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130 © British Birds 112 • March 2019 • 130 – 145
Population estimates
of wintering waterbirds
in Great Britain
Teresa Frost, Graham Austin, Richard Hearn,
Stephen McAvoy, Anna Robinson, David Stroud,
Ian Woodward and Simon Wotton
Richard Allen
Abstract This paper provides updated estimates of population size for wintering
waterbirds in Great Britain using recent data and new analytical approaches for
some species that use smaller inland waterbodies or the non-estuarine coast. These
population estimates provide crucial baseline information that underpins the
implementation of international conservation obligations, including the
identification of wetlands of national importance. Overwinter population estimates
are presented for 98 species or populations, including seven non-native populations
and, for the first time, estimates for Cattle Egret Bubulcus ibis, G los sy Ib is Plegadis
falcinellus and Sandwich Tern Thalasseus sandvicensis. In addition, January-only
population estimates are presented for the first time for 48 species or populations
in order to support international population monitoring. There is an urgent need
for a process to collate marine waterbird survey data, which currently is being
collected commercially but remains unavailable for national syntheses.
Common Shelducks Tadorna tadorna and Eurasian Teals Anas crecca at Wallasea, Essex
Introduction
Great Britain is important as a wintering area
for millions of migratory waterbirds and has
international treaty obligations to protect
them, including the EU Birds Directive, the
Ramsar Convention on Wetlands, and the
Agreement on the Conservation of African-
Eurasian Migratory Waterbirds. To protect
them effectively, it is critical to collate the
best available evidence on population sizes
and trends to provide context for conserva-
tion decision-making. Trends in overwin-
tering populations are published annually by
the BTO/RSPB/JNCC Wetland Bird Survey
(WeBS) (Frost et al. 2018) and here we
update estimates of population size last pub-
lished by Musgrove et al. (2011) using data
from WeBS, the Goose and Swan Monitoring
Programme (GSMP), the Non-estuarine
Wa te rb ir d S ur ve y (N EW S I II ), th e W in te r
Gull Roost Survey (WinGS), county bird
reports and other sources. This update largely
follows the methods used by Musgrove et al.
(2011), and any changes are outlined below;
further background information can be
found in that paper.
Scope
This assessment considers waterbird species
or populations that regularly occur in winter
in Great Britain, including non-native species
that are on the British List with self-sustain ing
populations (BOU 2017). Here, ‘waterbird’
follows closely the definition used in
Waterfowl Population Estimates (Wetlands
International 2018). This includes species of
geese, swans and ducks (Anatidae), divers
(Gaviidae), grebes (Podicipedidae), ibises and
spoonbills (Threskiornithidae), herons
(Ardeidae), cormorants (Phalacrocoracidae),
rails (Rallidae), cranes (Gruidae), waders
(Haematopodidae/Recurvirostridae/
Charad ri idae/Scolopacidae), gulls and terns
(Laridae). Auks (Alcidae) are not included
here, as the species in this family do not make
extensive use of British inshore waters in
winter and are poorly monitored.
The geographical scope of Great Britain in
this assessment includes England, Scotland,
Wales and offshore islands, but excludes the
Isle of Man and the Channel Islands.
Estimates for Northern Ireland are consid-
ered alongside the Republic of Ireland; the
131British Birds 112 • March 2019 • 130 –145
Population estimates of wintering waterbirds
85. Pink-footed Geese Anser brachyrhynchus, Norfolk, October 2018. Pink-footed Goose is the
most numerous goose in Great Britain, wintering mainly in eastern and southern Scotland,
northern England and East Anglia. The population continues to rise steadily and has now
surpassed half a million birds, with an average over 2015/16 and 2016/17 of 510,000.
Richard Chandler
latest estimates will be published by Burke et
al. (in press).
Previous assessments of wintering water-
bird population estimates in Great Britain
(Musgrove et al. 2011 and earlier) were pre-
sented as national estimates for the whole of
Great Britain but it is now clear that these
estimates were likely to have more accurately
reflected just terrestrial and inshore popula-
tions. In recent years, the increase of indus-
trial and other activities in the UK’s marine
waters has required regulatory assessments.
The resulting surveys have found that, for
some waterbird species, significant numbers
occur during the non-breeding season in
marine waters. In this update of population
estimates, published surveys and estimates
from marine waters have been incorporated
where possible, but it has not been possible
to collate all recent offshore survey datasets,
particularly those from commercial surveys
that are not in the public domain.
For most species in this report, the geo-
graphical scope covers all British waters (up
to 200 nautical miles, or 370.4 km), or to the
international boundary, if closer. However, it
should be noted that estimates are derived
mostly from data collected in the terrestrial
and near-inshore parts of Great Britain (and
even inshore waterbird survey datasets are
very limited) together with limited ad-hoc
offshore surveys or modelled estimates for
some species that have significant offshore
wintering populations. For some species –
Great Cormorant Phalacrocorax carbo, Black-
throated Diver Gavia arctica and gulls – the
lack of information has meant that estimates
relate to terrestrial and near-inshore (up to
one nautical mile) populations only and no
attempt has been made to estimate offshore
numbers. The estimate for Great Northern
Diver G. immer is based on coastal data from
NEWS III only, but is similar to a recent mod-
elled estimate including some offshore areas.
All species which have significant distribu-
tions beyond one nautical mile are marked as
‘M’ under ‘Reliability’ in table 1; see notes in
table 1 for how far offshore evidence has
been taken into account. Note that, even
where offshore data have been used, esti-
mates should generally be taken to be
minimum estimates at the whole GB level,
and should not be taken, for regulatory pur-
poses, as pertaining to the whole of the
national territory out to 200 nautical miles,
since our knowledge is limited about the
numbers of birds using such areas.
Winter estimates are derived for the
132
Frost et al.
British Birds 112 • March 2019 • 130 –145
86. Male Common Pochard Aythya ferina, Northumberland, January 2006. The wintering Pochard
population in Britain has been decreasing (the current estimate is 23,000 birds) and breeding
numbers have been declining across Europe also. Possible causes that have been suggested include
changes in wetland management and water quality, water abstraction and drought in southeast
Europe, and non-native predators.
David Tipling
period September to March for most species,
and any deviations are noted in table 1. For
species whose estimates are based on WeBS
and/or NEWS, January-only estimates are
also given. In January, waterbird monitoring
coverage extends throughout the African-
Eurasian Flyway for the International
Waterbird Census (IWC), a standardised and
synchronised survey carried out by experi-
enced volunteer birdwatchers and coordi-
nated by Wetlands International (Delany
2005). Robust country January estimates
could improve the estimates of flyway popu-
lation trends from IWC data, as they could be
incorporated as a weighting factor (Tom
Langendoen pers. comm.).
For most species, estimates are the mean
peak wintering population during the period
2012/13 to 2016/17. For scarce species, not
well covered by national monitoring schemes
and for which county bird report information
is the main data source, mean occurrence for
2011/12 to 2014/15 was generally used, as
reports for many counties were not yet avail-
able for the 2015/16 and 2016/17 winters. For
those species where the population is
changing rapidly and there is considered to be
accurate data, the estimate is based on the
most recent year or two years only, which in a
few cases includes the 2017/18 winter (noted
in table 1). Estimates from Musgrove et al.
