en/deps/mee/projects/impress/publications.htm
The behaviour recording protocol is implemented without actually changing the core ship-based survey methods,
so that historical data (abundance and distribution) can still be combined or compared with more recent surveys.
Actively foraging Northern Gannets, North Sea, summer 2003 (photo C.J. Camphuysen)

31
Conclusions
Using spatial and temporal modelling techniques to estimate bird density over certain areas of open sea offers the
best method for statistically detecting differences in the distribution and abundance of these birds before, during
and post-construction of offshore wind farms. The advantage of using distance sampling to estimate bird densities
based on bird surveys in open offshore areas is that it is a reasonably simple method which enables an estimation
of bird densities incorporating covariates (such as light conditions, sea state, observers) in detection probabilities,
with high precision and with confidence intervals to permit comparisons. The use of distance sampling and spatial
modelling enables the use of environmental covariates to generate population estimates with greatly improved
precision. Hence, the method is also robust as a means of deriving factors explaining seabird distribution and
abundance. When the line-transect methods are deployed as described in this document, both aerial and ship-
based surveys provide the data required. The main differences between aerial and ship-based surveys are:
(1) Accuracy for species identification (lower with aerial surveys, higher with ship-based surveys)
(2) Time needed to survey large area (shorter with aircraft, longer with ship-based surveys)
(3) Access to shallow sea areas (potentially unlimited for aircraft, restricted for vessels)
(4) Disturbance of some inshore species, such as Red-throated Divers and Common Scoter (less with
aerial surveys, higher with ship-based surveys).
Consequent and accurate recordings of flight directions, height and flocking behaviour will provide insight
to migratory pathways and for example colony movements associated with colony location. This is feasible only
from ships. It should be realised that the precise mapping of migratory pathways will require considerable amounts
of data, and that a more prolonged stay within the study area will result in more robust data. Consequent and
accurate recordings of bird behaviour will provide essential insight in the ways of utilisation of an area by the
respective species (e.g. as a feeding ground, as a stop-over during migration, as a roosting site, on transit only)
and this is important information before, during and post-construction of offshore wind farms.
Delegates at the COWRIE workshop, held in Aberdeen, November 2003, were asked to compare the
strengths and weaknesses of aerial and ship-based surveys, for application in offshore wind farm EIAs.
It was agreed that, having reached some agreement on the recommended methodologies to be employed for both
platforms, there was little point in comparing the accuracy of the two approaches. The meeting was in agreement
that the use of the two platforms was complementary, in so far as ship- and aerial-based counts fulfilled different
objectives. Hence, these were not an “either-or” option, but rather tools to be used to obtain different forms of data
to inform the EIA process. For this reason it was agreed that a matrix was to be produced which attempts to
develop further the simple strengths and weaknesses associated with each method provided in the main document
(see above). In this matrix, the relative strengths and weaknesses of the recommended boat and aircraft count
platforms has been summarised to achieve specific objectives likely to arise from the needs of EIAs.
The first tier of EIA necessitates collation of year-round baseline information for the proposed wind farm area and a
larger contextual area, such as the UK strategic areas for wind energy development, (e.g. literature search,
preliminary exploration of existing ESAS and seawatching data, evaluation of colony information and waterfowl
censuses in the area), and baseline aerial and/or ship-based surveys, to determine spatial and temporal
occurrence of birds in the area. Ideally, the baseline data will inform the next stage of the EIA process and the
objectives of any further investigation. For example, surveys may identify offshore concentrations of terns, but
explain nothing of the breeding colonies from which they originate. Such information requires a deeper level of
investigation, at which point it becomes necessary to evaluate the two different platforms in order to fully assess
their relative suitability to meet the specific goals of the more detailed investigations.
Rather than offer a set of prescriptions, or a decision tree, it was decided to provide a tabulation of the relative
ability of aerial or ship-based counts to meet certain objectives likely to arise in an EIA. In Table 3, we list as many
survey and/or monitoring objectives arising from EIA casework as we have been able to accumulate from our
present experience. Table 3 aims to provide a clear objective, with an associated score (ranging from * for survey
platform fulfils the objective to a limited degree, to *** for the best ability to fulfil the objective. These scores are
based, where possible, on published sources and demonstrated ability of either platform to provide the necessary
information. Footnotes have been provided as appropriate where clarifications or caveats are required for each
objective.

32
Table 3. Survey and/or monitoring objectives arising from Environmental Impact Assessment casework and the
suitability of aircraft or ships for offshore surveys.
