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Conservation status of the world's swan populations, Cygnus sp. and Coscoroba sp.: a review of current trends and gaps in knowledge

Authors:
  • Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences

Abstract and Figures

Recent estimates of the world's swan Cygnus sp. populations indicate that there are currently between 1.5-1.6 million birds in 8 species, including the Coscoroba Swan Coscoroba coscoroba as an honorary swan. Monitoring programmes in Europe and North America indicate that most populations increased following the introduction of national and international legislation to protect the species during the early- to mid-20th century. A switch from feeding primarily on aquatic vegetation to foraging on farmland (especially high-energy arable crops) in winter during the second half of the 20th century, is also considered a contributing factor. Trumpeter Swans Cygnus buccinator famously increased from just 69 individuals known to exist in 1935 (although small numbers were missed) to c. 76,000 at the present time, and most of the northern hemisphere swan populations have continued to show increasing/stable trends over the last 20 years. The exception to this pattern is a decline since 1995 in the Northwest European Bewick’s Swan population, following an increase in its population size during the 1970s–1980s, which is now being addressed through implementation of an International Single Species Action Plan. A proposal to change enforcement regulations of the Migratory Bird Treaty Act in the United States is also of concern, as potentially undermining protection for Trumpeter Swans in North America, illustrating the importance of politics and legislation as well as on-the-ground measures for species conservation. Elsewhere, less is known about the trends and conservation status for swans in central and eastern Asia, though count and research programmes introduced in China, added to those underway in Japan and Korea, have recently greatly enhanced our knowledge of swan populations on the East Asian flyway. Trends for the Black Swan Cygnus atratus in Australia and for the Black-necked Swan Cygnus melancoryphus in South America are also poorly known, because of the large numbers involved for the former and a lack of coordinated counts across difficult terrain for the latter. These southern hemisphere species are considered vulnerable to water resource developments (i.e. where diversion of water is shrinking wetlands), and to droughts associated with El Nino events and climate change. More extensive monitoring is therefore required to determine whether swan populations and species are stable, fluctuating or in decline.
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©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
Conservation status of the world’s swan populations,
Cygnus sp. and Coscoroba sp.: a review of current
trends and gaps in knowledge
EILEEN C. REES1,*, LEI CAO2, PREBEN CLAUSEN3,
JONATHAN T. COLEMAN4, JOHN CORNELY5, OLAFUR EINARSSON6,
CRAIG R. ELY7, RICHARD T. KINGSFORD8, MING MA9,
CARL D. MITCHELL10, SZABOLCS NAGY11, TETSUO SHIMADA12,
JEFFREY SNYDER13, DIANA V. SOLOVYEVA14, WIM TIJSEN15,
YERKO A. VILINA16, RADOSŁAW WŁODARCZYK17 & KANE BRIDES1
1Wildfowl & Wetlands Trust, Slimbridge, Gloucestershire GL2 7BT, UK.
2State Key Laboratory of Urban and Regional Ecology,
Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences,
18 Shuangqing Road, Haidian District, Beijing 10085, Peoples Republic of China.
3Department of Bioscience, Aarhus University, Kalø, Grenåvej 14, DK-8410 Rønde, Denmark.
422 Parker Street, Shailer Park, Brisbane 4128 AU, Australia.
5The Trumpeter Swan Society, 7091 Fox Circle, Larkspur, Colorado, 80118, USA.
6Smararima 39, IS-112 Reykjavik, Iceland.
7Alaska Science Center, U.S. Geological Survey, 4210 University Drive, Anchorage, Alaska 99508, USA.
8Centre for Ecosystem Science, University of New South Wales, Kensington 2052,
New South Wales, Australia.
9Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences,
No. 40 (3) Beijing Road, Urumqi 830011, Xinjiang, Peoples Republic of China.
1055 Eagle Creek Road, Wayan, Idaho 83285, USA.
11Wetlands International, P.O. Box 471, 6700 AL Wageningen, the Netherlands.
12The Miyagi Prefectural Izunuma-Uchinuma Environmental Foundation. 17-2 Shikimi,
Wakayanagi, Kurihara-city, Miyagi 989-5504, Japan.
13Western Oregon University, Department of Biology, 345 N Monmouth Ave, Monmouth Oregon, USA.
14Institute of Biological Problems of the North, Portovaya Street 18, Magadan 685000, Russia.
15Poelweg 12, 1778 KB Westerland, the Netherlands.
16School of Veterinary Medicine, University of Santo Tomas, Ejercito 146, Santiago, Chile.
17Faculty of Biology and Environmental Protection, University of Łód´z, Banacha 1/3,
90-237 Łód´z, Poland.
*Correspondence author. E-mail: Eileen.Rees@wwt.org.uk
Abstract
Recent estimates of the world’s swan Cygnus sp. populations indicate that there are
currently between 1.5–1.6 million birds in 8 species, including the Coscoroba Swan
36 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
Coscoroba coscoroba as an honorary swan. Monitoring programmes in Europe and North
America indicate that most populations increased following the introduction of
national and international legislation to protect the species during the early- to mid-20th
century. A switch from feeding primarily on aquatic vegetation to foraging on farmland
(especially high-energy arable crops) in winter during the second half of the 20th
century, is also considered a contributing factor. Trumpeter Swans Cygnus buccinator
famously increased from just 69 individuals known to exist in 1935 (although small
numbers were missed) to c. 76,000 at the present time, and most of the northern
hemisphere swan populations have continued to show increasing/stable trends over the
last 20 years. The exception to this pattern is a decline since 1995 in the Northwest
European Bewick’s Swan population, following an increase in its population size during
the 1970s–1980s, which is now being addressed through implementation of an
International Single Species Action Plan. A proposal to change enforcement regulations
of the Migratory Bird Treaty Act in the United States is also of concern, as potentially
undermining protection for Trumpeter Swans in North America, illustrating the
importance of politics and legislation as well as on-the-ground measures for species
conservation. Elsewhere, less is known about the trends and conservation status for
swans in central and eastern Asia, though count and research programmes introduced
in China, added to those underway in Japan and Korea, have recently greatly enhanced
our knowledge of swan populations on the East Asian flyway. Trends for the Black
Swan Cygnus atratus in Australia and for the Black-necked Swan Cygnus melancoryphus in
South America are also poorly known, because of the large numbers involved for the
former and a lack of coordinated counts across difficult terrain for the latter. These
southern hemisphere species are considered vulnerable to water resource developments
(i.e. where diversion of water is shrinking wetlands), and to droughts associated with El
Nino events and climate change. More extensive monitoring is therefore required to
determine whether swan populations and species are stable, fluctuating or in decline.
Key words: conservation effort, population sizes, swans, trends.
development of nature conservation during
the 20th century, long-term monitoring
of most of the world’s swan species has
been undertaken as part of waterbird count
programmes, to provide information on
population trends, assess their conservation
status, and to inform the management of
the birds and their habitats.
Information gained from national
monitoring programmes to determine
Swans have long been revered by man for
their grace and beauty, whilst also long being
exploited for food, feathers and sport. Until
the development and increased accessibility
of firearms during the 19th century, the
risk of over-harvesting was relatively low,
because the potential for mass exploitation
was limited to local moulting concentrations,
when the birds are flightless for c. 4 weeks
during the summer (Matthews 1972). With the
Conservation status of the world’s swan populations 37
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
waterbird numbers, trends in numbers
and the location of key sites has been
collated by Wetlands International for the
Waterbird Population Estimates (WPE)
programme, which serves to identify total
numbers and trends for biogeographical
populations globally (Wetlands International
2019a). These total population estimates
are used to identify sites of international
importance (defined as those holding 1%
of the population; Scott 1980), which are
priorities for protection under global
conventions (i.e. the Ramsar Convention on
Wetlands and the Convention on Migratory
Species), and are also a focus for international
conservation partnerships (e.g. the East-Asian
Australasian Flyway partnership). The data
also serve regional conservation legislation
such as the European Union’s Birds Directive
and the African-Eurasian Waterbirds
Agreement (AEWA), whose most recent
Conservation Status Report No. 7 (CSR 7)
has updated population status and trends
for all of the populations migrating within
the AEWA region. They also inform
classification of the conservation status of
species on the International Union for
Conservation of Nature (IUCN) Red List,
with all swan species currently classified as
of “Least Concern” (IUCN 2016) at the
global (rather than the population) level.
Trends in numbers and population sizes for
some swan populations are reported at regular
intervals; for instance, the surveys undertaken
of Trumpeter Swans Cygnus buccinator and
Tundra Swans (also known as Whistling
Swans) Cygnus c. columbianus by the U.S. Fish
and Wildlife Service in North America (most
recently, at the time of writing, in Groves
2017; Olsen 2018; Roberts & Paddington
2018; U.S. Fish & Wildlife Service 2019). A
review of current knowledge contributing
to assessment of the conservation status of
the world’s swan populations is warranted,
however, in order to identify gaps in
knowledge where more data are needed, and
thus identify not only populations of
conservation concern but those for which the
population size and trends are not known and
the conservation status therefore is unclear.
Here we therefore describe the most
recent published information on population
sizes and trends for swan species globally,
augmenting information provided in Wetland
International’s WPE (Wetlands International
2019a) with reports and expert opinion
from members of the IUCN-SSC/Wetlands
International Swan Specialist Group and
other researchers. The overall aims are: to
review current swan population trends; to
identify areas where further work is required
(e.g. through conservation action or filling
gaps in knowledge); to outline potential
threats to swan populations; and thus assess
where there may be cause for concern and
conservation action.
General approach
Given that Wetlands International collates
information on waterbird population trends
globally, we commenced by inspecting the
most current population size records for
the Cygnini tribe, either using Waterbird
Population Estimates No. 5 (WPE 5) or, for
the AEWA region, the Conservation Status
Report No. 7 (CSR 7), both of which can
be accessed via the online database
(http://wpe.wetlands.org/). The Cygnini
encompasses not only the Cygnus sp. but also
the Coscoroba genera with its one species –
38 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
the Coscoroba Swan Coscoroba coscoroba.
The Coscoroba Swan’s taxonomic status
continues to be a matter of debate – with
molecular analysis not supporting a close
relationship between Coscoroba and the other
swans (review in Callaghan et al. 2005) – but
as it is consistently reported in conjunction
with other swan species (e.g. Scott & the
Wildfowl Trust 1972) it is included here for
completeness. Population trend assessments
developed for the CSR 7 on migratory
waterbirds within AEWA (Wetlands
International 2019b, c) are also considered
in the species accounts. These were derived
mainly on analysis of the mid-January
International Waterbird Census (IWC) –
systematic surveys of waterbirds at specific
wetland sites – undertaken since 1967 by
national count programmes across Europe
and more widely (Delany et al. 1999).
Of the five swan species and subspecies
in the northern hemisphere, the Tundra
Swan and Trumpeter Swan of North
America, and the Bewick’s Swan C. c. bewickii
(conspecific with the Tundra Swan) and
Whooper Swan C. cygnus in Eurasia, all
migrate over long-distances between their
breeding and wintering areas (Kear 2005),
whereas the Mute Swan C. olor is relatively
sedentary in its native Eurasia and also in
North America where it has expanded after
being introduced from the 19th century
onwards (e.g. Snow & Perrins 1998; Petrie &
Francis 2003; Gayet et al. in press). Here we
consider the migratory swan populations by
region (i.e. North America vs. Eurasia), in
order to consider threats and conservation
measures in relation to the common
environmental conditions encountered on
their trans-continental flyways. The three
swan species of the southern hemisphere –
i.e. the Black-necked Swan Cygnus melancoryphus
and the Coscoroba Swan of South America
and the Black Swan Cygnus atratus of
Australia – are likewise considered in relation
to conditions occurring in these regions.