(2011) are repeated for species where more
recent information is unavailable, less com-
prehensive and/or less reliable.
Methods
For most species, methods follow those of
Musgrove et al. (2011), using one of the
following: census data from targeted surveys
for particular species; existing published esti-
mates; extrapolation from WeBS and NEWS
data; compilation of county/regional data
from county bird reports, BirdTrack and
other sources including marine aerial
surveys; or calculations based on breeding
data. Estimates and derived 1% population
thresholds are rounded following the con-
ventions set out by Musgrove et al. (2011).
The method used for each species is listed
with the estimate in table 1.
To calculate the estimate for species based
solely on WeBS data, we first used the stan-
dard WeBS indexing method to generate any
missing or incomplete counts at all sites
where the species has occurred (Underhill &
Pryˆs-Jones 1994; BTO 2017). Counts were
summed across sites for each month between
September and March inclusive and the
maximum monthly total established for each
year. The mean of these annual maxima over
the five-year period was used for the main
winter estimate (and the January figure used
for the January-only estimate). For species
which are highly detectable and which are
133British Birds 112 • March 2019 • 130 –145
Population estimates of wintering waterbirds
Richard Chandler
87. Eurasian Teals Anas crecca, Northamptonshire, February 2010. This is one of the more difficult
species to survey, since Teals occur widely throughout the countryside. A new method that models
data from WeBS, Bird Atlas 2007–11 and environmental metrics has resulted in an estimate of
430,000 birds, a large increase on previously published estimates.
thought to occur only rarely on non-WeBS
sites, this forms the population estimate. For
species that occur more widely inland or have
low detectability, the figure is scaled upwards
by an extrapolation factor derived from
intensive local studies (Musgrove et al. 2011).
Extrapolation factors used are specified in
the species notes to table 1.
For some species that are widely dispersed
across Great Britain, we considered it more
accurate to use an environmental stratifica-
tion method, as developed by Méndez et al.
(2015) for estimating waterbird populations,
instead of the extrapolation factor approach.
The extrapolation approach relies on local
studies, which may not reflect differences in
habitat availability across the country,
whereas Méndez et al. used a wider range of
information about the distribution of wetland
habitats and waterbirds. For this environ-
mental stratification method, the country was
divided into 5×5 km squares that were
assigned to 64 environmental strata deter-
mined by freshwater extent and complexity,
altitude and urban extent. National estimates
were produced by modelling bird abundance
in each stratum based on WeBS counts and
distribution data from Bird Atlas 2007–11
(Balmer et al. 2013); for more details see Frost
et al. (2016) and Méndez et al. (2015). Of the
19 widely dispersed species investigated,
Méndez et al. recommended this approach for
estimates of Mute Swan Cygnus olor, Canada
Goose Branta canadensis, Eurasian Teal Anas
crecca, Tufted Duck Aythya fuligula, Great
Crested Grebe Podiceps cristatus and
Common Coot Fulica atra. Here, this method
was used for these species based on updated
We BS d a t a f r o m 2 01 2 / 1 3 t o 2 0 1 6/ 1 7 . F o r t h e
other widespread species considered, further
refinements to the method, or improved data,
are needed to generate robust estimates
(Méndez et al. 2015).
Méndez et al. (2015) attempted to esti-
mate Egyptian Goose Alopochen aegyptiaca
numbers using the environmental stratifica-
tion approach, but the result was considered
an underestimate caused by under-represen-
tation of relevant habitats in WeBS sites.
Here, a new extrapolation figure was derived
by comparing the Norfolk estimate in Taylor
& Marchant (2011) with WeBS data for the
same area and time period. Extrapolation
figures for all other species are unchanged
from those in Musgrove et al. (2011) and
given in the notes to table 1.
134
Frost et al.
British Birds 112 • March 2019 • 130 –145
88. Great Northern Diver Gavia immer, Pembrokeshire, January 2013. Surveyors were asked to
count waterbirds at sea during the 2015/16 Non-estuarine Waterbird Survey (NEWS) III and this
was the first NEWS survey where estimates were produced for all waterbirds, rather than just
waders. The total of 4,300 Great Northern Divers is based solely on the NEWS III estimate and
so may be an underestimate, but is similar to the 4,000 given in Furness (2015).
Richard Stonier
Musgrove et al. (2011) presented an
estimate for the Little Egret Egretta garzetta
based solely on WeBS counts with no extrapo-
lation to other wetlands. The environmental
stratification method is not ideal for such
rapidly increasing species colonising new
regions and habitats, but it was used here for
Little Egret since no intensive surveys are avail-
able to provide an extrapolation factor. Since
WeBS coverage is considered incomplete for
this species, we consider the stratified habitat
estimate to be the best currently available.
WeBS sites are classified as inland, estu-
arine or non-estuarine, but coverage of the
non-estuarine coast is relatively low by this
survey. For species considered to have signifi-
cant populations on non-estuarine coasts, we
excluded non-estuarine WeBS sites and
incorporated the non-estuarine population
estimates from Austin et al. (2017), based on
the 2015/16 NEWS III survey, which covered
landward, seaward and intertidal habitats of
the non-estuarine coast. Austin et al. used a
bootstrap method over coastal stretches to
produce January 2016 non-estuarine esti-
mates for relevant species from the NEWS III
data (note that while the estimate is for
January 2016, some stretches of coast were
surveyed in December 2015 or February
2016). Estimates were produced for all water-
birds that were sufficiently recorded by the
survey, whereas previous NEWS surveys had
produced estimates for waders only. The
January 2016 non-estuarine estimate was
scaled for the other months and years and
added to the estimate from WeBS data for
estuarine and inland sites (scaled by an
extrapolation factor where appropriate) to
produce the total winter and January esti-
mates. Species for which NEWS III estimates
were incorporated are indicated in table 1.
The Mandarin Duck Aix galericulata esti-
mate in Musgrove et al. (2011) repeated an
estimate based on data up to 1987 (Davies
1988). A new method was used this time.
Within the London Bird Atlas area
(Woodward et al. 2017), a density estimate of
40 individuals per occupied 10-km square
was derived from all survey data for Bird
Atlas 2007–11. Elsewhere, a density estimate
of 21 individuals per occupied 10-km square
was derived from Timed Tetrad Visits for
Bird Atlas 2007–11; this was adjusted for
lower detection rates outside London by a
factor derived by comparing the number of
Mandarin Ducks recorded per hour during
Timed Tetrad Visits within and outside the
London Atlas area. These two density esti-
mates (within/outside London) were used to
calculate the revised population estimate.
For 24 species, monthly totals were manu-
ally extracted from up to six years (2011–16)
of bird reports for 89 counties/regions to
generate the bird-report dataset used in this
assessment. For relevant species these data
were combined with data from WeBS, NEWS
and 10-km square maxima counts from
BirdTrack (BTO/RSPB/BirdWatch Ireland/
SOC/WOS 2018) on a regional basis to
produce an estimate. Further source details
are given in the species notes in table 1.
