Information and Advisory Note Number 134 Back to menu
NATURAL HERITAGE TRENDS Species diversity: wintering bird species
WINTERING WILDFOWL
1. Introduction
1.1 Scotland supports internationally important populations of wintering ducks,
swans and geese. Many breed north of the Arctic Circle during the summer months,
but fly south in winter. Attracted to Scotland by relatively mild winter weather
and extensive wetlands, over half a million wildfowl were counted at Scottish
sites in the winter of 1997/98. Internationally important numbers were recorded
on 71 sites [Figure 1].
1.2 In 1997/98, Scotland's wintering swan and duck populations generally
represented about 1-5% of their European populations, with wigeon (8%) and
whooper swan (9%) being especially important. The six goose populations that
winter in Scotland, however, constitute a much higher proportion of their
respective international populations [Table 1].
Figure 1. Wetland Bird Survey sites at which
internationally important populations of
wildfowl were recorded in 1997/98. Symbol
sizes indicate the number of wildfowl species
present whose population exceeded 1% of the
relevant international population.
2. Trends
2.1 Count data, derived mainly from the Wetland Bird Survey (WeBS), are thought
to provide a reasonably accurate indication of trends in the populations of 18
native wildfowl species wintering in Scotland. Of these, between 1966 and 1998:
• 12 increased in abundance by at least 10%;
• three declined in abundance by at least 10%; and
• three species varied by less than 10%.
Table 1. The percentage of each goose population or race wintering in Scotland
during 1997/98
2.1.1 Swans. During the 1970s and 1980s, counts of mute swans in Scotland rose
steadily, peaked in 1990 and, by the late 1990s, were 27% higher than they had
been in the 1960s. By contrast, whooper swan numbers have shown more substantial
and more erratic changes. Although they also peaked in 1990, by 1993-97 numbers
had fallen by about two-thirds [Figure 2]. During the same period counts of
whooper swans in
England continued to rise, suggesting that at least part of the Scottish decline
may have been due to a redistribution of the wintering population. Mild winter
weather may also have caused them to disperse more widely, away from WeBS count
sites. Overall, the number of whooper swans wintering in Scotland was only about
12% higher in the late 1990s than it had been in the late 1960s.
Figure 2. Trends in Scottish wintering swan populations. All count data have
been converted to an index in which the 1997/98 total = '1'
2.1.2 Geese. The number of geese wintering in Scotland has increased
substantially since counts began in the 1960s, and particularly since the early
1980s [Figure 3]. Thus, the Svalbard population of the barnacle goose increased
by 429% between the late 1960s and mid-1990s, the Greenland white-fronted goose
increased by 357%, the pink-footed goose by 227%, the Greenland population of
barnacle goose by 119%, and the Iceland population of the greylag goose by 42%
[Figure 4]. The Scottish population of the greylag goose has also increased,
numbers on the Uists having doubled between the mid-1980s and 1996.
2.1.3 In most cases, improvements have been attributed to the introduction of
protective legislation in Britain and improved feeding conditions in Scotland or
on the breeding grounds. A decline in the Icelandic population of the greylag
goose since its peak in 1990 has been attributed to hunting in Iceland.
Figure 3. Trends in Scottish wintering goose populations. All count data have
been converted to an
index, in which the 1997/98 total = T.
2.1.4 Ducks. Several of Scotland's duck species are particularly responsive to
weather conditions, severe winter weather on the continent triggering an influx
of European birds [Figure 4]. This is particularly true of the five diving ducks
assessed, whose numbers,
collectively, have fluctuated more widely than that of other species. Seven of
the 12 species reached a peak during the early 1970s, and only two of these
(gadwall and pintail) have since recovered fully.
Figure 4. Changes in mean peak winter counts for two five year periods:
1966-70/71 to 1993-97/98. Count data were provided by the Wildfowl and Wetlands
Trust.
2.1.5 From 1966 to 1998, the teal more than doubled in population size, while
the mallard's population almost halved; part of a long-term decline throughout
the UK [Figure 5 - see page 7]. Five species (shelduck, shoveler, pochard,
tufted duck and goldeneye) peaked during the early-mid 1970s, but then declined.
In the case of the pochard, this decline was almost certainly due to a reduction
in distillery discharges into the Forth.
2.1.6 A more marked decline has occurred in the goosander population, which was
five times higher in 1982 than it was in 1997. The shoveler has shown a similar,
but less consistent decline in Scotland, peaking in 1967 and 1971. Its numbers
during the mid-1990s were about one-third lower than in the mid-1960s.
2.1.7 Two further dabbling ducks, the gadwall and pintail, peaked during the
early-
mid 1970s, were consistently low during the 1980s, and have since recovered. In
1994 over 700 gadwall were counted in Scotland, of which about one third were
found at Loch Leven (248).