These three species are all nomadic and
move opportunistically; for instance,
Black Swans and also Black-necked Swans
disperse to ephemeral wetlands to breed
when these become available (Kingsford
et al. 1999, 2010; Vilina et al. 2002). The
conservation status of the various Mute
Swan populations globally are described in
relation to whether they are native or non-
native species in the countries concerned.
North America
Trumpeter Swans
Historically, Trumpeter Swans bred across a
wide area of North America, and the species
was also widespread in its wintering range
(Rogers & Hammer 1998; Engelhardt et al.
2000). Hunting caused numbers to drop to
near-extinction in the early 20th century – it
was thought that only 69 remained in 1935
(although it is considered that a couple of
thousand birds surviving in remote parts of
Canada and Alaska were not counted) – and
use of established migration routes waned
(Gale et al. 1987; Mitchell & Eichholz 2010).
Three main populations persist (Fig 1a): the
Pacific Coast population (PCP) which breeds
in Alaska, the Rocky Mountain population
(RMP) which breeds in the Rocky Mountains
from Yukon and Northwest Territories
south to the northern United States, and the
Interior population (IP) which includes
restored flocks in South Dakota, Minnesota,
Conservation status of the world’s swan populations 39
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
70,000
60,000
50,000
40,000
30,000
20,000
10,000
0
1968 1975 1980 1985 1990 1995 2000 2005 2010 2015
No. white swans
Year
North America total
Pacific Coast population
Rocky Mountain population
Interior population
Figure 1. Trumpeter Swans: (a) distribution and (b) population trends, both from Groves (2017). Note:
the swans’ distribution is very patchy within the broad range depicted. For detailed distribution see
Groves (2017).
(a)
(b)
40 Conservation status of the world’s swan populations
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Wisconsin Michigan and Ontario (Mitchell
& Eichholz 2010). The RMP and particularly
the IP are augmented by species
reintroduction programmes undertaken
over several decades. Legal protection from
persecution (since the 1917 Migratory Bird
Convention Act in Canada and the 1918
Migratory Bird Treaty in the USA) and
more recent conservation measures (e.g.
reintroduction programmes and creation of
reserves which protect habitats used by the
swans) have resulted in numbers recovering
during the second half of the 20th century.
Nonetheless, their distribution remains
patchy and restricted in comparison with
former times.
Systematic monitoring of the species – the
North American Trumpeter Swan Surveys
(NATSS) – commenced in 1968, with the
survey repeated in 1975 and conducted at 5-
year intervals thereafter. In 1968–2010, the
NATSS estimated Trumpeter Swan
abundance, productivity and distribution in
the northern United States and Canada,
through counts made between January–
September but primarily in April–September
(Groves 2017). Monitoring productivity
(number of cygnets) became optional in 2015
to make the surveys more cost effective;
trends in numbers therefore are now
described in terms of “white” swan (adult
and yearling) abundance. Aerial surveys of
the swans’ breeding grounds, also undertaken
in each year of the 5-year surveys, expanded
as swans were known or suspected to have
moved into adjacent habitat. Totals recorded
in the breeding range up to the year 2000
therefore represented a comprehensive
population census (of all adults and cygnets)
prior to autumn migration (Conant et al.
2002); more recently some summer surveys
have adopted a stratified sampling approach
because of the increase in area and numbers
involved (Hawkings et al. 2002). Counts made
in autumn and spring (less frequently in mid-
winter), which involved a combination of
aerial and ground surveys, were designed by
coordinators of the PCP, RMP and IP
censuses and are thus reported on a
population basis (Groves 2017).
Total population sizes recorded on the
breeding grounds increased from 2,847
birds in 1968 to 7,696 in 1980, 13,337 in
1990 and 17,155 in 2000 (Conant et al. 2002).
These were broadly similar to estimates
made in the wintering range, where numbers
increased from 2,572 white Trumpeter
Swans in 1968 to 11,344 in 1990, and 18,486
in 2000, then rose more rapidly to 25,006 in
2005 and 34,249 in 2010 (Moser 2006;
Mitchell & Eichholz 2010; Groves 2017;
Fig. 1b). That the winter counts exceeded
numbers recorded on the breeding grounds
in 2000 appears to be attributable to a
marked increase in the number of non-
migratory IP swans not included in the
arctic surveys (Fig. 1b), which in turn may be
at least partly due to reintroduction
programmes undertaken in the swans’
historic IP range (in the mid-western USA
and Ontario, Canada) since the early 1980s
(Shea et al. 2002; Handrigan et al. 2016).
The most recent pan-continental survey,
in 2015, found that total numbers have now
reached > 63,000 white birds (Table 1).
Moreover, if cygnet numbers are included
for the PCP and the RMP (where cygnets
are still counted), a total of 31,793 for
all swans in the PCP, 17,164 in the RMP
and 27,005 (white birds only) in the IP
Conservation status of the world’s swan populations 41
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
Table 1. Number of swans estimated for each species globally, derived from the Waterbird Population Estimates (WPE; Wetlands
International 2019a), and additional current estimates for each swan species. * = not including c. 50,000 Black Swans (with numbers
declining) in New Zealand in 2011 (Williams 2013), and a total of c. 13,000 Mute Swans globally in countries where they are considered
to be non-native species: North America, Japan, Australia and New Zealand. IUCN status: LC = “Least Concern” (IUCN 2016).
Species (no. of IUCN Red Current estimate Year of current Source
populations) List status estimate
Black-necked Swan (2) LC 25,000–100,000 1990–2000 Wetlands International 2019a; BirdLife 2019a
Black Swan *(1)* LC 165,000–180,000 2008 Kingsford et al. 2011; this paper
Mute Swan *(7)* LC > 650,000 2015 Wetlands International 2019a,b,c; this paper
Trumpeter Swan (3) LC 76,000 2015 Groves 2017; this paper
Whooper Swan (5) LC 249,000 2011 Laubek et al. in press; Hall et al. 2016; Jia et al.
2016; Wetlands International 2019a,b,c
Tundra Swan (2) LC 187,000 2017 Pacific Flyway Council 2001; Olson 2017;
Roberts & Padding 2017
Bewick’s Swan (3) LC 120,000 2015 Beekman et al. 2019; Wetlands International
2019a,b,c; this paper
Coscoroba Swan (1) LC 10,000–25,000 2006 Wetlands International 2019a; BirdLife 2019b
TOTAL* (24) 1.5–1.6 million
42 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
counted in 2015 indicate that total
numbers of Trumpeter Swans (including
cygnets) now exceed 76,000 (Groves 2017).
Population trends are increasing for all three
populations, but particularly for the IP
between 2010 and 2015 (Fig. 1b).
Tundra Swans
Tundra Swans – the more numerous of
the North American swan species – breed
at high latitudes in arctic Canada and
Alaska, with small numbers also breeding in
Chukotka in the Russian Arctic (Limpert
& Ernst 1994). Chukotka-breeding Tundra
Swans were estimated at 600–1,000 birds in
the early 21st century (Syroechkovski 2002),
and the proportion of these that migrate to
wintering sites in North America has yet to
be determined, though only small numbers
are recorded wintering in Japan each year
(mean ± s.d. = 35 ± 36 birds/year between
2000–2017, range = 7–160; Ministry of the
Environment 2018; T. Shimada, pers. comm.).
Counts, ringing and tracking data have
described two populations within North
America: the Eastern Population (EP) and
the Western Population (WP), which migrate
to winter along the Atlantic and Pacific
seaboards of the United States respectively
(Limpert & Ernst 1994; Ely et al. 2014; Fig. 2a).
Tundra Swans in both the EP and WP are
monitored annually by the Mid-winter
Waterfowl Surveys on the Atlantic Flyway
and the Pacific Flyway of North America.
These aerial surveys, which are a cooperative
effort between state and federal wildlife
agencies undertaken since 1955, and with
the same areas surveyed each year, aim to
obtain a complete count of waterfowl in key
wintering areas during a 1–2 week period in
early January (U.S. Fish and Wildlife Service
1989, 2019; Serie et al. 2002). The data are
considered to provide a reasonable index of
population size and long-term trends, with
productivity indices also determined from
ground counts and aerial photographs of
the proportion of grey-plumaged young
recorded in flocks at sample sites (Serie et al.
2002). For many years Tundra Swans were
protected from hunting in North America,
but in 1982 the US Fish & Wildlife Service
(USFWS) permitted the legal hunting of the
WP and in 1984, despite strong opposition,
this was expanded to the EP with
“experimental” hunting allowed in North
Carolina (Sladen 1991). Analysis of the
annual Mid-winter Waterfowl Survey data,
together with harvest survey data, therefore
is also key to the USFWS setting of annual
bag limits, which ensure that the population
meets conservation objectives for the species.
The number of WP swans recorded
during the Mid-winter Waterfowl Surveys
on the Pacific Flyway averaged at c. 55,300
birds during the second half of the 20th
century (1949–2000), and increased by 50%
in the 1970s and 1980s (Pacific Flyway
Council 2001). The population reached an
all-time high of 122,521 swans in 1997 and
nearly as many in 1999, with the most recent
estimate of 71,400 recorded in 2017 (Pacific
Flyway Council 2001; Olson 2017; Fig. 2b).
Historically, EP swans have been more
numerous than WP swans, and began to
increase significantly in the mid-1970s,
growing by 55% between the mid-1950s
and the late 1990s and peaking at c. 110,000
in 1992 until more recently 115,400 were
recorded in 2017 (Pacific Flyway Council
2001; Roberts & Padding 2017; Fig. 2b).
Conservation status of the world’s swan populations 43
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
East Population
y = 0.2971x + 89.183
R2 = 0.041
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
2016
140,000
120,000
100,000
80,000
60,000
40,000
20,000
0
No. swans
Year
West Population
y = 0.6161x + 73.114
R2 = 0.0451
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
2016
140,000
120,000
100,000
80,000
60,000
40,000
20,000
0
No. swans
Year
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
2016
No. harvested
Year
WP harvest
EP harvest
Figure 2. Tundra Swans: (a) distribution, (b) population trends (winter inventory data) and (c) harvest rates (from Pacific Flyway Council 2001; Olson
2017; Roberts & Padding 2017; Ely et al. 2014). The distribution of small numbers breeding in Chukotka, Russia, is not shown on the map.
(b)
(c)
(a)
44 Conservation status of the world’s swan populations
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Overall, the combined number of EP and
WP swans increased at an average annual rate
of about 2.1% during the period 1955–1989
(Serie & Bartonek 1991a) and maximum
counts of > 210,000 Tundra Swans in North
America were recorded in 1999 (228,818
birds) and 2003 (210,923 birds; Fig 2b).
Numbers have since declined a little, with the
most recent combined total being of 186,825
swans counted in 2017. The EP averaged at
c. 70,800 ± 3,300 and the WP at 102,500 ±
10,800 in the 5 years from 2013 to 2017 with,
despite marked annual fluctuations, both
populations seeming relatively stable in the
long term (from 1990 onwards; Fig. 2b).
The number of Tundra Swans harvested
each year is also monitored, and regulated
under provisions of the Migratory Bird
Treaty Act of 1918 (Serie & Bartonek 1991b).
Mean numbers taken each year over the
1990–2017 period are of 4,825 (WP) and
3,730 (EP) (Fig. 2c), with monitoring
indicating that this is not causing either
population to go into decline (Fig. 2b).
Threats and conservation issues
Monitoring of migratory swans in North
America is undertaken with the aim of
meeting conservation and management
objectives set by the Pacific, Central and
Mississippi Flyway Councils for both species.
For the Trumpeter Swans, these are to
maintain 25,000 total swans (white birds
and cygnets) in the PCP and to have “at least
2,000 birds and 180 successful breeding pairs by
2001” in the IP; objectives now met for
both populations. For the RMP, whilst
overall abundance objectives have also been
achieved, regional objectives relating to
abundance, distribution and the number of
breeding pairs have been met in some areas
but not others (Groves 2017). Overall, the
recovery in Trumpeter Swan numbers from
the 69 birds recorded during the early 20th
century is considered a major conservation
success story, and the species continues
to be in good conservation status with
numbers increasing for all three populations.