S
URVEY
/M
ONITORING OBJECTIVE
A
IRCRAFT
S
HIP
1. Physical features relating to survey area
Cover complex,low coastlines, skerries *** *
Cover shallow water
*** *
1
Survey extensive areas of open water *** ***
Survey restricted areas of open water *
2
***
Survey distant offshore waters * ***
3
2. Complementary data, other than bird abundance and distribution
Achieve instantaneous gathering of complimentary oceanographic data (e.g.
temperature, salinity profiles, fish distributions, etc.) during bird surveys *
4
***
5
Define seabird flight lines (e.g. commuter routes between colonies and feeding
grounds) * **
Describe migration routes/pathways * **
7
Age/sex determination * ***
Behavioural observations (Annex 2) *
6
***
Describe diurnal, tidal and other ephemeral patterns in bird distributions **
8
Describe feeding patterns * ***
Define foraging areas * ***
3. Logistic and other constraints
Avoid time/tide constraints ** *
Intensive coverage of small areas *
2
***
Simultaneous coverage over large areas *** *
Ability to take advantage of short spell of good weather conditions ** *
4. Species surveys – distribution and abundance (demonstrated ability; published sources)
Survey diver abundance (Gavia spp.) *** **
Survey grebe abundance (Podiceps spp.) ** **
Survey Fulmar *** ***
Survey shearwaters *** ***
Survey storm-petrels * ***
Survey Gannet *** ***
Survey seaduck *** **
Survey gulls *** **
Survey terns ** ***
Survey auks ** ***
Migrant species of other groups *
7
5. Species groupings – identification to species (* = most unidentified, *** = nearly 100% identified)
Identify divers to species ** ***
Identify grebes to species * ***
Identify auks to species * ***
Differentiate Velvet Scoter and Common Scoter ** ***
Differentiate Lesser-black-backed and Great Black-backed Gulls * ***
Differentiate Herring and Common Gulls ** ***
6. Other subjects relating to contributions to EIA
Evaluation of collision risk
9 9
Predicting collision risk
9
*
1In waters less than 5-10 m, vessel draft can restrict access of boats, so special, flat-bottomed vessels may be required
2Aircraft less suitable on grounds of cost-benefit
3Less efficient for extensive areas and long transit movement
4Only using modelled or remotely sensed data
5Assuming suitable on-board equipment and expertise
6Only at the level of flying/diving/swimming/flushing
7Radar techniques more appropriate than either platform
8Still requires radar or infra-red/light intensifier equipment to gather night time data (radar could be implemented on ship if
stabilised)
9Neither platform offers any basis for recording collisions and population damage resulting from this, both identify some of the
species most prevalent (and therefore most at risk) in the immediate area, a flying height recording protocol on board vessels
will provide information on birds that are particularly sensitive.

33
Acknowledgements
This project has benefited from the critical input of a large number of people and we wish to acknowledge them all.
Joining our discussions in the Aberdeen workshop were: Alex Banks (BTO), Colin Barton (Cork Ecology), Jenny
Bell (Central Science Laboratory), Phil Bloor (DTW Oil and Gas Office), Charlotte Boesen (ENERGI E2 (DK)),
David Borchers (St Andrews University), Kees Camphuysen (Royal NIOZ (NL)), Caoimhe Cawley (Coveney
Wildlife Consulting Ltd.), Andrew Clarke (Ocean Marine Research Limited), John Coveney (Coveney Wildlife
Consulting Ltd.), Anne Marie Coyle (Powergen), Peter Cranswick (WWT), Ben Dean (JNCC), Ansgar Diederichs
(BioConsult SH (FRG)), Allan Drewitt (English Nature), Jonathan Ford (Independent consultant), Tony Fox (NERI
(DK)), Jette Gaarde (Elsam Engineering (DK)), Mick Green (Ocean Marine Research Limited), Colette Hall (WWT),
Carolyn Heeps (Crown Estate), Mike Kaiser (School of Ocean Sciences), Rowena Langston (RSPB), Genevieve
Leaper (Independent consultant), Rick Lockwood (Ocean Marine Research Limited), Lucas Mander (Institute of
Estuarine and Coastal Studies IECS), Steve Percival (Ecology Consulting), Ib Crag Petersen (NERI (DK)), Werner
Piper (BIOLA (FRG)), Claire Pollock (Cork Ecology), Jim Reid (JNCC), Garry Riddoch (Environmentally
Sustainable Systems), David Sales (Environmentally Sustainable Systems), David Simmons (Department Of Trade
and Industry), Lucy Smith (WWT), Mark L. Tasker (JNCC), Dieter Todeskino (IBL Umweltplanung (FRG)), Andy
Webb (JNCC), Kathy Wood (AMEC Wind Energy), Kevin O'Carroll (DTI). Written comments have been received
from Paul Gill and D.I. Sales (Environmentally Sustainable Systems), Dieter Todeskino (IBL Umweltplanung), Sian
Whitehead (Cyngor Cefn Gwlad Cymru), and M.J.M. Poot, S. Dirksen & R. Lensink (Bureau Waardenburg).