Results
Estimates for peak winter populations are
given in table 1. The type of method used to
produce the estimate is shown, and a guide to
the reliability of the estimate, together with
an indicator (‘M’) for marine species, where
the estimate should be considered a
minimum. An indication is given of the cause
of any change in the estimate since Musgrove
et al. (2011), such as whether this is due to
improved methods or data, or is considered to
be a genuine change. If there is a genuine
change, the direction (increase/decrease)
is indicated by a +/- symbol. The GB 1%
threshold of the winter estimate is given for
native species; this figure is important because
it is used for identifying and designating sites
of importance for bird populations. Note that
when the 1% threshold is below 50 birds, 50 is
normally used as the minimum qualifying
threshold for the designation of sites of
importance (Stroud et al. 2001).
Table 1 includes six species not covered by
Musgrove et al. (2011), although winter esti-
mates for White-billed Diver G. adamsii,
Great White Egret Ardea alba and Common
Crane Grus grus were published in Musgrove
et al. (2013). The estimate is unchanged for
14 species or populations: for 12 of these the
previous estimate has been repeated, while
for Svalbard Light-bellied Brent Goose
Branta bernicla hrota and British Greylag
135British Birds 112 • March 2019 • 130 –145
Population estimates of wintering waterbirds
continued on page 140
136
Frost et al.
British Birds 112 • March 2019 • 130 –145
Table 1. Population estimates of wintering waterbirds in Great Britain, 2012/13 to 2016/17.
KEY: Method: W WeBS + extrapolation, 2012/13 to 2016/17; WN WeBS + extrapolation + NEWS, 2012/13
to 2016/17; C species-specific census data, dates as in notes; S WeBS + environmental stratification
approach, 2012/13 to 2016/17; O compilation of county/regional/other sources data, 2011/12 to 2014/15
unless otherwise noted; M miscellaneous, dates as in notes/sources; R estimate repeated from Musgrove et
al. (2011).
Reliability: 1 good-quality counts of most of the individual birds; 2 based mostly on count data but with a
large degree of extrapolation; 3 not strongly based on actual count data and/or where large assumptions
have been made and/or estimates suspected/known to be based on incomplete data; M species with
significant distributions beyond one nautical mile. Owing to limited offshore data, estimates may simply
refer to the terrestrial and near-shore environment. Where estimates include offshore data, they may still
be underestimates in relation to the whole of the national territory. See individual species notes for details.
Change (from Musgrove et al. 2011) a+ yes, increased due to genuine change; a- yes, decreased due to
genuine change; b yes, due to improved knowledge or more accurate data; c yes, due to the use of a
different method; d yes, but there is no information on the nature of the change; — species was not
included in Musgrove et al. 2011; N no change (see Method column for whether this is repeated (R), or a
new estimate that is the same as the old one.
Species Scientific name Estimate 1% Method Reliability Change Note
threshold
Brent Goose Branta bernicla bernicla 98,000 980 W 1 a+
(Dark-bellied)
Brent Goose Branta bernicla hrota 3,400 34 W 1 N
(Svalbard Light-bellied)
Brent Goose Branta bernicla hrota 1,600 16 W 1 a+
(Nearctic Light-bellied)
Canada Goose Branta canadensis 160,000 n/a S 2 c 1
Barnacle Goose Branta leucopsis 4,400 n/a O 2 a+
(Naturalised)
Barnacle Goose Branta leucopsis 56,000 560 C 1 a- 2
(Greenland)
Barnacle Goose Branta leucopsis 43,000 430 C 1 a+ 3
(Svalbard)
Snow Goose Anser caerulescens 75 n/a O 2 a- 4
Greylag Goose Anser anser 140,000 1,400 W 2 N 5
(British)
Greylag Goose Anser anser 91,000 910 C 2 a+ 6
(Icelandic)
Taiga Bean Goose Anser fabalis 230 2 C 1 a- 7
Pink-footed Goose Anser brachyrhynchus 510,000 5,100 C 1 a+ 8
Tundra Bean Goose Anser serrirostris 300 3 O 1 a- 9
White-fronted Goose Anser albifrons albifrons 2,100 21 W 1 a-
(European)
Notes: 1. The decrease compared with Musgrove et al. (2011) is due to the change to using the environmental
stratification method. The ten-year (2005/06 to 2015/16) population trend for Canada Goose is +12% (Frost et al. 2018).
2. The estimate is the rounded Scottish count for spring 2018 (Mitchell & Hall in prep.).
3. The estimate is the rounded mean of the two highest counts during the 2017/18 winter, including birds on the Solway
Estuary and from the Svalbard population that wintered on the east coast earlier in the winter (WWT 2018).
4. The population on Coll has declined to 10–20 birds (J. Bowler pers. comm.).
5. An extrapolation factor of 1.96 has been used.
6. The estimate is the mean of 2012/13 to 2016/17 international censuses and includes adjustments to remove resident
birds and those in Norway and Ireland (Mitchell & Brides 2017).
7. The estimate is the rounded average peak British count for the 2016/17 and 2017/18 winters.
8. The estimate is the rounded average peak British count for October 2015 and 2016; earlier data are not used due to
rapid population change (Mitchell 2016; Mitchell & Brides 2017).
9. Five-year mean of BirdTrack data only for 2012/13 to 2016/17. Estimates vary greatly from year to year, from less than
100 in some years to over 800 in 2016/17.
137British Birds 112 • March 2019 • 130 –145
Population estimates of wintering waterbirds
Species Scientific name Estimate 1% Method Reliability Change Note
threshold
White-fronted Goose Anser albifrons flavirostris 12,000 120 C 1 a- 10
(Greenland)
Mute Swan Cygnus olor 50,000 500 S 2 c 11
Bewick’s Swan Cygnus columbianus 4,400 44 C 1 a- 12
Whooper Swan Cygnus cygnus 16,100 160 C 1 a+ 13
Egyptian Goose Alopochen aegyptiaca 5,600 n/a W 2 c 14
Common Shelduck Tadorna tadorna 47,000 470 WN 1 a- 15
Mandarin Duck Aix galericulata 13,000 n/a M 3 ac+ 16
Shoveler Spatula clypeata 19,000 190 W 1 a+ 17
Gadwall Mareca strepera 31,000 310 W 1 a+ 18
Eurasian Wigeon Mareca penelope 450,000 4,500 WN 1 c 19
Mallard Anas platyrhynchos 670,000 6,700 W 3 a- 20
Pintail Anas acuta 20,000 200 W 1 a-
Eurasian Teal Anas crecca 430,000 4,300 S 2 c 21
Red-crested Pochard Netta rufina 570 n/a W 1 a+
Common Pochard Aythya ferina 23,000 230 W 1 a- 22
Tufted Duck Aythya fuligula 130,000 1,300 S 1 c 23
Greater Scaup Aythya marila 3,900 39 O 2M d 24
Common Eider Somateria mollissima 77,000 770 O 2 b 25
(except Shetland)
Common Eider Somateria mollissima 4,600 46 O 1 a- 26
(Shetland)
Velvet Scoter Melanitta fusca 3,400 34 O 2M b 27
Common Scoter Melanitta nigra 130,000 1,300 O 3M b 28
Long-tailed Duck Clangula hyemalis 13,000 130 O 2M b 25
Common Goldeneye Bucephala clangula 19,000 190 WN 2 c 29
Smew Mergellus albellus 130 1 W 1 a-
Notes: 10. The estimate is the rounded peak British count for spring 2017 (Fox et al. 2017).