There are also currently no plans for an
open hunting season for Trumpeter Swans,
although a very limited take is permitted to
allow for accidental hunting of Trumpeter
Swans in Tundra Swan hunts, estimated at c.
2.1% of the Tundra Swan harvest (Drewien et
al. 1999). There is concern, however, over
plans to amend guidelines for interpreting the
Migratory Bird Treaty Act (MBTA) of 1918,
and its strict prohibition on the unregulated
killing of birds, which has been one of the
guiding documents for avian protection in
North America since the early 20th century.
Specifically, a legal memorandum by the U.S,
Department of the Interior has changed a
long-held interpretation on what constitutes
“incidental take”, and the change has
profound implications for many migratory
birds, including swans, in North America
(Mitchell 2018). How closely Tundra Swan
bags are currently inspected for Trumpeter
Swans is unclear, and the source of
Trumpeter Swans harvested in Tundra Swan
hunts is also not known. Thus, although
population growth rates indicate that
incidental harvest is unlikely to cause a decline,
there is concern that incidental harvest of
Trumpeter Swans in some places (e.g. Utah)
might remove “pioneering” swans dispersing
into a region and consequently slow range
expansion. Incidental take could also include
mortality from environmental contamination
Conservation status of the world’s swan populations 45
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(e.g. from mining, use agricultural chemicals,
etc.), which is now prevalent in the Tundra
and Trumpeter Swans’ migratory ranges (e.g.
Blus et al. 1999; Parsons et al. 2010).
Following increases in North America
during the mid-20th century, Tundra Swan
numbers are now limited by hunting, and
desired population levels and distributions
have been described in management plans.
Harvest objectives for both EP and WP
hunt plans are to harvest the optimum
allowable number of swans each year whilst
maintaining populations at satisfactory levels
to meet goals of the various management
plans. A 10% harvest rate of the three-year
average winter population index was
established as an initial guide until more
definitive data became available, and if the
three-year average winter population index
for EP and WP Swans fell below 60,000 and
40,000, respectively, season closures were to
be considered (Serie & Bartonek 1991b). The
10% harvest rate was reduced to 5% in 1996
to stimulate population growth (Serie et al.
2002), and numbers are consistently above
the population target levels.
Eurasia (migratory swans)
Whooper Swan
The Whooper Swan breeds across the
boreal zone of Eurasia, from Iceland to
Kamchatcka, and five main populations
have been described: the Icelandic,
Northwest Mainland Europe, Black Sea/
East Mediterranean, Caspian/West Siberian
and East Asian populations, with some
overlap in distribution considered likely to
occur in the wintering ranges (Rees 2005;
Wetlands International 2019a; Fig. 3a). The
extent of population interchange is not
known. Ringing of Whooper Swans since the
early 1980s, and more recent satellite-tracking
of individual birds, have shown that although
the vast majority of the Icelandic population
winters in Britain and Ireland a few individuals
migrate to continental Europe (e.g. Garðarsson
1991; Newth et al. 2007; Griffin et al. 2011).
Conversely some from the Northwest
Mainland European population (marked in
Finland) have migrated to southeast England,
but their numbers are thought to be low
(Laubek 1998; Hall et al. 2016).
Coordinated international censuses of
migratory swans, undertaken at 5-year
intervals across Europe, have estimated the
total population size and trends in numbers
for the Icelandic population since 1986
and the Northwest Mainland European
population since 1995 (Hall et al. 2016;
Laubek et al. 2019). Both populations have
more than doubled in numbers since the
censuses commenced, and estimates of
c. 34,000 for the Icelandic population and
c. 138,500 for the Northwest Mainland
European population in 2015 are the highest
recorded to date (Hall et al. 2016; Laubek
et al. 2019; Fig. 3b). Much less is known
regarding the other three Whooper Swan
populations, but trends analysis and
population estimates for the Black Sea/East
Mediterranean population, undertaken by
Wetlands International in 2015, updated the
previous estimate of 12,000 swans dating
back to 1983 to c. 14,000 individuals based
on IWC totals of 3,000–7,000 individuals
counted in the region between 2011–2015
(Rüger et al. 1986; Wetlands International
2019b,c). Trends statistics indicated a strong
increase in numbers in the long-term (1989–
46 Conservation status of the world’s swan populations
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160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
0
1970
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
Population estimate (no. swans)
Year
NW Mainland Europe
Iceland
Black Sea/East Med
Caspian/W Siberian
East Asian
Figure 3. Whooper Swans: (a) distribution and (b) population estimates (from Miyabayashi &
Mundkur 1999; BirdLife/Wetlands International 2018; Laubek et al. 2019; Wetlands International
2019a).
(a)
(b)
Conservation status of the world’s swan populations 47
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
2015) but more recent trends (2006–2015)
are uncertain, with large year-to-year
fluctuations and gaps in coverage recorded
(Wetlands International 2019c). Numbers in
the Caspian/West Siberian population were
estimated at c. 20,000 in 1996 (Scott & Rose
1996; Wetlands International 2019a), and
analysis of IWC count totals which varied
markedly from 100–17,000 individuals
between 2011–2015 (with low counts
probably reflecting a lack of coverage in some
years) retained the population estimate of
20,000 birds (Wetlands International 2019c).
Main wintering grounds for the species in the
northern part of the Caspian Sea were not
monitored, however, and weather conditions
cause shifts in distribution between years,
which may potentially also result in movement
to the Black Sea/East Mediterranean
wintering areas. Both the short-term (10-year)
and longer-term (25-year) trends therefore
were classed as “uncertain”.
The population estimate of 60,000 birds
adopted by Wetlands International for the
East Asian Whooper Swan population,
which dates back to 1999 (Miyabayashi &
Mundkur 1999), was a marked increase on
the 30,000 in 1995 reported by Rose & Scott
(1997), but the change was more likely
attributable to improved monitoring of
Whooper Swans in the region rather than a
doubling in numbers over a 5-year period.
More recently, a study summing Whooper
Swan counts from South Korea, Japan and
China (i.e. covering most of the wintering
range for the population, except perhaps for
swans wintering in the D.P.R. of Korea)
suggested that the population size was lower,
with 49,700 swans counted in 2006 and
41,800 in 2011 (Jia et al. 2016). Trends
analyses have not been undertaken for the
East Asian Whooper Swan population as a
whole, but mid-January counts made of
Whooper Swans in Japan from 1970
onwards indicate that numbers wintering in
the country increased from 11,095 recorded
during the first census to an average of
31,000 during 1995–1999 (Albertsen &
Kanazawa 2002). More recently, national
totals have been stable at an average of
31,262 (s.d. ± 4,092) swans counted annually
from 2000–2017 inclusive (Ministry of the
Environment 2018); maximum numbers
recorded in Japan to date are of 38,660 birds
in 2006, with the most recent count (made
in 2017) a little below that at 29,741
birds (Ministry of the Environment 2018;
T. Shimada, pers. comm.). Given that Japan
appears to receive a high proportion of the
East Asia Whooper Swans in mid-winter, it
seems that the trends for East Asian
Whooper Swans are currently stable, but
in the absence of regular internationally
coordinated counts to monitor numbers and
shifts in distribution between wintering areas
in Russia (Kamchatka Peninsula), China,
Japan, D.P.R. Korea (North) and the
Republic of Korea (South) (Miyabayashi &
Mundkur 1999), this remains speculative.
The combined number of Whooper
Swans globally therefore is currently
estimated at 266,543 birds, with the majority
(56%) in the Northwest Mainland European
population (Table 1; Fig 3). Several of the
flyway population totals are based on
analyses of IWC data however, which are
thought to underestimate numbers for at
least the Northwest Mainland Whooper
Swan population (Laubek et al. 2019), and
this might be the case for other populations
48 Conservation status of the world’s swan populations
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(or even species) also, so further count data
are required to confirm numbers and overall
trends for Whooper Swans globally.
Bewick’s Swan
Bewick’s Swans breed at high latitudes
across the Russian arctic tundra from
Cheshskaya Bay in the Nenets Autonomous
Okrug (NAO) in the west to Chaun Bay,
Chukotka, in the east, and extending north
to Kolguev Island, Vaygach Island, Novaya
Zemlya and the Lyakhovskiy Islands of the
New-Siberian Archipelago (Rees 2006).
Three main populations have been described:
the Northwest European population breeds
in European Russia (west of the Urals) and
winters in northwest Europe, the Caspian
population winters primarily around the
Caspian Sea, and the Eastern population
migrates to China, Japan and Korea (Fig 4a).
Recent tracking studies suggest that Bewick’s
Swans breeding in Chukotka and wintering
in Japan actually may be sufficiently discrete
to be considered a separate subpopulation
or a fourth population (e.g. Wang et al. 2018).
As for the Whooper Swans in Europe,
trends in the numbers and distribution of
the Northwest European Bewick’s Swan
population have been monitored through
the IWCs since the mid-20th century (Nagy
et al. 2012), verified by coordinated 5-yearly
mid-winter censuses of the species from
January 1984 onwards (Beekman et al. 2019).
Following an increase in the Northwest
European population during the 1980s to
mid-1990s, there was a 39% decline in
numbers between 1995–2010, which led to
an International Single Species Action Plan
being adopted by AEWA (Nagy et al. 2012;
Fig 4b). The 2015 coordinated census
suggested a slight recovery to 20,100 birds
in 2015, but the next census (scheduled for
January 2020) should determine whether the
decline is reversed or ongoing (Beekman et al.
2019, with Wetlands International trends
analyses for the most recent 10-year period
(2006–2015) showing the population to be in
steep decline (Wetlands International 2019c).
The Caspian population is receiving
increasing attention, particularly regarding
its contribution to numbers wintering on
the Evros/Meriç Delta in Greece/Turkey,
where peak counts rose from 10 in the
early 2000s to c. 8,400 by 2016 (Vangeluwe
et al. 2018). Population size was estimated
at 500–1,000 in the late 20th century so,
although Syroechkovski (2002) considered
this to be an underestimate because of the
difficulty in separating Bewick’s from
Whooper Swans Cygnus cygnus overwintering
in the northern part of the Caspian Sea, if
swans in Greece/Turkey emanate mainly
from the Caspian area, most had previously
been missed and/or there has been a
significant increase in population size (Rees
& Rozenfeld accepted, European Breeding
Bird Atlas 2nd edition). Even on omitting
Greece, there is good evidence from
Wetlands International’s analyses of the
IWCs for a strong increase in the Caspian
population since the start of the 21st
century (particularly since 2010), with c.
800–3,000 individuals counted annually in
the region between 2011–2015 inclusive
(Wetlands International 2019c).
For many years relatively little was known
regarding the status of Bewick’s Swans in
the Eastern population, primarily because a
lack of data from China, and numbers were
put at around 40,000 birds during the late
Conservation status of the world’s swan populations 49
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180,000
160,000
140,000
120,000
100,000
80,000
60,000
40,000
20,000
0
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
Population estimate (no. swans)
Year
NW Europe Caspian Eastern
Figure 4. Bewick’s Swans: (a) distribution (from Rees & Beekman 2010) and (b) population
estimates (from Jia et al. 2016; Beekman et al. 2019; Wetlands International 2019a; L. Cao, pers.
comm.).