Rowena Langston was instrumental, particularly in later phases of the project, by collecting and processing
comments provided by Sarah Wood (CCW), Allan Drewitt (English Nature), Zoe Crutchfield, Mark Tasker and Andy
Webb (JNCC) and draft-reading on behalf of COWRIE.
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36
Annex 1
Recording seabird behaviour (applicable for ship-based surveys only)
A protocol has been provided to record behavioural aspects of the birds observed. Crucial are attempts to relate
the presence of birds to any visible cues in the area (See “ Associations and direction of flight”), e.g. fishing
vessels, front lines, floating matter, offshore installations, or marine mammals and to try and distinguish between
birds that simply pass through an area (e.g. migrants, long-distance feeding flights) and birds that utilise a site for
feeding, resting, or other activities. A careful recording of directions of flight, particularly in nearshore situations, will
enhance the understanding of seabird movements in an area.
Behaviour codes Behaviour
Associations and direction of flight
30
Holding fish Foraging 1
Flying, no apparent direction Direction of flight
31
Without fish
2
Heading N
32
Feeding young at sea
3
Heading NE
33
Feeding, method unspecified
4
Heading E
34
Wading, filtering or probing
5
Heading SE
35
Scooping prey from surface
6
Heading S
36
Aerial pursuit
7
Heading SW
37
Skimming
8
Heading W
38
Hydroplaning
9
Heading NW
39
Pattering
10
Associated with fish shoal Associations
40
Scavenging
11
Associated with cetaceans
41
Scavenging at fishing vessel
12
Associated with front
42
Dipping
13
Associated with line in sea
43
Surface seizing
14
Sitting on or near floating wood
44
Surface pecking
15
Associated with floating litter
45
Deep plunging
16
Associated with oil slick
46
Shallow plunging
17
Associated with floating seaweed
47
Pursuit plunging
18
Associated with observation base
48
Pursuit diving, or bottom feeding
19
Sitting on observation base
49
Actively searching
20
Deliberately approaching observ. base
60
Resting or apparently asleep General 21
Associated with other vessel
61
Coursthip display
22
Associated with or on buoy
62
Courtship feeding
23
Associated with offshore platform
63
Copulating
24
Sitting on offshore platform
64
Carrying nest material
25
Sitting on marking pole or stick
65
Guarding chick
26
Associated with fishing vessel
66
Preening or bathing
27
Associated with or on sea ice
67
[still free for future use]
28
Associated with land (e.g. colony)
68
[still free for future use]
29
Associated with sand banks
69
[still free for future use]
50
MSFA participant, no further details MSFAs
70
Wheeling or swimming slowly Cetaceans 51
MSFA participant, joined by others
71
Escape from ship (rooster tail)
52
MSFA participant, joining flock
72
Swimming fast, not avoiding ship
53
MSFA participant, scrounger type
73
Breaching clear out of the water
54
MSFA participant, solitary diver
74
At the bow of the ship
55
MSFA participant, beater
75
Apparently feeding: herding behaviour
56
MSFA participant, social feeder
76
Apparently feeding: other behaviour
57
Type II MSFA participant
77
Calf at the tail of adult
58
Type III MSFA participant
78
Calf swimming freely in herd
59
[still free for future use]
79
Basking, afloat
80
Spy-hopping
81
Lob-tailing
82
Tail/flipper slapping
83
Approaching ship
84
Only blow visible (whales)
85
Only splashes visible (dolphins)
86
Acrobatic leaps
87
Sexual behaviour
88
Play
89
Sailing
90
Under attack by kleptoparasite Misfortune, disease
91
Under attack (as prey) by bird
92
Under attack (as prey) by mar. mammal
93
[still free for future use]
94
[still free for future use]
95
[still free for future use]
96
Entangled in fishing gear or rope
97
Oiled
98
Sick, unwell
99
Dead

37
Collection behavioural data
(1) Direction of flight (codes 1-9) The rationale behind records of direction of flight is that (sea-)birds move from A
to B on purpose. Searching (foraging) birds may seem to move more or less randomly over the sea. Birds coded
with a direction of flight must have a distance code 'F' by default, while marine mammals travelling about may
combine a 'direction of flight' code with an indicator of swimming ('A'-'E' or 'W') by default. Nine codes are reserved
for direction of flight, including 1 (no apparent direction) and 2-9 (octagon, N  NW). For specific areas, such as
while recording seabird movements near colonies (flying to and fro), directions of flight may be of great interest (cf.