11. The large decrease from Musgrove et al. (2011) is due to a change in method to the environmental stratification
approach, which is considered more accurate for this species.
12. Census data from January 2015 (WWT 2017).
13. Census data from January 2015 (Hall et al. 2016).
14. Increase largely due to a change in method – a new extrapolation figure of 3.6 has been derived using Norfolk data
for 1999–2007.
15. Method change – NEWS has been used for non-estuarine component for the first time. For inland and estuary
habitats an extrapolation factor of 1.02 has been used.
16. Calculation using an estimate of 41 individuals per 10-km square derived from London Bird Atlas data (Woodward et
al. 2017) and an estimate of 21 individuals per 10-km square elsewhere based on Bird Atlas 2007–11 (Balmer et al. 2013).
17. An extrapolation factor of 1.16 has been used.
18. An extrapolation factor of 1.18 has been used.
19. The estimate would have decreased if not for a change to incorporate the non-estuarine coast estimate (Austin et al.
2017). For inland and estuary habitats an extrapolation factor of 1.05 has been used.
20. An extrapolation factor of 4.0 has been used.
21. The doubling of the estimate compared with Musgrove et al. (2011) is due to the change to the environmental
stratification method; the previous extrapolation approach is thought to underestimate the number of birds (Méndez et
al. 2015).
22. An extrapolation factor of 1.22 has been used.
23. The increase compared with Musgrove et al. (2011) is due to the change to using the environmental stratification
method; the previous extrapolation approach was thought to underestimate the number of birds (Méndez et al. 2015).
24. Combination of data from WeBS, bird reports and Lawson et al. (2015).
25. Combination of data from WeBS, bird reports and Lawson et al. (2015). Increase thought due to additional data
rather than population change.
26. Shetland-wide census of moulting Common Eiders in August 2015 (Heubeck et al. 2018).
27. Combination of data from WeBS, NEWS, bird reports and Lawson et al. (2015).
28. Combination of data from WeBS, bird reports, Lawson et al. (2015, 2016a, 2016b) and Voet (2017). Considered an
underestimate, as it is known that an unpublished regional estimate greater than this has been made from aerial survey data.
29. Method change – NEWS has been used for non-estuarine component for the first time. For inland and estuary
habitats an extrapolation factor of 1.26 has been used.
138
Frost et al.
British Birds 112 • March 2019 • 130 –145
Species Scientific name Estimate 1% Method Reliability Change Note
threshold
Goosander Mergus merganser 15,000 150 WN 2 c 30
Red-breasted Merganser Mergus serrator 10,000 100 WN 2 c 31
Ruddy Duck Oxyura jamaicensis 19 n/a M 1 a- 32
Red-throated Diver Gavia stellata 21,000 210 O 3M c 33
Black-throated Diver Gavia arctica 560 6 R 3M N 34
Great Northern Diver Gavia immer 4,300 43 O 3M ac+ 35
White-billed Diver Gavia adamsii 80 1 M 3M — 36
Little Grebe Tachybaptus ruficollis 15,000 150 W 2 a- 37
Red-necked Grebe Podiceps grisegena 59 1 O 2 d 38
Great Crested Grebe Podiceps cristatus 17,000 170 S 1 ac- 39
Slavonian Grebe Podiceps auritus 920 9 O 2 d 38
Black-necked Grebe Podiceps nigricollis 120 1 W 1 d
Glossy Ibis Plegadis falcinellus 27 1 O 1 —
Eurasian Spoonbill Platalea leucorodia 110 1 O 1 a+
Eurasian Bittern Botaurus stellaris 800 8 M 2 a+ 40
Cattle Egret Bubulcus ibis 65 1 O 2 — 41
Grey Heron Ardea cinerea 45,000 450 C 2 ab- 42
Great White Egret Ardea alba 72 1 O 2 —
Little Egret Egretta garzetta 11,000 110 S 2 ac+ 43
Shag Phalacrocorax aristotelis 110,000 1,100 R 2M N 44
Great Cormorant Phalacrocorax carbo 62,000 620 WN 2M ac+ 45
Water Rail Rallus aquaticus — n/a n/a n/a —
Moorh en Gallinula chloropus 300,000 3,000 W 3 a- 46
Common Coot Fulica atra 200,000 2,000 S 1 c 47
Common Crane Grus grus 180 2 M 1 — 48
Notes: 30. Method change – NEWS has been used for non-estuarine component for the first time. For inland and
estuary habitats an extrapolation factor of 2.95 has been used.
31. Increase due to method change – NEWS has been used for non-estuarine component for the first time.
32. Estimate 20–30 (I. Henderson; Animal & Plant Health Agency pers. comm.).
33. Estimate is that calculated in Furness (2015) except that it has been increased by the replacement of the southwest
North Sea area with the estimate published in Goodship et al. (2015) of 14,000 birds. However, recent unpublished
surveys suggest that this is likely to be an underestimate.
34. Recent available information is incomplete, so the Musgrove et al. (2011) estimate has been repeated. (380
individuals were counted during the NEWS III survey, but no extrapolated estimate is available.)
35. The estimate given is based on NEWS 2015/16 data only, and is similar to the estimate of 4,000 for UK waters
calculated in Furness (2015) but may still be an underestimate.
36. Estimate of 80 birds wintering at Dogger Bank based on extrapolation of boat-based counts (Thornton 2014).
37. An extrapolation factor of 2.12 has been used.
38. Combination of data from WeBS, NEWS, bird reports, Lawson et al. (2015) and O’Brien et al. (2014).
39. The decrease compared with Musgrove et al. (2011) is thought to be partly genuine and partly due to using the
environmental stratification method.
40. Estimate for 2017/18 winter based on 404 resident birds (following calculations from Wotton et al. 2011) and an
estimate of c. 390 migratory wintering birds (S. Wotton; RSPB pers. comm.).
41. Estimate based on the number present in 2016/17 only, as this is a rapidly increasing species now establishing a GB
population.
42. Calculated from Woodward et al. (2018). (Note that the Heronries Census estimates for 2004–08 have been revised
downwards slightly since Musgrove et al. (2011) based on updated counts for that period. The winter estimate for 2004–
08 is now 57,000.)
43. Increase compared with Musgrove et al. (2011) due to combination of population increase and the change to using
the environmental stratification methodology (previous estimate was not extrapolated).
44. Estimate from Musgrove et al. (2011) based on calculation from breeding estimate – not updated. The Furness
(2015) estimate of 106,000 is similar.
45. Method change – NEWS has been used for non-estuarine component for the first time. For inland and estuary
habitats an extrapolation factor of 1.6 has been used.