2.1.8 Less reliable count data are available for wintering seaducks, two of
which are thought to have declined between 1971 and 1990. The UK scaup
population, of which 80-90% wintered in the Firth of Forth in the early 1970s,
underwent a marked decline during the following decade, coincident with a
reduction in grain discharges into the Firth. The common scoter has also
declined in its main stronghold, the Moray Firth, although with small local
increases elsewhere. Trends in the three other species have been less clear-cut:
velvet scoter and long-tailed duck numbers peaked in the early or mid-1980s,
while the eider population was thought to be increasing or stable by the end of
the 1980s.
3. Source
3.1 This profile has been developed using data collected by the Wetland Bird
Survey, a partnership scheme of the British Trust for Ornithology, the Wildfowl
and Wetlands Trust (WWT), the Royal Society for the Protection of Birds and the
Joint Nature Conservation Committee (Cranswick et al., 1999). Data from WWT goose
monitoring schemes have also been used. Additional data on goose populations on
Islay were provided by M.A. Ogilvie, and extracted from SNH files. International
population estimates were obtained from Madsen et al. (1999) and Rose and Scott
(1994). Likely causes of goose population trends are based on Pettifor et al.
(1997), Fox et al. (1989), Owen and Black (1999), and Pettifor et al. (1999a,b).
Trends in seaduck populations are based on Kirby et a/. 1993.
WINTERING WADERS
4. Introduction
4.1 Scotland's moors, peatlands and machair support internationally important
populations of breeding waders, many of which congregate in large numbers on
estuaries and seashores during the autumn and winter. Here, they are joined by
migrants from NE Canada, Greenland, Svalbard, Arctic Russia and Siberia. Most
waders are geographically widespread and highly mobile
species, capable of responding rapidly to adverse conditions, and to new feeding
or breeding opportunities. Consequently, national trends may partly reflect a
redistribution of populations, a change in productivity or survival, or improved
survey coverage. Through the Wetland Bird Survey (WeBS), reliable population
indices are currently available for 11 out of 18 wader species wintering in
Scotland in substantial numbers.
5. Trends
5.1 Populations of ten out of eleven wader species wintering in Scotland
increased substantially between 1969/70 and 1998/99 [Figure 6]. The greatest
proportional increases shown were those of the grey plover and black-tailed
godwit, whose populations increased approximately four-fold over a 25 year
period. In the case of the black-tailed godwit, this increase has been
attributed to an expansion in the breeding range of the Icelandic population,
while the rise in grey plover numbers is thought to reflect a shift in its
winter distribution, a reduction in hunting (Tubbs, 1991), and improved
conditions on its breeding grounds (Moser, 1988).
5.2 The curlew, whose Scottish winter population includes substantial numbers of
Scandinavian birds, has also shown a marked increase; of 166%. Along with the
sanderling, turnstone and ringed plover it is, however, one of several species
occurring in significant numbers along seashores, and in other habitats
infrequently covered by the WeBS scheme. Trend figures for these species are
therefore considered less reliable than for mainly estuarine species, such as
the knot or dunlin.
5.3 Most of the remaining wader species surveyed between 1969/70 and 1998/99
increased by 20-80%. They include the dunlin and redshank, both of which showed
a distinct peak in the mid-1970s, a dip during the early 1980s, and a gradual
recovery [Figure 7 - see page 8]. The dunlin's decline has been strongly linked
to the spread of Spartina anglica, an invasive intertidal cord grass which
reduces the area of open mudflat on which the bird forages (Goss-Custard and
Moser, 1988)
5.4 The only species showing a marked decline between 1969/70 and 1998/99 is the
knot, whose numbers dropped in the early 1970s, as a result of severe spring
weather on its Arctic breeding grounds.
5.5 For several species, recent trends
{spanning 10 years, from 1988/99) have
differed markedly from longer-term trends
(30 years from 1969/99), in the following
ways.
• The turnstone increased by 44% over the 30 year period, but declined by 32% in
1988/89-98/99.
• The bar-tailed godwit increased by 12% in 30 years, but declined by 11% in
1988/89-98/99.
• Conversely, the wintering knot population increased by 36% in 1988/89-98/99,
following its decline in the 1970s.
5.6 The extent to which trends shown in
Figure 7 reflect population change, a
redistribution, or improvements in survey
coverage is difficult to gauge. However,
comparisons between British and European
wader counts in the mid-1980s and early
1990s suggest that trends in British
populations at that time were likely to reflect
real increases in abundance, rather than a
wide-scale redistribution of European
populations (Davidson, 1998).
Figure 6. Percentage change in the number
of birds recorded at Wetland Bird Survey sites
during 1969/70-1998/99 (from Atkinson era/.,
2000). tData for 1972/73-98/99.