Schneider et al. 1990; Camphuysen et al. 1995).
(2) Associations (codes 10-29) Fairly often, we can actually see where the birds are heading for, or why they are
on a given spot: for example a feeding frenzy, a fishing vessel, or the breeding colony. In those cases, it is of
greater significance to code their goal (association) rather than their direction of flight. Therefore, within the same
database field, and with priority over direction of flight, codes for 'associations' of seabirds with certain surface
phenomena are proposed.
Association codes have been devised for birds associating with near-surface fish shoals or marine
mammals, with floating objects such as wood, rubbish, oil slicks, or sea weeds, with fronts in sea (often indicated
by distinct lines separating two water masses or concentrations of flotsam), with the own observation base (by
default not in transect), with buoys, markers, other vessels, offshore installations, sea-ice or with land. A group of
birds flying towards a distant fishing vessel can now be coded as flying with a F under distance, and as associated
with fishing vessel with code '26'. The behaviour field (see below) should now be left blank, to separate the
approaching birds from actual scavengers around the ship, either 'searching' for prey, actually feeding, or perhaps
resting near the ship (see behaviour codes below). Similar combinations can be made for e.g. birds flying towards
land, or birds flying in association with or towards a front, overruling the 'direction of flight' code that would not have
been particularly informative.
(3) Foraging behaviour (codes 30-49) Types of foraging behaviour were characterised following Ashmole (1971),
but with some modifications such as the split use of 'scavenging' for birds feeding at fishing vessels and birds
scavenging on a corpse, plus a distinction between 'surface seizing' (few, large prey) and 'surface pecking' (many,
tiny prey). For use in shallow seas, 'wading' (and filtering or probing for prey) and 'scooping' (as in pelicans) were
added. Contrary to Ashmole, there is no separation between wing- and feet-propelled diving, because we do not
want to code what we cannot actually see. One of the most interesting aspects of test-cruises was, that certain
seabirds did not always feed the way they should have done typically according to text books, but may change
feeding techniques in particular situations. An approaching ship will trigger escape reactions of seabirds on the
track line. Aerial species may simply fly off, but pursuit diving species such as auks may dive to escape from the
vessel. It is up to the observer to discriminate between 'feeding dives' (code 48) and 'escape dives' (no code), but
in case of doubt we recommend to refrain from coding. Of particular interest is the coding of 'searching' seabirds
(code 49). The idea is, that seabirds actually 'foraging' (looking for prey) in a given area can be separated from
those that are just there, even although the latter might use a sudden feeding opportunity. Potential feeding areas
don't necessarily show off by the presence of actively feeding seabirds; prey density may for example be low or
prey may be difficult to detect. Although any migrating seabird may interrupt swift flight to pick up a prey
encountered by coincidence, any observer familiar with birds at sea will agree on the concept of separating actively
searching individuals from birds that simply move about. Searching albatrosses and petrels circle consistently over
certain patches (Veit & Prince 1997), with the head constantly pointing down or sideways. Searching Northern
Gannets and terns may follow straight lines, but while peering down constantly. Shearwaters may settle and alight
repeatedly, moving apparently randomly over an area, constantly reacting on one another. Auks extensively peer
under water (they may do that also when disturbed by a ship, perhaps as a check of a route to flee). Gulls circle
and hover repeatedly during their searches, skuas looking for options to kleptoparasitise 'stalk' and fly low before
preparing their attacks. All those (and more examples) can be coded with 49, but it does not harm to make
additional notes on paper for future reference.
(4) Complicated associations: multi-species (foraging) assemblages (codes 50-59) All birds, whether
swimming or flying, that operate 'together' or stay tight in a particular area or in a particular movement are marked
as distinct 'flocks'. Flocks comprising more than one species are called 'multi-species (feeding) associations'
(MSFA's). Recent studies have shed some light on composition, structure and dynamics of MSFAs of seabirds
(Sealy 1973; Hoffman et al. 1981; Porter & Sealy 1982; Maniscalco 1997), and on the specific role of different
species in mixed-species assemblages (Bayer 1983; Grover & Olla 1983; Chilton & Sealy 1987; Hunt et al. 1988;
Mahon et al. 1992; Camphuysen & Webb 1999; Ostrand 1999). MSFA's may be formed around fishing vessels
(scavenging seabirds), in association with cetaceans and around sources of more natural prey (fish, plankton,
carrion). Many MSFA's are formed by surface feeding or shallow plunging seabirds over concentrations of prey
driven to the surface by underwater predators (predatory fish, cetaceans, seals or seabirds). Current knowledge
suggests that these flocks represent an important behavioural mechanism in the exploitation of resources of food
that are ‘normally’ out of reach for surface feeding seabirds. There is a great demand for additional observations

38
and quantifications, which we might fill in by careful descriptions and systematic coding of what can be seen at sea
during routine cruises.