46. An extrapolation factor of 16.78 has been used.
47. The increase compared with Musgrove et al. (2011) is due to the change to the environmental stratification method.
The ten-year (2005/06 to 2015/16) population trend for Eurasian Coot is -8% (Frost et al. 2018).
48. Estimate for 2017/18 winter based on 100 resident birds of wild origin plus 70+ Great Crane Project birds (UK
Crane Working Group pers. comm.).
139British Birds 112 • March 2019 • 130 –145
Population estimates of wintering waterbirds
Species Scientific name Estimate 1% Method Reliability Change Note
threshold
Oystercatcher Haematopus ostralegus 290,000 2,900 WN 1 a- 49
Avo ce t Recurvirostra avosetta 8,700 87 W 1 a+
Northern Lapwing Vanellus vanellus 620,000 6,200 R 2 N 50
Europea n Golden Plover Pluvialis apricaria 400,000 4,000 R 2 N 50
Grey Plover Pluvialis squatarola 33,000 330 WN 1 a-
Ringed Plover Charadrius hiaticula 42,000 420 WN 1 ac+ 51
Whimbrel Numenius phaeopus 38 1 W 1 d 52
Eurasian Curlew Numenius arquata 120,000 1,200 WN 1 a- 49
Bar-tailed Godwit Limosa lapponica 50,000 500 WN 1 ac+ 51
Black-tailed Godwit Limosa limosa 39,000 390 W 1 b 53
Turnstone Arenaria interpres 40,000 400 WN 1 a-
Red Knot Calidris canutus 260,000 2,600 WN 1 a-
Ruff Calidris pugnax 900 9 W 1 d
Sanderling Calidris alba 20,000 200 WN 1 a+
Dunlin Calidris alpina 340,000 3,400 WN 1 a-
Purple Sandpiper Calidris maritima 9,700 97 WN 2 a-
Little Stint Calidris minuta 8 1 W 1 d 52
Woodc oc k Scolopax rusticola 1,400,000 14,000 R 3 N 54
Jack Snipe Lymnocryptes minimus 100,000 1,000 R 3 N 54
Common Snipe Gallinago gallinago 1,000,000 10,000 R 3 N 54
Common Sandpiper Actitis hypoleucos 52 1 W 1 b 52
Green Sandpiper Tringa ochropus 290 3 O 3 c 55
Common Redshank Tringa totanus 94,000 940 WN 1 a-
Spotted Redshank Tringa erythropus 67 1 W 1 a- 52
Greenshank Tringa nebularia 810 8 WN 1 a+ 52
Kittiwake Rissa tridactyla — n/a n/a n/a —
Black-headed Gull Chroicocephalus ridibundus 2,200,000 22,000 R 2M N 56
Little Gull Hydrocoloeus minutus — n/a n/a n/a —
Mediterranean Gull Ichthyaetus melanocephalus 4,000 40 O 2 a+
Common Gull Larus canus 700,000 7,000 R 2M N 54
Great Black-backed Gull Larus marinus 76,000 760 R 2M N 54
Glaucous Gull Larus hyperboreus 160 2 O 2M d 57
Iceland Gull Larus glaucoides 330 3 O 2M d 58
Herring Gull Larus argentatus 730,000 7,300 R 2M N 54
Caspian Gull Larus cachinnans 130 1 O 2 d
Yellow-legged Gull Larus michahellis 840 8 O 2 d
Lesser Black-backed Gull Larus fuscus 120,000 1,200 R 2M N 54
Sandwich Tern Thalasseus sandvicensis 53 1 O 1 —
Notes: 49. Note that the decrease compared with Musgrove et al. (2011) would have been more pronounced if not for
methodology change in estimating the non-estuarine population (Austin et al. 2017).
50. Estimate from Musgrove et al. (2011) and Gillings & Fuller (2009) – not updated.
51. The increase compared with Musgrove et al. (2011) is partly due to the method change for estimating the non-
estuarine population (Austin et al. 2017).
52. November–March only, to exclude migrants present in September and October.
53. Decrease compared with Musgrove et al. (2011) is due to improved data on some major estuaries which only had
incomplete counts in the last assessment, leading to overestimation of numbers; note population trend is increasing for
this species (Frost et al. 2018).
54. Estimate from Musgrove et al. (2011) – not updated.
55. The estimate is lower than the previous one, partly due to a restriction to core wintering months of November–
March, to exclude all passage birds (October included previously). The WeBS trend suggests a reduction since the last
estimate period. This figure should be seen as a minimum as birds are likely to be overlooked.
56. Estimate from Musgrove et al. (2011) – not updated. Note that although the 1% threshold for this species is 22,000,
in reality a site that regularly supports in excess of 20,000 waterbirds is considered as internationally important by virtue
of absolute numbers alone.
57. Numbers vary greatly from year to year; estimate is mean over bird-report period.
58. Numbers vary greatly from year to year; estimate is mean over bird-report period and includes the 2011/12 influx
(Fray et al. 2012).
Goose Anser anser populations the estimate
was recalculated but is identical. For 41
species the same method was used and the
difference in the estimate is driven by popu-
lation change. For six species or populations
the difference is mostly due to improved
knowledge or data; for 12 species it relates to
improved methodology; for eight species it
reflects a mixture of genuine population
change and factors relating to methodology
or data availability; and for 11 species the
main driver of the difference is unclear.
Estimates for January only are presented
in table 2 for species where the methods used
have been based on WeBS and NEWS data
with either the extrapolation or environ-
mental stratification approach. The method
and reliability for these estimates are as in
table 1.
Discussion
The estimated total number of wintering
waterbirds in Great Britain is 12.8 million,
including 4.9 million waders, 3.8 million
gulls, 2.1 million ducks, 1.1 million geese,
500,000 rails, 170,000 cormorants, 70,000
swans, 60,000 herons, 30,000 divers and
30,000 grebes.
For those species where the majority of
the change in population estimate can be
attributed to genuine change in population
size rather than methodology, there has been
a gain of approximately 175,000 geese and a
loss of 142,000 overwintering waders since
the 2011 assessment. The increased goose
total is driven largely by Pink-footed Goose
Anser brachyrhy nchus and, to a lesser extent,
Dark-bellied Brent Goose Branta b. bernicla
and all three Barnacle Goose Branta leucopsis
populations (Greenland, Svalbard and
Naturalised). The key species involved in the
decrease in wader totals were Red Knot
Calidris canutus (down by 60,000 to
260,000), Oystercatcher Haematopus
ostralegus (down by 30,000 to 290,000),
Common Redshank Tr i ng a t ot a nu s (down by
26,000 to 94,000) and Eurasian Curlew
Numenius arquata (down by 20,000 to
120,000).
In absolute terms, the largest change to a
140
Frost et al.
British Birds 112 • March 2019 • 130 –145
Table 2. January population estimates of wintering waterbirds in Great Britain, 2012/13 to
2016/17. See table 1 for scientific name, method, reliability and species-specific notes.