(a)
(b)
50 Conservation status of the world’s swan populations
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20th century. These included an estimated
10,000 in China, 20 in D.P.R. Korea and
26,000 in Japan, with numbers in the
Republic of Korea having declined from a
high of 1,300 in 1992 to 156 in January 1999
(Miyabayashi & Mundkur 1999). Surveys of
the Yangtze River floodplain initiated in 2004–
2005, and still ongoing, found substantial
numbers in China (Barter et al. 2006; Cong et
al. 2011; Jia et al. 2016), however, resulting in
a major upward revision in population size
estimates for the Eastern Bewick’s Swan
population. Annual waterbird censuses made
in Japan found that numbers of Bewick’s
Swans wintering in the country increased
steadily during the second half of the 20th
century, from just 542 birds counted in 1970
to 31,198 in 1996 (Albertsen & Kanazawa
2002), after which the growth rate slowed,
but a maximum count of 45,283 was recorded
in 2004. Although numbers in Japan declined
thereafter, with 35,596 recorded in 2017, they
seem to be relatively stable at 37,116 (s.d. ±
5,833) between 2000–2017 (Ministry of the
Environment 2018). Because the timing of
national censuses are not coordinated across
the wintering range, fluctuations in numbers
counted in China which may reflect a shift in
winter distribution. Also, given the threats to
swans at Chinese wintering sites (e.g. illegal
harvesting and habitat loss; Ma & Cai 2002),
it is still not possible to be certain about
the stability of the Eastern population.
Nonetheless, summing uncoordinated counts
made in the key wintering areas of China
and Japan over the past two decades indicates
that numbers reached 169,800 in 2006, and
148,300 in 2008, but more recently have
been estimated at c. 90,000 in 2017 (35,596 in
Japan; c. 55,000 in China; Ministry for the
Environment 2018; Cao Lei, pers. comm.;
Fig. 4b), with the trend put as “fluctuating”
(Table 2).
Overall, Bewick’s Swan numbers are
estimated at around 120,000 globally, with
the proportion of swans wintering in Greece
that follow the Northwest European versus
the Caspian flyways yet to be determined.
Recent tracking of swans fitted with GPS
loggers on the Yamal Peninsula have also
described previously unknown migration
routes to central Asia (Vangeluwe et al. 2018),
and further surveys are required to determine
the numbers wintering at these sites.
Threats and conservation issues
Whooper Swans and Bewick’s Swans have
very similar distributions across Eurasia and,
although Whooper Swans generally breed at
lower latitudes and few Bewick’s Swans winter
in Poland, eastern Denmark and Sweden,
mixed species flocks frequently occur in major
parts of the wintering range. The question of
whether increasing numbers of the larger and
generally more dominant Whooper Swans are
having a detrimental effect on Bewick’s Swan
populations therefore is being considered,
particularly given that they utilise similar
food resources during winter. There was no
evidence for food resources limiting use of an
internationally important wintering site for
both species in Britain, however, and there
was also no evidence for Bewick’s Swan body
condition varying in line with trends in
population size over the decades (e.g. Wood et
al. 2018, 2019a,b).
Both species are legally protected from
hunting across most of their range. Although
protection levels for Whooper Swans are
lower than for Bewick’s Swans in parts of
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Russia (Newth et al. 2019), there is not an
open season analogous to that for Tundra
Swans in North America. There is illegal
hunting of both species, however (Newth
et al. 2011), and this likely occurs in different
populations, albeit to a greater extent for
some than for others depending on variation
in hunting intensity along different migration
routes. For instance, x-raying of live-caught
swans wintering in Britain found that the
proportion of birds with embedded shotgun
pellets was consistently higher for Bewick’s
Swans (34.1% in the 1970s, 38.8% in the
1980s, 27.1% in the 1990s and 22.7% in the
early 2000s respectively) than for Whooper
Swans (14.9% with pellets in the 1980s;
13.2% in the 2000s; Newth et al. 2011).
The apparent decline in the proportion of
Bewick’s Swans being shot at a time when the
population was in decline suggests that
hunting per se was not the only reason for
the decline in the Northwest European
population from the mid-1990s. However,
given the high proportion of Bewick’s Swans
sampled found to have been shot at, a
reduction in illegal hunting should help
towards recovery of the population, not least
because during the 2010s the proportion of
swans with embedded pellets has returned to
higher levels typical of the 1970s–1980s
(WWT unpubl. data; J. Newth pers. comm.).
Whilst Whooper Swan numbers are
increasing in northwest Europe, the status
of three of its populations – the Black Sea/
East Mediterranean, Caspian/West Siberian,
and East Asian populations – remain poorly
known, largely because of difficulties in
making comprehensive surveys in areas
without the benefit of ornithological
count networks. Moreover, Bewick’s Swan
populations currently seem to be in a state
of flux, with population declines in some
areas and increasing numbers in others,
and the extent to which the different
demographic variables (survival/productivity/
emigration/immigration) are responsible,
and whether the changes are attributable to
climate and other environmental factors
trends, has yet to be determined. Changes in
demography and migration routes do
however seem likely to vary in relation to the
differing conditions encountered by the
swans across Eurasia.
Mute Swan
The Mute Swan is native to Europe and
Asia, where it ranges from Ireland in the
west to China in the east, and has the most
southerly breeding range of all Eurasian
swans (Rowell & Spray 2004; Fig. 5). Non-
native populations have also become
established, through introduction programmes
or accidental releases, particularly in North
America, Japan, Australia and New Zealand,
with smaller numbers occurring in Mauritius,
South Africa and the United Arab Emirates
(Gayet et al. in press). Even in central and
western Europe, breeding and release of
Mute Swans in several countries from the 16th
century onwards means that it is not always
possible to distinguish between wild and
introduced stocks (Gayet et al. in press), so we
do not attempt to separate them further here.
Seven Mute Swan populations have been
described for Eurasia, in: Ireland, Britain,
Northwest Mainland & Central Europe,
Black Sea, West & Central Asia/Caspian,
Central Asia and East Asia (Wetlands
International 2019a). Population delineation
is not well established, though ring re-
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Table 2. Current population estimates and trends for swan species globally. INC = increasing; DEC = decreasing; STA = stable;
UNC = Uncertain; ? = general trend indicated, but this uncertain. aNumbers of Bewick’s Swans in the Caspian population may be
underestimated if the majority of the c. 8,400 birds counted in February 2016 (Litvin & Vangeluwe 2016) are from this population.
Species Population Current Year of 25-year 10-year Source
estimate estimate trend trend
Trumpeter Swan Pacific Coast 31,793 2015 INC INC Groves 2017
Rocky Mountain 17,164 2015 INC INC Groves 2017
Interior > 27,005 2015 INC INC Groves 2017
Tundra Swan Western 71,400 2017 INC STA Olsen 2017
Eastern 115,425 2017 INC STA Roberts & Padding 2017
Whooper Swan Icelandic 34,004 2015 INC INC Hall et al. 2016
NW Mainland Europe 138,448 2015 INC INC Laubek et al. 2019
Black Sea/East Med 14,000 2015 INC INC? Wetlands International 2019b,c
Caspian/W Siberian 20,000 2015 UNC STA/FLU Wetlands International 2019b,c
East Asian 42,000 2011 UNC STA? Jia et al. 2016
Bewick’s Swan NW European 20,148 2015 DEC DEC Beekman et al. 2019
Caspiana3,000 2015 INC INC Wetlands International 2019b,c
Eastern 90,000 2017 FLU FLU Jia et al. 2016; this paper
Conservation status of the world’s swan populations 53
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Table 2 (continued).
Species Population Current Year of 25-year 10-year Source
estimate estimate trend trend
Mute Swan Ireland 9,130 2016 DEC STA Burke et al. 2018
Britain 50,000 2019 INC STA Frost et al. 2019; Wood et al. 2019c
NW Mainland & 250,000 2019 INC INC/STA This paper
Central Europe
Black Sea 49,000–72,000 2015 STA? STA? Wetlands International 2019b,c
West & Central 250,000 2015 INC? INC? Wetlands International 2019b,c
Asia/Caspian
Central Asia 10,000 1993 UNC UNC Wetlands International 2019c
East Asia 3,000 1999 UNC UNC Miyabayashi & Mundkur 1999;
Wetlands International 2019c
Black Swan Australia 165,000–180,000 2008 STA? STA? This paper
Black-necked South America 25,000–100,000 1990–2000 UNC UNC Wetlands International 2019a
Swan Falkland Islands 750–1500 1990–2000 STA? UNC Wetlands International 2019a
Coscoroba South America 10,000–25,000 2006 UNC UNC Wetlands International 2019a
Swan
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sightings suggest that there is relatively little
movement between the Irish, British and
Northwest Mainland European populations
(Fransson & Pettersson 2001; Spray et al.
2002; Bakken et al. 2003; Bønløkke et al.
2006). The species is generally more
abundant, and estimates of population
size and trends are therefore made more
sporadically than for the migratory swans of
the northern hemisphere.
The history of the Mute Swan in Ireland
is poorly understood; introduced birds were
known to be present in the 1700s, but
whether the species also occurred there in
the wild seems unclear (Rowell & Spray
2004). The first comprehensive monitoring
of waterbirds in Ireland was undertaken in
the early 1970s, and a follow-up survey was
carried out over a decade later in winters
1984/85–1986/87, at which time the Mute
Swan population for Ireland was estimated
at 10,000 birds (Sheppard 1993). A long-
term monitoring programme, the Irish
Wetland Bird Survey (I-WeBS), commenced
winter 1994/95 and counts of 5,200–6,000
in 1995 and 1996 for this widely scattered
species resulted in the population estimate
of 10,000 birds being retained (Delany et al.
1999). The 1988–1991 Breeding Birds Atlas
project in Britain and Ireland suggests that
Figure 5. Distribution of native Mute Swan populations (from BirdLife International and Handbook
of Birds of the World 2016). “Summer distribution” of Northwest Mainland and Central European
Mute Swans in European arctic Russia (with arrows indicating possible autumn migration routes) is
based on regular observations and recent ringing of the species during moult within the Nenetskiy
National Okrug (WWT and Nenetskiy zapovednik, unpubl. data). The route taken between summering
and wintering is not known, but one ringed individual was re-sighted in Hungary in mid-winter and a
second in the Kuzhenerskiy district of Russia c. 1,000 km south of the ringing site. Overlapping ranges
are where population boundaries/interchange are poorly understood.
Conservation status of the world’s swan populations 55
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the Irish population may have been higher
(19,000–20,000 birds) than previously
supposed (Ogilvie & Delany 1993). Trend
indices for Northern Ireland determined
through the UK’s Wetland Bird Survey
(WeBS) showed an increase from the mid-
1980s to the early 2000s (Rowell & Spray
2004), and the Irish population as a whole
was estimated at 11,440 during 1994/95–
2003/04 (Crowe et al. 2008). Continued
annual monitoring of waterbirds through
the I-WeBS and WeBS schemes has more
recently estimated Mute Swan numbers at
9,130 (7,032 and 2,094 in the Republic and
Northern Ireland respectively) for winters
2011/12–2015/16, representing a long-term
decline in numbers (put at 24.9%) since the
mid-1990s (Burke et al. 2018).
It has been suggested that the Mute Swan
was introduced to Britain by the Romans
and, although archaeological evidence
indicates that the species was widespread
much earlier throughout Britain (Yalden
& Albarella 2009), the Romans may have
instigated its domestication, as the species
was being kept in a semi-domesticated state
for food by the 11th century (Birkhead &
Perrins 1986; Rowell & Spray 2004). At one
time the Crown claimed possession of all
the Mute Swans in England, but over time
ownership rights for swans were granted to
the clergy and local noblemen in certain
areas. By the late 19th century swan-keeping
had declined, and the wild population
increased as a result of escapes from semi-
domestic flocks (Birkhead & Perrins 1986).
Mute Swans were of conservation concern
in Britain in the mid-20th century, as lead
poisoning mortality caused by the birds
ingesting spent lead fishing weights whilst
foraging for grit reduced the population to
17,600 in 1978. Numbers increased steadily
following legislation in January 1987,
banning the use of weights with sizes
deemed most likely to be ingested by swans
(0.06–28.35 g), to an estimated 74,000 birds
for winters 2004/05–2008/09 (Musgrove
et al. 2013) with population growth
stabilising at around this time (Wood et al.