Camphuysen & Webb (1999) evaluated the available literature and terms and categorisations of the role of
seabirds (or marine mammals) in multi-species feeding associations. Important categories are (1) initiators or
producers (birds that actually start the feeding frenzy by locating a food patch), (2) joiners or scroungers (birds
streaming into patches discovered by others) and (3) divers or beaters (often the triggers of MSFA formation). To
categorise a bird correctly according to their system, individuals need to be followed and watched for some time,
sparsely available in standard cruises. Prior knowledge of existing group structures and (potential) dominance
hierarchies might help in understanding and recognising what is going on (See Camphuysen & Webb 1999, and
Camphuysen & Garthe 2001 for further details).
(5) General behaviour (60-69) Besides foraging, seabirds can engage in a variety of other activities that one may
wish to record. Particularly nocturnal feeders may sleep a lot during the day, while birds that have just joined a
feeding frenzy often rest on water, incapable as they even may be to fly away (code 60). Mostly during spring,
seabirds frequently perform courtship displays at sea (code 61), including courtship feeding (62), copulation (63;
e.g. Atlantic Puffins Fratercula arctica), the handling of nest material (64), or chick guarding (65). Other coded
activities include preening and bathing (66).
(6) Marine mammals (codes 70-89) Most seabird observers under ESAS record marine mammals, perhaps as a
matter of lower priority but still, as if they were birds. To facilitate a rapid description of observed behaviour, we
propose 20 behaviour codes that would suit most needs.
(7) Misfortune, disease and death (codes 90-99) Ten codes are reserved for 'birds under stress', including
deceased individuals. Entangled, oiled, otherwise 'sick' or even dead animals may be encountered in places and
seabirds under attack by other animals can be coded with the system provided below.
Height of flight Additional database field can be reserved to record the flying during seabirds at sea counts from
ships, by categorising any birds seen in flight to its altitude. Classes used may be (from Lensink et al. 2002):
0-2m very low over the water
2-10m undulating flight or just below the horizon (with observer eye-height at c. 10 m asl)
10-25m at or just above the horizon
25-50m well above the horizon*
50-100m flying high*
100-200m flying very high*
>200m great height*
*Requires pre-survey training for example on land with reference heights in the landscape.
Recording prey
Finally, as one of the most difficult tasks at sea, it may be possible to recognize prey caught or targeted by seabirds
at sea. The ultimate record does not only include place, species, age and plumage, but also association, behaviour,
and prey (and all that preferably within transect). Prey data are stored in a separate column in the birds file under
ESAS and several of a potential of 100 codes (0-99) are attributed to various prey, summarised as follows: Fish
prey (10) fish, no further details, (11) small fish, unidentified (ca. bill length), (12) medium fish, unidentified (ca. 2-
5x bill length), (13) large fish, unidentified, difficult to handle, (14) sandeel ball, (15) clupeoid ball, (16) unidentified
fish ball, or (17) capelin ball at surface, (20) gurnard, (21) herring or sprat, (22) sandeel, (23) gadoid fish, (24)
flatfish, (25) regurgitated fish after aerial pursuit, (26) salmonid, (27) capelin; Miscellaneous prey (30) small
particles, unidentified, (31) large object, unidentified, (32) jellyfish, (33) squid, (34) worm (e.g. Nereis), (40)
crustacean, unidentified, (41) swimming crab, (42) starfish, (43) sea urchin, (45) bivalve, unidentified, (46) mussel;
Carrion and corpses (50) carrion or big corpse, unidentified, (51) seal carcass, (52) whale carcass, (53) bird
carcass, (54) litter, rubbish, (55) regurgitated unidentified prey after aerial pursuit, (56) bird kill (e.g. Bonxie), (57)
excrements (e.g. from whales); Discards and offal (60) fishery waste, unidentified, (61) discarded roundfish, (62)
discarded flatfish, (63) discarded offal, (64) discarded benthic invertebrate, (65) discarded starfish, (66) discarded
crustacean (e.g. shrimp)