Species Estimate Species Estimate
Brent Goose (Dark-bellied) 96,000 Black-necked Grebe 99
Brent Goose (Svalbard Light-bellied) 1,500 Little Egret 3,400
Brent Goose (Nearctic Light-bellied) 1,400 Great Cormorant 45,000
Canada Goose 140,000 Moor hen 260,000
Greylag Goose (British) 96,000 Common Coot 170,000
White-fronted Goose (European) 2,100 Oystercatcher 260,000
Mute Swan 45,000 Avoce t 7,800
Egyptian Goose 3,500 Grey Plover 29,000
Common Shelduck 47,000 Ringed Plover 19,000
Shoveler 19,000 Whimbrel 17
Gadwall 30,000 Eurasian Curlew 100,000
Eurasian Wigeon 440,000 Bar-tailed Godwit 42,000
Mallard 620,000 Black-tailed Godwit 30,000
Pintail 19,000 Turnstone 36,000
Eurasian Teal 420,000 Red Knot 210,000
Red-crested Pochard 480 Ruff 390
Common Pochard 22,000 Sanderling 18,000
Tufted Duck 130,000 Dunlin 320,000
Common Goldeneye 18,000 Purple Sandpiper 8,900
Smew 89 Little Stint 6
Goosander 14,000 Common Sandpiper 43
Red-breasted Merganser 9,500 Common Redshank 77,000
Little Grebe 11,000 Spotted Redshank 49
Great Crested Grebe 12,000 Greenshank 640
population estimate is for the Eurasian Teal;
this has increased by 220,000 to 430,000,
owing to the adoption of the environmental
stratification approach. This is a species
whose diverse habitat preferences make it
challenging to estimate accurately. The new
1% threshold is 4,300, which would mean,
for example, that five WeBS sites held nation-
ally but not internationally important
Eurasian Teal populations in 2016/17, com-
pared with 24 using the 2011 1% threshold
figure.
The largest genuine population increase is
that for Pink-footed Goose, up by 150,000 to
510,000. Other species where the estimate has
increased by over 20,000 are Common Scoter
Melanitta nigra, Common Eider Somateria
mollissima (outside Shetland, where numbers
have fallen) and Great Cormorant. The
Common Scoter estimate increased by 30,000
to 130,000, but this is still likely to be an
underestimate due to the difficulties of esti-
mating populations at sea (see below). The
Great Cormorant estimate has increased by
27,000 to 62,000, mostly due to the improved
NEWS estimate of birds using the non-estu-
arine coast. The increase in Common Eider
(outside Shetland), by 22,000 birds to 77,000,
is due to the more complete assessment by
Lawson et al. (2015). Besides Canada Goose
and the wader species mentioned above, the
only other species/population for which the
estimate has decreased by over 20,000 was
Mute Swan; the decrease in this estimate is
largely due to adoption of the environmental
stratification methodology, since the extrapo-
lation factor used previously was high.
There is a mixed story for non-native
waterbirds. The largest changes are at least
partially related to methodology (Canada
Goose, Mandarin Duck and Egyptian
Goose). Of the non-native populations where
the same methodology was employed, Snow
Goose Anser caerulescens and Ruddy Duck
Oxyura jamaicensis decreased, whereas Red-
crested Pochard Netta rufina increased.
One group where change is particularly
noticeable is the herons, although some of
the apparent increase since Musgrove et al.
(2011) is explained by methodology. The
141British Birds 112 • March 2019 • 130 –145
Population estimates of wintering waterbirds
89. Little Egret Egretta garzetta and Common Sea-lavender Limonium vulgare, Norfolk, 2012. Little
Egrets have continued to expand their range. As this is a species that can be found in the wider
countryside, the new estimate has used environmental stratification to extrapolate WeBS counts.
The winter estimate of 11,000 is higher than the January estimate of 3,400 owing to high numbers
of birds present in the autumn; in fact, September is the peak month.
Richard Chandler
Little Egret increase from 4,500 to 11,000 was
due mostly to the adoption of the environ-
mental stratification approach; using the
same methods as in 2011, the current esti-
mate would have increased only to 6,500. The
Cattle Egret Bubulcus ibis, a recent coloniser,
was absent from Musgrove et al. (2011) but
has increased rapidly in recent years; the esti-
mate of 65 individuals was based on 2016/17
data only. The estimate for Eurasian Bittern
Botaurus stellaris also increased, by 200 to
800, but the Grey Heron Ardea cinerea esti-
mate, which is based on the Heronries
Census, decreased by 16,000 to 45,000.
In general, the revised non-estuarine esti-
mation method used for the 2015/16 NEWS
III produced higher estimates than the
method used in the previous NEWS II survey.
This resulted in an increased non-estuarine
component for some species estimates, despite
non-estuarine population decreases apparent
when the revised methodology was used to
reanalyse previous survey data (Austin et al.
2017). Species particularly affected include
Oystercatcher and Eurasian Curlew.
For most species, the January estimates in
table 2 are lower than the overwinter esti-
mates in table 1 because the peak winter pop-
ulation occurs in other months. This may
reflect migration to other parts of the flyway
in midwinter and/or winter mortality. In
some cases the difference is substantial,
including estimates that are more than
halved for Svalbard Light-bellied Brent
Goose, Little Egret, Ringed Plover Charadrius
hiaticula, Whimbrel Numenius phaeopus and
Ruff Calidris pugnax.
Modern technology deployed during
aerial surveys continues to improve our
knowledge of the number of waterbirds
using our marine environment, but reports
synthesising information from disparate
sources are limited (e.g. Furness 2015,
Lawson et al. 2015). There is increasing
industrial activity in the UK’s offshore
waters, principally by the renewable energy
sector, and this is resulting in greater regula-
tory activity (such as Environmental Impact
Assessments and, for Special Protection
Areas, Appropriate Assessments), which in
turn is stimulating more marine bird surveys.
Yet these aerial and boat-based surveys are
largely undertaken for commercial interests
with a site-specific focus and there is no
national process to collate the resulting data.
This results in an unfortunate situation
where although we now know that there are
significant numbers of some non-breeding
142
Frost et al.
British Birds 112 • March 2019 • 130 –145
90. Common Shelducks Tadorna tadorna, Norfolk, March 2015. As for many estuarine waders,
the WeBS trend for Shelduck has shown a long-term decline. The current estimate of 47,000 is
correspondingly lower than that of 61,000 published in 2011.
Richard Chandler
waterbirds offshore, and indeed know that
survey data exist for some locations, we are
unable to incorporate those data here. We
highlight this as a significant need for the
future and recommend that a national
process be established, with offshore stake-
holders, to collate such data for the next
assessment (due in 2023) and other conserva-
tion activities. Where this information does
become available, it will most likely increase
the estimates: for example, our Common
Scoter estimate of 130,000 is still considered
an underestimate for British waters, as is the
Red-throated Diver Gavia stellata estimate of
21,000. The latter is based on that calculated
by Furness (2015) and increased by the
replacement of the southwest North Sea area
estimate with that of 14,000 birds published
by Goodship et al. (2015).