2019c). Frost et al. (2019) recently put
numbers lower, at 50,000 birds, but this was
attributed to a methodological change in
the approach used to estimate numbers,
involving environmental stratification
(considered more accurate for this species),
rather than a real decline in population size.
Less is known about the other Mute Swan
populations in Eurasia, although trends
analyses of IWC data found a strong long-
term (1972–2015) increase in the Northwest
Mainland & Central European population.
Short-term (2006–2015) trends are given as
uncertain/stable, and IWC count totals were
of 132,000–200,000 individuals between
2011–2015, resulting in a total population
estimate of c. 250,000 birds (Wetlands
International 2019c). In CSR 7 the population
size was however based on a breeding
population of 57,821 to 80,792 pairs in
the 24 countries within the flyway, which
multiplied by three gave a population
estimate of 173,000–243,000 birds and a
resulting 1% criterion of 2,000 birds, a 20%
downscale from the 2,500 birds that had
been published in WPE 3, 4 and 5 (Wetlands
International 2019a). Estimating population
size and trends for a long-lived species only
from the size of its breeding population
is problematic, however, as the approach
assumes that breeding pairs have an average
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of one cygnet surviving to winter, and
ignores the fact that there is a large non-
breeding bird component that aggregates
to moult during the breeding season. In
Denmark alone, the last two national censuses
of moulting swans both recorded 50,000
birds in 2006 and 2012 (Nielsen et al. 2019)
and, although Denmark probably hosts
most moulters (given that many birds from
Poland, Germany and the Netherlands fly
to moult in the country; Bønløkke et al.
2006), flocks of thousands are also known
to moult in the Netherlands and Germany
(Blüml & Degen 2009; Sellin 2013; Hornman
et al. 2016). The data source for the breeding
population estimate was the European
Union Birds Directive Article 12 dataset for
2008–2012, supplemented with Birdlife
International (2015) European Red List data
for countries outside EU. Unfortunately, only
seven of the 24 flyway countries potentially
holding Mute Swans from the Northwest
Mainland & Central European population
had submitted wintering population totals,
summing to 158,000–186,000 birds. Two
major wintering countries had not reported
their numbers, notably Sweden where 50,500
birds were recorded wintering in 2015 (Nilsson
& Haas 2016) and the Netherlands with
28,000 in the same year (Hornman et al.
2016), whilst other non-listed countries are
likely to add some thousands each, e.g. Austria
(average count = 2,770 for the period 1970
to 2014, but with the latter year being near
the average, judged from an index figure;
Teufelbauer et al. 2015), Switzerland (6,623
and 7,334 in 2015 and 2016, respectively;
Strebel 2016) and the Czech Republic (3,000–
4,000 wintering in 2009–2013; Musilova et al.
2014). Hence, in line with the “increasing-
stable” population trend indications for
2000–2015 (Wetlands International 2019a), it
is clear that the population has not declined,
but more likely increased. We therefore
maintain the previous estimate of 250,000
birds, and call for a more comprehensive
review where data from the same (or at least
adjacent) wintering years are compiled,
because we believe that the winter counts give
a better estimate for the population size.
The West & Central Asia/Caspian
population is also considered to be abundant,
with the population put at c. 250,000
individuals from IWC count totals of
c. 500–31,000 individuals between 2011–
2015. Trend analysis for the population was
based on data from just four countries
(particularly Turkmenistan and Iran; also
Azerbaijan and Kyrgyzstan) and both long-
and the short-term trends were classed
as “uncertain” due to large year-to-year
fluctuations and missing data (Wetlands
International 2019c). The Black Sea
population was put at 45,000 in the mid-
1990s (Scott & Rose 1996) and more recent
assessment of IWC count totals (c. 11,000–
22,000 individuals counted each year between
2011–2015) again estimates that the
population is of c. 45,000 birds. Both long-
term (1998–2015) and short-term (2006–
2015) trends are classed as “uncertain”
because of large year-to-year fluctuations
and missing data, particularly from the
Ukraine (where larger numbers are known
to winter, e.g. Scott & Rose 1996), but
with an overall declining tendency in the
long term, though more stable in the short
term (Wetlands International 2019c).
Further east, much better information is
also needed on the Central Asian and the
Conservation status of the world’s swan populations 57
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
East Asia populations of Mute Swans,
which have been estimated at 10,000 and
1,000–3,000 birds respectively since the 1990s
(Wetlands International 2019a; Table 2).
Total numbers of Mute Swans in areas
where the species is native are therefore put
at c. 642,000 (Tables 1 & 2), although given
the gaps in coverage this is likely to be an
underestimate. Moreover, Mute Swans from
introduced populations occur, most notably
in North America where c. 13,000 were
recorded in 1993 (Ciaranca et al. 1997) with
numbers increasing since then to c. 50,000–
60,000 birds (review in Gayet et al. in press),
although given population control measures
in the region these recent figures require
verification. An estimate of 17,520 individuals
in Michigan in 2013 (D. Luukkonen, unpubl.
data) made it the largest Mute Swan
population in North America, though
recently finalised management goals and
objectives of the Michigan Department of
Natural Resources are for there to be no
more than 2,000 Mute Swans in Michigan
by 2030 (Michigan Department of Natural
Resources 2012; Knapik et al. 2019).
Elsewhere introduced Mute Swan populations
have remained relatively limited in numbers,
with only 200–300 birds occurring in each
of Japan (up to 367 in 2017), New Zealand
and Australia (del Hoyo et al. 1992; Ministry
for the Environment 2018), and several
formerly introduced populations (in Iceland,
South Africa and the United Arab Emirates)
have now disappeared (Gayet et al. in press).
Threats and conservation issues
The Mute Swan is protected across most of
its range in Europe under Annex II of the
European Bird Directive (Directive 2009/
147/EC), according to which the species
can only be hunted potentially in Germany
and Austria, where numbers are increasing,
although culling is sometimes practised
under licence in relation to crop damage in
other countries (e.g. the Netherlands), even if
damage is not always proven (Esselink &
Beekman 1991). Non-lethal control measures
such as fencing and other deterrents are used
to keep birds away from some areas and
illegal shooting of Mute Swans is known to
have occurred in the UK because of perceived
damage to valuable habitat at salmonid
fisheries (review in Gayet et al. in press).
Although increasing Mute Swans numbers
can have some negative effects within its
native range, this seems to be a particular
issue in North America where it is
considered an aggressive non-native invasive
species, and deleterious effects are reported
as including depletion of aquatic and
agricultural vegetation and displacement of
other waterbirds (e.g. Tatu et al., 2007;
Stafford et al. 2012). A combination of
population control actions, including public
education, culling of adult swans and egg-
oiling, therefore have been used to reduce
the number of Mute Swans at Chesapeake
Bay in Maryland (from 3,995 individuals in
1999 to 41 in 2014; Hindman et al. 2016a,b,
2018), and to stabilise abundance at c. 9,000
birds in Michigan (Arsnoe & Duffiney 2018;
Gayet et al. in press).
Australasia
Black Swans
Black Swans are endemic to Australia, where
they occur across the whole continent except
for central and northern regions (Fig. 6a),
1,000
800
600
400
200
0
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
No. swans
Year
58 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
Figure 6. Black Swans: (a) distribution in Australia (based on Kingsford et al. 2011), (b) maximum
counts recorded in Tasmania (based on Gaffney 2019) and (c) maximum counts recorded in south
Queensland (J. Coleman, unpubl. data).
25,000
20,000
15,000
10,000
5,000
0
1985 1987 1989 1993 1995 1997 1999 2001 2003 2007 2009 2011 20131991 2005
No. swans
Year
(a)
(b) Tasmania
(c) South Queensland
Conservation status of the world’s swan populations 59
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
and are one of the most abundant species
recorded during continent-wide waterbird
censuses (Kingsford et al. 2011). Monitoring
Black Swan numbers therefore is undertaken
only occasionally, and population estimates
are thus less precise than for some of the
other swan species, but the estimate of
100,000–1,000,000 birds given in the WPE
(Wetlands International 2019a) seems
particularly wide-ranging. The most recent
census of 136,005 Black Swans recorded via
aerial surveys during the national waterbird
survey of Australia in 2008 was incomplete
(Kingsford et al. 2011), but with an
estimated 70–80% of the population
covered (R. Kingsford, pers. comm.) a total
population estimate of 165,000–180,000
based on these counts is towards the lower
end of the range given in the WPE.
Numbers are generally thought to be stable
since the late 20th century, but habitat loss
due to inland river regulation and coastal
development probably may inflict some
long-term decline (Wetlands International
2019a). Annual waterbird surveys conducted
at 76 wetlands in Tasmania indicate that
numbers there fluctuated markedly between
c. 1,000–24,000 birds over the period
1985–2018, but the trend was generally
stable (Gaffney 2019; Fig. 6b). More recent
count data collected in a study area in
southeast Queensland (Coleman 2014)
shows similar variability in numbers, but
overall again demonstrated a stable trend
over time between 2007–2019 inclusive (J.
Coleman, unpubl. data; Fig. 6c).
A Black Swan population is also
established in New Zealand following
introductions in the 1860s, though recent
molecular and morphometric studies of
fossil remains indicate that a potentially
distinct Cygnus sumnerensis, divergent from
modern (Australian) Black Swan C. atratus,
was present at the time of human colonisation
(Rawlence et al. 2017). The national population
was put at c. 50,000 in 2011; it was formerly
more numerous, but widespread loss of
aquatic plants from most lowland lakes greatly
reduced their numbers (Williams 2013).
Black Swans have also been introduced to
European countries for ornamental purposes,
but their numbers have not expanded to the
extent observed in New Zealand, or for
Mute Swans in North America.
Threats and conservation status
Black Swans are fully protected in all states
in Australia, and are not subject to active
control measures. Although regular counts
are lacking, numbers are probably declining
in river basins subject to water resource
development (e.g. the Murray-Darling Basin;
Kingsford et al. 2017). Reductions in flows
and innundation of wetlands (Kingsford
2000) is a serious threat to Black Swan
populations. Breeding distribution and
timing is influenced by appearance of
ephemeral wetlands, and as such the species
is sensitive to drought conditions.
In New Zealand, where the Black Swan is
non-native, it is a quarry species with up to
7,000 shot in 2011. The loss of aquatic
vegetation (the preferred food for this
species) in recent years has seen the
population go into decline (Williams 2013).
South America
Black-necked Swans
The total number of Black-necked Swans,
which occur in the southern part of South
60 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
America, is also not known. A combination
of national and regional counts puts the
total at < 100,000 in the mid-1980s to mid-
1990s, of which 20,000 were thought to be
in Chile, 50,000 in Argentina, at least 20,000
in Uruguay, 2,000–3,000 in southern Brazil
and 750–1,500 on the Falkland Islands
(Schlatter et al. 1991a; Rose & Scott 1997;
Rees 2005). More recent estimates, for the
period 1990–2000, are of 25,000–100,000
on continental South America and 900–
1,800 on the Falkland Islands (Wetlands
International 2019a), at which time numbers
were considered to be stable. Counts made
in southern Chile (including northern
Patagonia and the Araucanian Lake District)
estimated 25,000 Black-necked Swans in the
region during the 1990s, with c. 10,000 on
Chiloé Island and similar numbers colonising
areas to the north of Chiloé, between
Chacao Channel and Budi Lake (Schlatter et
al. 2002). Numbers at the Carlos Anwandter
Sanctuary, a Ramsar Site on the Cruces River
in Chile, increased over the period 1985–
2000 from 640 in 1985 to a peak of 14,533
in 1997, but with marked variation in numbers
associated with rainfall events (Schlatter et al.