6. Sources
6.1 This profile has been developed using data collected by the Wetland Bird
Survey, a partnership scheme of the British Trust for Ornithology (BTO), the
Wildfowl and Wetlands Trust, the Royal Society for the Protection of Birds and
the Joint Nature Conservation Committee. Change estimates were extracted from
Atkinson et al. (2000),
and trend line data kindly provided by the BTO.
7. References
Atkinson, P.W., Austin, G.E., Burton, N.H.K., Musgrove, A.J., Pollitt, M. and
Rehfisch, M.M. (2000). WeBS Alerts 1998/99: Changes in numbers of wintering
waterbirds in the United Kingdom at national, county and Special Protection Area
(SPA) scales. BTO Research Report No. 239. Norfolk: British Trust for
Ornithology.
Cranswick, P., Pollitt, M., Musgrove, A. and Hughes, B. (1999). The Wetland Bird
Survey 1997-98: Wildfowl and Wader Counts. Slimbridge: BTO/WWT/RSPB/JNCC.
Davidson, N. (1998). Compiling estimates of East Atlantic flyway wader
populations in coastal Europe in the early 1990s: a summary of the 1996 WSG
wader populations workshop. Wader Study Group Bulletin 86:18-25.
Fox, A.D., Gitay, H., Owen, M., Salmon, D.G. and Ogilvie, M.A. (1989).
Population dynamics of Icelandic-nesting geese, 1960-1987. Ornis Scandinavica
20:289-297.
Goss-Custard, J.D. and Moser, M.E. (1988). Rates of change in the numbers of
dunlin Calidris alpina wintering in British estuaries in relation to the spread
of Spartina anglica. Journal of Applied Ecology, 25:95-109.
Kirby, J.S., Evans, R.J. and Fox, A.D. (1993). Wintering seaducks in Britain and
Ireland: populations, threats, conservation and research priorities. Aquatic
Conservation: Marine and Freshwater Ecosystems. Vol. 3: 105-137.
Madsen, J., Cracknell, G. and Fox A.D. (Eds.) (1999). Goose populations of the
Western Palearctic. A review of status and distribution. Wageningen, The
Netherlands: Wetlands International Publ. No. 48. Rhonde, Denmark: National
Environmental Research Institute.
Moser, M.E. (1988). Limits to the numbers of grey plovers Pluvialis squatarola
wintering on British estuaries: an analysis of long-term population trends.
Journal of Applied Ecology 25: 473-485.
Owen, M. and Black, J.M. (1999). Barnacle Goose Branta leucopsis: Svalbard. In
Madsen, J., Cracknell, G. and Fox A.D. (eds.), Goose populations of the Western
Palearctic. A review of status and distribution. Wageningen, The Netherlands:
Wetlands International Publ. No. 48. Rhbnde, Denmark: National Environmental
Research Institute.
Pettifor, R.A., Roweliffe, J.M. and Mudge, G.P. (1997). Population viability
analysis of Icelandic/Greenlandic pink-footed geese. Scottish Natural Heritage
Research, Survey and Monitoring Report No. 65. Battleby: SNH.
Pettifor, R.A., Fox, A.D. and Rowcliffe, J.M. (1999a). Greenland white-fronted
goose (Anser albifrons flavirostris) - the collation and statistical analysis of
data and Population Viability Analyses. Scottish Natural Heritage Research,
Survey and Monitoring Report No. 140. Battleby: SNH.
Pettifor, R.A., Percival, S.M. and Rowcliffe, J.M. (1999b). Greenland
populations of the barnacle goose (Branta leucopsis) - the collation and
statistical analysis of data and Population Viability Analyses. Scottish Natural
Heritage Research, Survey and Monitoring Report No. 137. Battleby: SNH.
Rose, P. and Scott, DA (1994). Waterfowl population estimates. Slimbridge, IWRB.
Tubbs, C.R. (1991). The population history of grey plovers Pluvialis squatarola
in the Solent, southern England. Wader Study Group Bull. 61:15-21.
8. Further Information
Further detailed information on Natural Heritage Trends: Species Diversity can
be found in Information & Advisory Note No. 129.
9. Contact
To obtain further information about any of the issues raised in this l&A Note,
please contact
Dr Phil Shaw or Ed Mackey
Environmental Audit Group
Chief Scientist's Unit
Scottish Natural Heritage
2 Anderson Place
EDINBURGH EH6 5NP
Tel: 0131-446 2464
Fax:0131-446 2405
E-mail: phil.shaw@snh.gov.uk
Figure 5. Trends in wintering duck populations in Scotland (dashed line: annual
peak counts; solid line: 5-year running means; all count data converted to an
index, in which the 1997/98 total = '1').
Figure 7. Trends in wintering wader populations in Scotland, (dashed line: mean
annual counts;
solid line: 'smoothed' counts).
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