Ideally, a clear and sustained mechanism
for ensuring that commercially driven data
are made available promptly is needed, such
as by publishing short notes or reports. A
detailed review of marine waterbird studies
with population estimates is required to
more fully understand the number and dis-
tribution of waterbirds using the British
marine environment, perhaps utilising
species distribution modelling initiatives that
are currently being developed, such as the
marine ‘top predators’ mapping project
(MERP 2018). Ideally, this would facilitate
assessment of the offshore component of all
marine waterbirds, including gulls.
The recommendations by Musgrove et al.
(2011) to further improve wintering water-
bird population estimates still stand. The
highest priority remains to maintain and
enhance the main UK waterbird monitoring
surveys of WeBS, GSMP and NEWS. The lack
of funding for a Winter Gull Roost Survey
(WinGS) since the 2003/04–2005/06 survey
has meant that it has not been possible to
update estimates for the widespread gull
species, including the Birds of Conservation
Concern red-listed Herring Gull Larus argen-
tatus and the several amber-listed species
(Eaton et al. 2015); repeating this survey is a
priority. Estimates of Northern Lapwing
Vanellus vanellus and European Golden
Plover Pluvialis apricaria are also not
updated, as the last comprehensive Winter
Plovers survey was in 2006/07 (Gillings &
Fuller 2009). UK participation in interna-
tionally coordinated surveys of seaducks and
other marine waterbirds is also very impor-
tant, so that meaningful population size and
trend estimates can be made – this is vital
context for the assessment of the status of
British populations.
Other recommendations by Musgrove et
al. (2011) included the need for new methods
to estimate birds in the wider countryside.
Progress has been made on this with the
143British Birds 112 • March 2019 • 130 –145
Population estimates of wintering waterbirds
91. Common Scoters Melanitta nigra, Norfolk, January 2019. Monitoring populations of waterbirds
that use marine habitats, such as Common Scoter, is challenging. New technologies and requirements
around offshore developments have added to our knowledge for some areas. However, more work
is required to collate data and to understand and account for spatial biases. The current estimate of
130,000 Common Scoters is considered to be an underestimate of the numbers using British
waters, since it is known that a higher, unpublished, regional estimate has been made.
Richard Chandler
144
Frost et al.
British Birds 112 • March 2019 • 130 –145
development of the environmental stratifica-
tion approach. However, there are species that
are not easily estimated via direct counts or
the environmental stratification method, due
to low detectability or extensive use of envir -
onmental strata under-represented in WeBS,
including Mallard Anas platyrhynchos, Little
Grebe Tachybaptus ruficollis, Water Rail Rallus
aquaticus, Moorhen Gallinula chloropus,
Woo dc oc k Scolopax rusticola, Jack Snipe
Lymnocryptes minimus, Common Snipe
Gallinago gallinago and Green Sandpiper
Tr in ga o ch ro pu s . These species require further
development of methods and/or more data
from poorly represented environmental
strata, i.e. more WeBS counts from smaller
wetlands, rivers and upland regions. Detailed
local and in-depth species studies are still
required for improving extrapolation factors
for lesser-understood species such as
Mandarin Duck and Egyptian Goose. Further
work is also still required to improve under-
standing of turnover during migration and
the relative numbers and distributions of
some biogeographic populations.
Acknowledgments
Our grateful thanks go to every one of the thousands
of counters and birdwatchers who have contributed to
the main waterbird monitoring schemes (including
WeBS, NEWS III, GSMP, WinGS, the Heronries Census
and Bird Atlas 2007–11) and recording of scarcer
species through county bird recorders and BirdTrack.
We relied heavily on the work done by the national and
local organisers of those schemes and those who
collate and produce county bird reports, and extend
our thanks to all involved. WeBS is a partnership jointly
funded by the BTO, RSPB and JNCC, in association with
WWT. NEWS III was funded by SNH, NE, NRW,
DAERA, WeBS and I-WeBS. GSMP is a partnership
funded by WWT, JNCC and SNH. Additional help,
advice and information were given by Dawn Balmer,
John Bowler, Niall Bur ton, Neil Calbrade, Tim Dunn,
Colette Hall, Iain Henderson, Mark Lewis, Will Miles,
Heidi Mellan, Veronica Méndez, Andy Musgrove, David
Noble, Matt Parsons, Kirsi Peck and Andy Webb.
References
Austin, G., Frost, T., Mellan, H., & Balmer, D. 2017.
Results of the Third Non-Estuarine Waterbird Sur vey,
including Population Estimates for Key Waterbird
Species. BTO Research Repor t 697, Thetford.
Balmer, D. E., Gillings, S., Caffrey, B. J., Swann, R. L.,
Downie, I. S., & Fuller, R. J. 2013. Bird Atlas 2007–11:
the breeding and wintering birds of Britain and Ireland.
BTO, Thetford.
British Ornithologists’ Union (BOU). 2017. The British
List: a checklist of birds of Britain (9th edition).
Ibis 160: 190–240.
British Trust for Ornithology (BTO). 2017. Wetland Bird
Survey: survey methods, analysis and interpretation.
Version 2.0. BTO, Thetford.
BTO/RSPB/BirdWatch Ireland/SOC/WOS. 2018.
BirdTrack. Available at www.birdtrack.net
(Accessed July 2018.)
Burke, B., Lewis, L., Frost, T., Austin, G., & Tierney, T. D.
In press. Estimates of waterbird numbers wintering
in Ireland, 2011/12–2015/16. Irish Birds.
Davies, A. K. 1988. The distribution and status of
Mandarin Duck Aix galericulata in Britain.
Bird Study 35: 203–208.
Delany, S. 2005. Guidelines for Participants in the
International Waterbird Census (IWC). Wetlands
International, Wageningen.
Eaton, M. A., et al. 2015. Birds of Conservation
Concern 4: the population status of birds in the UK,
Channel Islands and Isle of Man. Brit. Birds 108: 708–
746.
Fox, A. D., Francis, I., Norriss, D., & Walsh, A. 2017.
Report of the 2016/2017 International Census of
Greenland White-fronted Geese. Greenland White-
fronted Goose Study/National Parks and Wildlife
Service, Co. Wexford.
Fray, R., et al. 2012. An unprecedented influx of Iceland
Gulls in the nor theastern Atlantic in
January/February 2012. Brit. Birds 105: 263–272.
Frost, T. M. 2016. Stratified population estimates. In:
Frost, T. M., et al., Waterbirds in the UK 2014/15:
The Wetland Bird Sur vey, pp. 26–27. BTO, RSPB and
JNCC, in association with WWT. BTO, Thetford.
— et al. 2018. Waterbirds in the UK 2016/17: The
Wetland Bird Survey. BTO, RSPB and JNCC, in
association with WWT. BTO, Thetford.
Furness, R. W. 2015. Non-breeding Season Populations of
Seabirds in UK waters: population sizes for Biologically
Defined Minimum Population Scales (BDMPS).
Natural England Commissioned Report 164.
Gillings, S., & Fuller, R. J. 2009. How many Eurasian
Golden Plovers Pluvialis apricaria and Nor thern
Lapwings Vanellus vanellus winter in Great Britain?
Results from a large-scale survey in 2006/07.
Wader Study Group Bull. 166: 21–28.