2002). Loss of aquatic vegetation at the
site, however, resulted in numbers rapidly
declining to just a small number of
individuals present in 2000–2004, before
recovering to 6,000–7,000 in 2017 (Vilina &
Flores 2017; Jaramillo et al. 2018).
The species does not undertake seasonal
long-distance migrations in the manner
of the migratory swans of the northern
hemisphere but redistributes in response to
local conditions. A sharp increase, from 2,178
to 6,426 birds in Chile between January and
late May 1989 was attributed to immigration,
resulting from climatic drought in Argentina
(Schlatter et al. 1991). Vilina and Cofre
(2018) report that during dry periods in
central Chile, waterbirds can mainly be found
in the southeast coastal wetlands, which
could explain the occasional recording of
20,000 Black-necked Swans and 1,000–2,000
Coscoroba Swans on Seno Ultima Esperanza
in Puerto Natales (51°28’S, 73°06 W), in the
Magallanes region (Vuilleumier 1997).
The current status of Black-necked Swans
is unclear, but it is thought that they are now
likely to be in decline because the species is
vulnerable to high mortality during severe
droughts associated with ENSO (El Niño –
Southern Oscillation) events (Schlatter et al.
2002), such as the droughts of 1998–99 and
the central Chile mega-drought of 2010–
2015 (Garreaud et al. 2017; Y. Vilina, pers.
comm.).
Coscoroba Swan
As for the Black-necked Swan, the number
of Coscoroba Swans is unclear. It occurs
slightly further south (Fig. 7a,b) and in Chile
it was mainly found in Patagonia during the
mid-20th century. In general, it has a
patchier distribution than the Black-necked
Swan, making it more difficult to assess total
numbers and trends in abundance. Moreover,
although it frequents lowland sites, it also
occurs on Andean lakes at up to 1,000 m
(Rees & Brewer 2005). In 1994 it was
recorded for the first time at the El Yali
wetland, almost 1,500 to the north of its
previous breeding range within Chile, in the
“Mediterranean, Forests, Woodlands and
Scrub” biome (World Wide Fund for Nature
classification; Vilina 1994), and has since
extended to breed at several other wetlands
Conservation status of the world’s swan populations 61
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
in this ecoregion (Brewer & Vilina 2002;
Silva-García & Brewer 2007).
Trends in numbers were considered stable
in the late 20th century and the species was
estimated at 10,000–25,000 in 2006, roughly
equating to 6,700–17,000 mature individuals
(Wetlands International 2019a; BirdLife
2019b). The species only occasionally occurs
on the Falkland Islands; successful breeding
by a pair on Pebble Island in 2000/01 was the
first breeding record for Coscoroba Swans
in the archipelago since 1860 (Wetlands
International 2019a).
Threats and conservation status
The conservation status of South America’s
swan species is not well known and their
population ecology (habitat requirements;
movements) is poorly understood in
comparison with some of the other swan
species. The lack of coordinated count
programmes within and across countries
means that species abundance and trends in
numbers are unclear, although both species
are considered susceptible to the rapid loss of
wetland habitat associated with more frequent
drought events in recent years (Y. Vilina,
pers. comm.). Ringing and re-sightings studies
are required to provide a better understanding
of movements of swans in South America,
for instance to determine whether the Andean
Mountains restrict east-west movements (and
vice versa) for both species, and thus assess
whether relatively discrete populations exist.
Ringing of Black-necked Swans has recently
been initiated at the Carlos Anwandter
Sanctuary on the River Cruces in south-
central Chile and it is hoped that resightings
will provide information on the swans
movements and survival rates. Given the
distances involved, Black-necked Swans on
the Falkland Islands are considered to be
generally separate from those in continental
South America, but data on the movements of
individual birds is needed to confirm this
assumption.
Current population estimates mean that
South America’s swans do not meet the
Figure 7. Swan distribution in South America: (a) Black-necked Swans and (b) Coscoroba Swans.
(a) Black-necked Swan (b) Coscoroba Swan
62 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
thresholds for classification as “Vulnerable”
in the IUCN Red List for birds (i.e. < 10,000
mature individuals with a continuing decline
of > 30% in ten years or three generations;
BirdLife International 2019a,b), but the lack
of data on population trends means that
this assessment is not secure. The large
ranges for the two species do not approach
the thresholds for Vulnerable under the
range size criteria (i.e. occurrence over
< 20,000 km2, combined with a declining or
fluctuating range size, habitat extent/quality,
or population size with a small number of
locations or severe fragmentation; BirdLife
International 2019a,b), but again better
coordinated monitoring within and across
countries would help to elucidate the situation.
Both the Black-necked Swan and the
Coscoroba Swan are adversely affected by
drought, which can cause loss of breeding
habitat, and are also susceptible to human
development having a detrimental effect
on their food supply. Numbers of Black-
necked Swans at the Carlos Anwandter
Sanctuary in Chile, the most important
breeding area for the species west of the
Andes, plummeted from 4,000–8,000 birds
in 2000–2004 to only a few hundred recorded
annually in 2005–2010 as a result of a
dramatic drop in the abundance of Brazilian
Aquatic Grass Egeria densa (the primary food
for the swans) in the area. The decline was
attributed at the time to the operation of
“Celulosa Arauco” pulp mill, and better
management of liquid waste saw a recovery
in numbers and resumption of breeding on
the wetland from 2012, a total of 6,000–
7,000 adults recorded at the site in December
2016 (Vilina & Flores 2017; Jaramillo et al.
2017). A new and recent threat to Black-
necked Swans in the Carlos Anwandter
Sanctuary is the South American Sea Lion
Otaria flavecens, which has learnt to hunt
swans and has now killed at least 200 birds
at the site (Y. Vilina, pers. comm.).
Overview
On the basis of this review, we estimate that
the total number of swans globally is in
the region of 1.5–1.6 million individuals
(Table 1), but with a further > 110,000
swans (c. 60,000 Mute Swans; 50,000
Black Swans) considered to be non-native
invasive in some areas where they have been
introduced outside their traditional range.
Most of the northern hemisphere swans are
increasing or stable in numbers with
the notable exception of the Northwest
European Bewick’s Swan population, and
information on abundance and/or trends is
lacking for swans wintering in the Caspian
region and Central Asia. Moreover, plans
to change enforcement regulations of the
Migratory Bird Treaty Act in the United
States are also of concern, as potentially
undermining protection for Trumpeter
Swans in North America.
Information on population size and trends
is also rather imprecise for swan species in
Australia and South America (e.g. with trends
estimates for Black-necked Swans dating
back to the 1990s), and there are gaps in
knowledge for a number of populations
in Eurasia, indicating several key regions
where data deficiency should be addressed
(Appendix 1). Whilst undertaking censuses in
large remote areas is challenging, and also of
low priority when species are considered to
be in favourable conservation status and the
work would draw on limited conservation
Conservation status of the world’s swan populations 63
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
resources, nonetheless regular assessments
are important for ensuring that rapid
population changes are not missed. Large-
scale environmental change, for instance in
climate and land-use, means that waterbird
populations including swans may switch
quite promptly from being in favourable
conservation status to going into rapid
decline (as noted for the Northwest
European Bewick’s Swans; Beekman et al.
2019). The situation for swans and other
waterbirds in areas susceptible to drought
and water resource development (e.g. South
America; Australia; Caspian region) therefore
should be monitored, to inform site
protection, habitat management and other
conservation actions required where the
extent and habitat quality at wetlands used by
these species are diminishing or being
degraded. The swans’ large size, which makes
them relatively easy to monitor, should make
them useful indicator species for determining
demographic changes and shifts in
distribution resulting from changes in local or
regional environmental conditions. More
detailed analytical studies are also required, to
determine reasons for declines or changes in
distribution. With most swan populations
currently considered to be increasing (Table
2), studies of the swans’ population ecology
are also required to provide a sound scientific
basis for conflict management, for instance
where agricultural producers are concerned
about potential reductions in crop yields
where goose and swan populations have
increased (Davis et al. 2014).
Acknowledgements
The information presented in this paper is
based on the time and effort spent by swan
counters and researchers from across the
globe who have been actively involved in
counting swans and analysing the resultant
data over many decades, and we are
immensely grateful to all concerned for
providing the evidence that has helped to
substantiate this review. We are grateful
to Kevin Wood for encouraging the
preparation of this paper and to Tony Fox
for providing inspiration through his review
of goose populations which stimulated this
assessment for the swans. We also thank two
anonymous referees and Kevin Wood for
constructive comments on an earlier draft of
the manuscript. PC acknowledges funding
from the Danish Environmental Protection
Agency enabling him to contribute to
sections of the paper on the Northwest
European wintering populations of Bewick’s,
Whooper and Mute Swans.
References
Albertsen, J.O. & Kanazawa, Y. 2002. Numbers
and ecology of swans wintering in Japan.
Waterbirds 25 (Special Publication 1): 74–85.
Arsnoe, D. & Duffiney, A. 2018. From beauty to
beast. Managing Mute Swans in Michigan to
protect native resources. The Wildlife Professional
12: 40–44.
Bakken, V., Runde, O & Tjørve, E. 2003.
Norsk Ringmerkingsatlas. Volym 1.
Lommer-Alkefugler. Ringmerkingscentralen,
Stavaneger, Norway. [In Norwegian with
English summary.]
Barter, M., Lei, G. & Cao, L. 2006. Waterbird
Survey of the Middle and Lower Yangtze River
Floodplain (February 2005). China Forestry
Publishing House, Beijing, China.
Beekman, J., Koffijberg, K., Wahl, J., Kowallik, C.,
Hall, C., Devos, K., Clausen, P., Hornman,
M., Laubek, B., Luigujõe, L., Wieloch, M.,
Boland, H., Švažas, S., Nilsson, L., Stı¯pniece,
64 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
A., Keller, V., Gaudard, C., Shimmings,
P., Larsen, B-H., Portolou, D., Degen, A.,
Langendoen, T., Wood, K.A. & Rees, E.C.
2019. Long-term population trends and
shifts in distribution of Bewick’s Swans
Cygnus columbianus bewickii wintering in
northwest Europe. Wildfowl (Special Issue
No. 5): 73–102.
BirdLife International. 2015. European Red List
of Birds. Available at https://www.birdlife.
org/europe-and-central-asia/news/european-
red-list-birds-here (last accessed 25 August
2019).
BirdLife International (2019a) Species factsheet:
Cygnus melancoryphus. Available at http://www.
birdlife.org (last accessed 11 August 2019).
BirdLife International (2019b) Species factsheet:
Coscoroba coscoroba. Downloaded from http://
www.birdlife.org on 11/08/2019.
Birkhead, M. & Perrins, C.M. 1986. The Mute
Swan. Croom Helm, London, UK.
Blüml, V. & Degen, A. 2009. Höckerschwäne
(Cygnus olor) am Mauserplatz Alfsee
(Niedersachsen): Herkunft, Zusammensetzung
und Bruten. Osnabrücker Naturwissenschaftliche
Mitteilungen 35: 65–76. [In German.]
Blus, L.J., Henny, C.J., Hoffman, D.J., Sileo, L. &
Audet, D.J. 1999. Persistence of high lead
concentrations and associated effects in
Tundra Swans near a mining and smelting
complex in northern Idaho. Ecotoxicology 8:
125–132.
Bønløkke, J., Madsen, J.J., Thorup, K., Pedersen,
K.T., Bjerrum, M. & Rahbek, C. 2006. Dansk
Trækfugleatlas. Rhodos & Zoologisk Museum,
Copenhagen, Denmark. [In Danish with
English summary.]
Brewer, G. & Vilina, Y.A. 2002. Parental care
behavior and double-brooding in Coscoroba
Swan in Central Chile. Waterbirds 25 (Special
Publication 1): 278–284.
Burke, B., Lewis, L.J., Fitzgerald, N., Frost, T.,
Graham Austin, G. & Tierney, T.D. 2018.
Estimates of waterbird numbers wintering in
Ireland, 2011/12 – 2015/16. Irish Birds 11: 1–12.
Callaghan, D., Rees, E. & Harshman, J. 2005.
Swans: taxonomy. In J. Kear (ed.), Bird Families
of the World: Ducks, Geese and Swans, pp. 218–
219. Oxford University Press, Oxford, UK.
Ciaranca, M.A., Allin, C.C. & Jones, G.S. 1997.
Mute Swan (Cygnus olor). In A. Poole (ed.), The
Birds of North America Online. Cornell Lab of
Ornithology, Ithaca, New York, USA.
Cong, P.H., Cao, L., Fox, A.D., Barter, M., Rees,
E.C., Jiang, Y., Ji, W., Zhu, W. & Song,
G. 2011. Changes in Tundra Swan
Cygnus columbianus bewickii distribution and
abundance in the Yangtze River floodplain.
Bird Conservation International 21: 260–265.
Crissey, W.F. 1975. Determination of appropriate
waterfowl hunting regulations. Unpublished
Administrative Report, U.S. Fish and Wildlife
Service, Washington D.C., USA.
Coleman J.T. 2014. Breeding biology of the
Black Swan Cygnus atratus in south-east
Queensland, Australia. Wildfowl 64: 217–230.
Conant, B., Hodges, J.I., Deborah J. Groves, D.J.
& King, J.G. 2002. Census of Trumpeter
Swans on Alaskan nesting habitats, 1968–
2000. Waterbirds 25 (Special Publication 1):
3–7.
Crowe, O., Austin, G.E., Colhoun, K.,
Cranswick, P., Kershaw, M. & Musgrove, A.J.
2008. Estimates and trends of waterbird
numbers wintering in Ireland, 1994/95–
2003/04. Bird Study 55: 66–77.
Davis, J.B., Guillemain, M., Kaminski, R.M.,
Arzel, C., Eadie, J.M & Rees, E.C. 2014.
Habitat and resource use by waterfowl in the
northern hemisphere in autumn and winter.
Wildfowl (Special Issue No. 4): 17–69.
Delany, S., Reyes, C., Hubert, E., Pihl, S., Rees, E.,
Haanstra, L. & van Strien, A. 1999. Results
from the International Waterbird Census in the
Western Palearctic and Southwest Asia 1995 and
1996. Wetlands International Publication No.
Conservation status of the world’s swan populations 65
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
54, Wetlands International, Wageningen, the
Netherlands.
del Hoyo, J., Andrew, E. & Sargatal, J. 1992.
Handbook of the Birds of the World. Volume 1:
Ostrich to Ducks. Lynx Editions, Barcelona,
Spain.
Drewien, R.C., Herbert, J.T., Aldrich, T.W.
& Stephen H. Bouffard. 1999. Detecting
trumpeter swans harvested in tundra swan
hunts. Wildlife Society Bulletin 27: 95–102.
Ely, C.R., Sladen, W.J.L., Wilson, H.M., Savage,
S.E., Sowl, K.M., Henry, B., Schwitters, M. &
Snowdon, J. 2014. Delineation of Tundra
Swan Cygnus c. columbianus populations in
North America: geographic boundaries and
interchange. Wildfowl 64: 132–147.
Esselink, H. & Beekman, J.H. 1991. Between year
variation and causes of mortality in the
non-breeding population of the Mute Swan
Cygnus olor in the Netherlands, with special
reference to hunting. Wildfowl (Special
Supplement No. 1): 110–119.
Fransson, T. & Pettersson, J. 2001. Svensk
ringmärkningsatlas. Volym 1. Lommer-
rovfåglar. Naturhistoriska riksmusset,
Stockholm, Sweden. [In Swedish with English
summary.]
Frost, T., Austin, G., Hearn, R., McAvoy, S.,
Robinson, A., Stroud, D., Woodward, I. &
Wotton, S. 2019. Population estimates of
wintering waterbirds in Great Britain. British
Birds 112: 130–145.
Gaffney, R., 2019. Statewide Waterbird Surveys
1985–2018. Department of Primary Industries,
Parks, Water and Environment (DPIPWE),
Hobart, Tasmania, Australia Available online
at https://dpipwe.tas.gov.au/Documents/
Statewide%20Waterbird%20Surveys.pdf (last
accessed 23 August 2019).
Gale, R.S., Garton, E.O. & Ball, I.J. 1987. The
History, Ecology and Management of the Rocky
Mountain Population of Trumpeter Swans. U.S. Fish
& Wildlife Service, Montana Cooperative
Wildlife Research Unit, Missoula, Montana,
USA.
Garðarsson, A. 1991. Movements of Whooper
Swans Cygnus cygnus neck-banded in Iceland.
Wildfowl (Special Supplement No. 1): 189–194.
Garreaud, R.D., Alvarez-Garreton, C., Barichivich,
J., Boisier, J.P., Christie, D., Galleguillos, M.,
LeQuesne, C., McPhee, J. & Zambrano-
Bigiarini, M. 2017. The 2010–2015
megadrought in central Chile: impacts on
regional hydroclimate and vegetation. Hydrology
and Earth System Sciences 21: 6307–6327.
Gayet, G., Guillemain, M., Rees, E., Wood, K.A.
& Eichholz, M. In press. Mute Swan (Cygnus
olor, Gmelin, 1789). In C.T. Downs & L.A.
Hart (eds.), Global Trends and Impacts of
Alien Invasive Birds. Centre for Agriculture
and Bioscience International (CABI),
Wallingford, UK.
Griffin, L., Rees, E. & Hughes, B. 2011.
Migration routes of Whooper Swans and
geese in relation to wind farm footprints.
WWT Final Report to the Department of
Energy and Climate Change. Wildfowl &
Wetlands Trust, Slimbridge, UK.
Groves, D.J. (comp.) 2017. The 2015 North
American Trumpeter Swan Survey: a Cooperative
North American Survey. U.S. Fish and
Wildlife Service Division of Migratory Bird
Management Juneau, Alaska, USA.
Hall C., Crowe, O., McElwaine, G., Einarsson,
Ó., Calbrade, N. & Rees. E. 2016. Population
size and breeding success of the Icelandic
Whooper Swan Cygnus cygnus: results of the
2015 international census. Wildfowl 66: 75–97.
Handrigan, S.A., Schummer, M.L., Petrie, S.A.
& Norris, D.R. 2016. Range expansion
and migration of Trumpeter Swans Cygnus
buccinator re-introduced in southwest and
central Ontario. Wildfowl 66: 60–74.
Hawkings, J.S., Breault, A., Boyd, S., Orton,
M.N., Beyersbergen, G. & Latour, P. 2002.
Trumpeter Swan Numbers and Distribution
66 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
in Western Canada, 1970–2000. Waterbirds 25
(Special Publication No. 1): 8–21.
Hindman, L.J. & Tjaden, R.L. 2014a. Awareness
and opinions of Maryland citizens toward
Chesapeake Bay Mute Swans Cygnus olor and
management alternatives. Wildfowl 64: 167–185.
Hindman, L.J., Harvey, W.F & Conley, L.E.
2014b. Spraying corn oil on Mute Swan
Cygnus olor eggs to prevent hatching. Wildfowl
64: 186–196.
Hindman, L.J., Harvey, W.F., Walbridge, H.R.,
Hooper, M. & Driscoll, C.P. 2016. An efficient
method of capture and field euthanasia of
flightless Mute Swans. In L.M. Conner &
M.D. Smith (eds.), Proceedings of the 16th
Wildlife Damage Management Conference, pp. 55–
64. Auburn University, Auburn, Alabama,
USA.
Hornman, M., Hustings, F., Koffijberg, K.,
Klaassen, O., van Winden, E., Sovon Ganzen-
en Zwanenwerkgroep & Soldaat, L. 2016.
Watervogels in Nederland in 2014/2015.
Sovon rapport 2016/54, RWS-rapport BM
16.15. Sovon Vogelonderzoek Nijmegen, the
Netherlands. [In Dutch.]
International Union for Conservation of Nature
(IUCN) 2016. Red List of Threatened Species,
Version 2016.1. IUCN, Cambridge, UK.
Available from www.iucnredlist.org (last
accessed 15 August 2017).
Invasive Species Research Team. 2019. Invasive
Species of Japan. Environmental Risk Research
Center, National Institute for Environmental
Studies, Tsukuba, Ibaraki, Japan. Available
online at https://www.nies.go.jp/biodiversity/
invasive/DB/detail/20010e.html (last accessed
1 August 2019).
Lopetegui, E.J., Schlatter Vollman, R., Contreras,
H.C., Valenzuela, C.D. Suarez, N.L., Herbach,
E.P., Huepe, J.U., Jaramillo, G.V., Leischner,
B.P. & Riveros, R.S. 2017. Emigration and
mortality of Black-necked Swans (Cygnus
melancoryphus) and disappearance of the
macrophyte Egeria densa in a Ramsar wetland
site of southern Chile. Ambio 36: 607–610.
Jaramillo, E., Lagos, N.A., Labra, F.A., Paredes,
E., Acuña, E., Daniel Melnick, D., Manzano,
M., Velásquez, C. & Duarte, C. 2018.
Recovery of black-necked swans, macrophytes
and water quality in a Ramsar wetland of
southern Chile: Assessing resilience following
sudden anthropogenic disturbances. Science of
the Total Environment 628/629: 291–301.
Jia, Q., Koyama, K., Choi, C.-Y., Kim, H.-J.,
Cao, L., Gao, D., Liu, G. & Fox A.D.
2016. Population estimates and geographical
distributions of swans and geese in East Asia
based on counts during the non-breeding
season. Bird Conservation International 26: 397–
417.
Kear, J. (ed.). Bird Families of the World: Ducks,
Geese and Swans. Oxford University Press,
Oxford, UK.
Kingsford, R.T. 2000. Ecological impacts of
dams, water diversions and river management
on floodplain wetlands in Australia. Austral
Ecology 25: 109–127.
Kingsford, R.T., Wong, P.S., Braithwaite, L.W. &
Maher, M.T. 1999. Waterbird abundance in
eastern Australia, 1983–92. Wildlife Research
26: 351–366.
Kingsford, R.T., Roshier, D.A. & Porter, J.L.
2010. Australian waterbirds: time and space
travellers in dynamic desert landscapes. Marine
and Freshwater Research 61: 875–884.
Kingsford, R.T., Porter, J.L. & Halse, S.A. 2011,
National Waterbird Assessment. Waterlines
Report Series No. 74. National Water
Commission, Canberra, Australia.
Kingsford, R.T., Bino, G. & Porter, J.L. 2017.
Continental impacts of water development
on waterbirds, contrasting two Australian
river basins: global implications for sustainable
water use. Global Change Biology 2017: 1–12.
Knapik, R.T., Luukkonen, D.R. & Scott R.
Winterstein, S.R. 2019. Density dependence
Conservation status of the world’s swan populations 67
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
in productivity of a North American Mute
Swan Cygnus olor population. Wildfowl (Special
Issue 5): 178–196.
Laubek, B., Knudsen, H.L. & Ohtonen, A. 1998.
Migration and winter range of Whooper
Swans Cygnus cygnus breeding in different
regions of Finland. In B. Laubek (Ph.D.
thesis), The Northwest European Whooper Swan
(Cygnus cygnus) population: ecological and
management aspects of an expanding waterfowl
population, pp. 1–33. University of Aarhus,
Aarhus, Denmark.
Laubek, B., Nilsson, L., Wieloch, M., Koffijberg,
K., Sudfelt, C. & Follestad, A. 1999.
Distribution, numbers and habitat choice of
the NW European Whooper Swan Cygnus
cygnus population: results of an international
census in January 1995. Vogelwelt 120: 141–
154.