Goodship, N., et al. 2015. Surveys of Red-throated
Divers in the Outer Thames Estuary SPA.
Brit. Birds 108: 506–513.
Hall, C., Crowe, O., McElwaine, G., Einarsson, Ó.,
Calbrade, N., & Rees, E. C. 2016. Population size
and breeding success of Icelandic Whooper Swans
Cygnus cygnus: results of the 2015 international
census. Wildfowl 66: 75–97.
Heubeck, M., Mellor, M., & Miles, W. 2018. Ornithological
Monitoring Programme in Shetland 2017. SOTEAG,
Aberdeen.
Lawson, J. et al. 2015. An Assessment of Numbers of
Wintering Divers, Seaduck and Grebes in Inshore
Marine Areas of Scotland. JNCC Report No. 567,
Peterborough.
— et al. 2016a. An Assessment of the Numbers and
Distribution of Wintering Waterbirds and Seabirds in
Liverpool Bay/Bae Lerpwl Area of Search. JNCC
Report No. 576, Peterborough.
— et al. 2016b. An Assessment of the Numbers and
Distribution of Wintering Red-throated Diver, Little Gull
and Common Scoter in the Greater Wash. JNCC
Report No. 574, Peterborough.
Méndez, V., et al. 2015. Use of environmental
145British Birds 112 • March 2019 • 130 –145
Population estimates of wintering waterbirds
stratification to derive non-breeding population
estimates of dispersed waterbirds in Great Britain.
J. Nature Conserv. 28: 56–66.
Marine Ecosystems Research Programme (MERP).
2018. Top Predators. http://marine-
ecosystems.org.uk/Research_outcomes/
Top_predators (Accessed 24th October 2018.)
Mitchell, C. 2016. Status and Distr ibution of Icelandic-
breeding Geese: results of the 2015 inter national
census. Wildfowl & Wetlands Trust Report,
Slimbridge.
— & Brides, K. 2017. Status and Distribution of
Icelandic-breeding Geese: results of the 2016
international census. Wildfowl & Wetlands Trust
Report, Slimbridge.
— & Hall, C. In prep. Greenland Barnacle Geese
Branta leucopsis in Britain and Ireland: results of
the international census, spring 2018. Wildfowl &
Wetlands Trust, Slimbridge.
Musgrove, A. J., Austin, G. E., Hearn, R. D., Holt, C. A.,
Stroud, D. A., & Wotton, S. R. 2011. Overwinter
population estimates of British waterbirds.
Brit. Birds 104: 364–397.
— et al. 2013. Population estimates of birds in Great
Britain and the United Kingdom. Brit. Birds. 106:
64–100.
O’Brien, S. H., Win, I., Parsons, M., Allcock, Z., & Reid,
J. B. 2014. The Numbers and Distribution of Inshore
Waterbirds Along the South Cornwall Coast During
Winter. JNCC Report No. 498, Peterborough.
Scott, M., Webb, A., Irwin, C., & Caldow, R. In press.
Digital video aerial surveys of Red-throated Diver
in the Outer Thames Estuary SPA. Brit. Birds 112.
Stroud, D. A., et al. 2001. The UK SPA Network: its scope
and content. JNCC, Peterborough.
Taylor, M., & Marchant, J. H. 2011. The Norfolk Bird Atlas:
summer and winter distributions 1999–2007.
BTO Books, Thetford.
Thornton, P. 2014. Dogger Bank Teesside A & B
Environmental Statement – Chapter 11 Marine and
Coastal Ornithology. Forewind document number
F-OFC-CH-011, issue 4.1.
Underhill, L. G., & Pry
^s-Jones, R. 1994. Index numbers
for waterbird populations. I. Review and
methodology. J. Appl. Ecol. 31: 463–480.
Voet, H. 2017. Aerial Surveys in Carmarthen Bay SPA
get Common Scoter in Focus. Retrieved from
www.apemltd.co.uk/aerial-surveys-in-carmarthen-
bay-spa-get-common-scoter-in-focus
(Accessed 12th September 2018.)
Wetlands International. 2018. Waterbird Population
Estimates. Retrieved from wpe.wetlands.org
(Accessed 8th November 2018.)
Woodward, I. D., Arnold, R., & Smith, N. 2017.
The London Bird Atlas. London Natural History
Society and John Beaufoy Publishing, Oxford.
— et al. 2018. BirdTrends 2018: trends in numbers,
breeding success and sur vival for UK breeding birds.
Research Report 708. BTO, Thetford.
www.bto.org/birdtrends
Wotton, S., Grantham, M., Moran, N., & Gilbert, G.
2011. Eurasian Bittern distribution and abundance
in the UK during the 2009/10 winter.
Brit. Birds 104: 636–641.
Wildfowl & Wetlands Trust (WWT). 2017. Goose &
Swan Monitoring Programme: survey results 2016/17
Bewick’s Swan Cygnus columbianus bewickii.
WWT/JNCC/SNH, Slimbridge.
— 2018. Goose & Swan Monitoring Programme: sur vey
results 2017/18 Svalbard Barnacle Goose Branta
leucopsis. WWT/JNCC/SNH, Slimbridge.
Teresa M. Frost, Graham E. Austin, Stephen G. McAvoy and Ian D. Woodward,
BTO, The Nunnery, Thetford, Norfolk IP24 2PU; e-mail teresa.frost@bto.org
Richard D. Hearn, WWT, Slimbridge, Gloucestershire GL2 7BT
Anna E. Robinson and David A. Stroud, JNCC, Monkstone House, City Road, Peterborough PE1 1JY
Simon R. Wotton, RSPB Centre for Conservation Science, The Lodge, Sandy, Bedfordshire SG19 2DL
Teresa Frost is WeBS national organiser at the BTO, which involves coordination of the Core Count scheme
and reporting annually on the results. Graham Austin is Senior Research Ecologist in the Wetland & Marine
Research team at the BTO and has been involved in the analysis of WeBS data since the 1990s. Stephen
McAvoy is BirdTrack Support Officer in the Surveys team at the BTO. Ian Woodward is a Research Ecologist
in the Wetland & Marine Research team at the BTO and coordinates the Heronries Census. Richard Hearn
has worked on waterbird monitoring projects at the Wildfowl & Wetlands Trust for over 20 years, and has a
particular interest in developing and supporting more comprehensive monitoring of duck populations. Anna
Robinson has been JNCC representative on the WeBS steering committee since 2017. David Stroud is Senior
Ornithologist with JNCC and a long-term Greenland White-fronted Goose obsessive. Simon Wotton is a
Senior Conservation Scientist at the RSPB and has coordinated the national Bittern Monitoring Programme
since 2005.
Postscript
At a very late stage we became aware of the analysis of Scott et al. (in press) related to digital
video aerial surveys of Red-throated Diver in the Outer Thames Estuary SPA. They estimate that
population alone to be greater than our revised GB estimate (of 21,000). This indicates that our
assessment of the total size of the British non-breeding Red-throated Diver population is likely to
be an underestimate, and also further highlights the need to better integrate the multiple sources
of offshore waterbird data into future national waterbird population estimates.