Laubek, B., Clausen, P., Nilsson, L., Wahl, J.,
Wieloch, M., Meissner, W., Shimmings, P.,
Larsen, B.H., Hornman, M., Langendoen, T.,
Lehikoinen, A., Luigujõe, L., Stı¯pniece, A.,
Švažas,S., Sniaukstra, L., Keller, V., Gaudard,
C., Devos, K., Musilová, Z., Teufelbauer, N.,
Rees, E.C. & Fox, A.D. 2019. Whooper Swan
Cygnus cygnus January population censuses for
Northwest Mainland Europe, 1995–2015.
Wildfowl (Special Issue 5): 103–122.
Litvin, K. & Vangeluwe, D. 2016. The Bewick’s
Swan is a paradox. Swan News 12: 12.
Ma, M. & Cai, D. 2002. Threats to Whooper
Swans in Xinjiang, China. Waterbirds 25
(Special Issue 1): 331–333.
Matthews, G.V.T. 1972. Conservation. In P. Scott
& the Wildfowl Trust (eds.), The Swans, pp.
182–195. Houghton Mifflin, Boston, USA.
Michigan Department of Natural Resources.
2012. Mute Swan management and control
program policy and procedures. Available
at www.michigan.gov/documents/dnr/
2012_Mute_Swan_Policy_378701_7.pdf (last
accessed 01 March 2016).
Ministry of the Environment. 2018. Japan Integrated
Biodiversity Information System. The Biodiversity
Center, Yamanashi, Japan. Available at http://
www.biodic.go.jp/gankamo/gankamo_top.
html (last accessed 7 August 2019). [In
Japanese.]
Mitchell, C.D. 2018. US Department of the Interior
legal memorandum changes interpretation of
“incidental take” in Migratory Bird Treaty
Act. Swan News 14: 31–33.
Mitchell, C.D. & Eichholz, M.W. 2010.
Trumpeter swan (Cygnus buccinator). In A.
Poole (ed.), The Birds of North America Online.
Cornell Laboratory of Ornithology, Ithaca,
New York, USA.
Miyabayashi, Y. & Mundkur, T. 1999. Atlas of Key
Sites for Anatidae in the Eastern Flyway. Wetlands
International – Japan, Tokyo, Japan and
Wetlands International – Asia Pacific, Kuala
Lumpur, Malaysia.
Moser, T.J. 2006. The 2005 North American
Trumpeter Swan Survey. Division of Migratory
Bird Management, U.S. Fish & Wildlife
Service, Denver, Colorado, USA.
Musgrove, A., Aebischer, N., Eaton, M., Hearn,
R., Newson, S., Noble, D., Parsons, M.,
Risely, K. & Stroud, D. 2013. Population
estimates of birds in Great Britain and
the United Kingdom. British Birds 106: 64–
100.
Musilová, Z., Musil, P., Zouhar, J., Bejc˘ek, V.,
Št’astný, K. & Hudec, K. 2014. Numbers of
wintering waterbirds in the Czech Republic:
long-term and spatial-scale approaches to
assess population size. Bird Study 61: 321–
331.
Newth, J., Colhoun, K., Einarsson, O., Hesketh,
R., McElwaine, G., Thorstensen, S., Petersen,
A., Wells, J. & Rees, E.C. 2007. Winter
distribution of Whooper Swans (Cygnus
cygnus) ringed in four geographically discrete
regions in Iceland between 1988 and 2006: an
update. Wildfowl 57: 98–119.
68 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
Newth, J.L., Brown, M.J. & Rees, E.C. 2011.
Incidence of embedded shotgun pellets in
Bewick’s swans Cygnus columbianus bewickii
and whooper swans Cygnus cygnus wintering in
the UK. Biological Conservation 144: 1630–
1637.
Newth, J.L., Wood, K.A., McDonald, R.A.,
Nuno, A., Semenov, I., Chistyakov, A.,
Mikhaylova, G., Bearhop, S., Belousova,
A., Glazov, P., Cromie, R.L. & Rees,
E.C. 2019. Conservation implications of
misidentification and killing of protected
species. Conservation Science and Practice 1: e24.
Nielsen, R.D., Holm, T.E., Clausen, P.,
Bregnballe, T., Clausen, K.K., Petersen, I.K.,
Sterup, J., Balsby, T.J.S., Pedersen, C.L.,
Mikkelsen, P. & Bladt, J. 2019. Fugle 2012–
2017. NOVANA. Danish Centre for the
Environment and Energy Scientific Report
No. 314. Aarhus University, Rønde, Denmark.
[In Danish.]
Nilsson, L. & Haas, F. 2016. Distribution and
numbers of wintering waterbirds in Sweden
in 2015 and changes during the last fifty
years. Ornis Svecica 26: 3–54.
Olson, S.M. (comp.). 2018. Pacific Flyway Data
Book, 2018. U.S. Department of Interior, Fish
and Wildlife Service, Division of Migratory
Bird Management, Vancouver, Washington
DC, USA.
Pacific Flyway Council. 2001. Pacific Flyway
Management Plan for the Western Population of
Tundra Swans. Pacific Flyway Study Committee,
Subcommittee on Tundra Swans, Unpublished
Report. US Fish & Wildlife Service, Portland,
Oregon, USA.
Parsons, K.C., Mineau, P. & Renfrew, R.B. 2010.
Effects of pesticide use in rice fields on
birds. Waterbirds 33: 193–218.
Petrie, S.A. & Francis, C.M. 2003. Rapid increase
in the lower Great Lakes population of feral
mute swans: a review and a recommendation.
Wildlife Society Bulletin 31: 407–416.
Rawlence, N.J., Kardamaki, A., Easton, L.J.,
Tennyson, A.J.D., Scofield, P.R. & Waters,
J.M. 2017. Ancient DNA and morphometric
analysis reveal extinction and replacement
of New Zealand’s unique black swans.
Proceedings of the Royal Society B 284. DOI:
10.1098/rspb.2017.0876.
Rees, E. 2005. Black-necked Swan Cygnus
melancoryphus. In J. Kear (ed.), Bird Families of
the World: Ducks, Geese and Swans, pp. 227–230.
Oxford University Press, Oxford, UK.
Rees, E.C. & Beekman, J.H. 2010. Northwest
European Bewick’s Swans: a population in
decline. British Birds 103: 640–650.
Rees, E. & Brewer, G.L. 2005. Coscoroba Swan
Coscoroba coscoroba. In J. Kear (ed.), Bird
Families of the World: Ducks, Geese and Swans,
pp. 219–222. Oxford University Press, Oxford,
UK.
Roberts, A. & Padding, P. 2018. Atlantic Flyway
Harvest and Population Survey Data Book. U.S.
Fish and Wildlife Service, Laurel, Maryland,
USA.
Rogers, P.M. & Hammer, D.A. 1998. Ancestral
breeding and wintering ranges of the
Trumpeter Swan (Cygnus buccinator) in the
Eastern United States. Bulletin of the Trumpeter
Swan Society 27: 13–29.
Rose, P.M. & Scott, D.A. 1997. Waterfowl
Population Estimates, 2nd Edition. Wetlands
International Publication No. 44. Wetlands
International, Wageningen, Netherlands.
Rowell, H. & Spray, C. 2004. Mute swan Cygnus
olor (Britain and Ireland population) in Britain
and Northern Ireland 1960–1961–2000–2001.
Waterbird Review Series, The Wildfowl and
Wetlands Trust/Joint Nature Conservation
Committee, Slimbridge, UK.
Rüger, A., Prentice, C. & Owen, M. 1986. Results
of the IWRB International Census 1967–1983.
IWRB Special Publication No. 6. International
Waterfowl and Wetlands Research Bureau
(IWRB), Slimbridge, UK.
Conservation status of the world’s swan populations 69
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
Schlatter, R.P., Navarro, A. & Corti, P. 2002.
Effects of El Niño Southern Oscillation
on numbers of Black-necked Swans at Río
Cruces Sanctuary, Chile. Waterbirds 25 (Special
Issue No. 1): 114–122.
Scott, D.A. 1980. A Preliminary Inventory of
Wetlands of International Importance for Waterfowl
in Western Europe and North-west Africa. IWRB
Special Publication No. 2. International
Waterfowl Research Bureau, Slimbridge,
UK.
Scott, D.A. & Rose, P.M. 1996. Atlas of Anatidae
Populations in Africa and Western Eurasia.
Wetlands International Publication No. 41.
Wetlands International, Wageningen, the
Netherlands.
Scott, P. & the Wildfowl Trust (eds.). 1972. The
Swans. Houghton Mifflin, Boston, USA.
Seabrook-Davison, M. 2013. Mute swan. In
C.M. Miskelly (ed.), New Zealand Birds
Online. Available online at www.nzbirds
online.org.nz (last accessed 1 August 2019).
Sellin, D. 2013. Zum Vorkommen der Schwäne,
Gattung Cygnus im Naturschutzgebiet
Peenemünder Haken, Struck und Ruden.
Ornithologischer Rundbrief für Mecklenburg-
Vorpommern 47: 348–377. [In German.]
Serie, J.R. & Bartonek, J.B. 1991a. Population
status and productivity of Tundra Swans,
Cygnus columbianus, in North America.
Wildfowl (Supplement No. 1): 172–177.
Serie, J.R. & Bartonek, J.B. 1991b. Harvest
management of Tundra Swans Cygnus
columbianus columbianus in North America.
Wildfowl (Supplement No. 1): 359–367.
Serie, J.R., Luszcz, D. & Raftovich, R.V. 2002.
Population trends, productivity, and harvest
of Eastern Population Tundra Swans.
Waterbirds 25 (Special Publication 1): 32–
36.
Shea, R.E., Nelson, H.K., Gillette, L.N., King,
J.G. & Weaver, D.K. 2002. Restoration of
Trumpeter Swans in North America: a
century of progress and challenges. Waterbirds
25 (Special Publication 1): 296–300.
Sheppard, R. 1993. Ireland’s Wetland Wealth: the
Birdlife of the Estuaries, Lakes, Coasts, Rivers,
Bogs and Turloughs of Ireland. The Report of the
Winter Wetlands Survey 1984/85 to 1986/87.
Irish Wildbird Conservancy, Dublin, Ireland.
Silva-García C. & Brewer, G. 2007. Breeding
behavior of the Coscoroba Swan (Coscoroba
coscoroba) in the El Yali wetland, Chile.
Ornitología Neotropical 18: 573–585.
Sladen, W.J.L. 1991. Swans should not be
harvested. Wildfowl (Supplement No. 1):
368–375.
Spray, C.J., Coleman, B. & Coleman, J. 2002. Mute
Swan Cygnus olor. In C.V. Wernham, M.P.
Toms, J.H. Marchant, J.A. Clark, G.M.
Siriwardena & S.R. Baillie (eds.), The Migration
Atlas: Movements of the Birds of Britain and
Ireland, pp. 146–148. T. & A.D. Poyser,
London, UK.
Stafford, J.D., Eichholz, M.W. & Phillips, A.C.
2012. Impacts of Mute Swans (Cygnus
olor) on submerged aquatic vegetation in
Illinois River Valley Backwaters. Wetlands 32:
851–857.
Strebel, N. 2016. Überwinternde Wasservögel in der
Schweiz: Ergebnisse der Wasservogelzählungen
2014/2015 und 2015/2016. Schweizerische
Vogelwarte, Sempach, Switzerland. [In
German.]
Syroechkovski, E.E. 2002. Distribution and
population estimates for swans in the Siberian
arctic in the 1990s. Waterbirds, 25 (Special
Publication 1): 100–113.
Tatu, K.S., Anderson, J.T., Hindman, L.J. &
Seidel, G. 2007. Mute swan’s impact on
submerged aquatic vegetation in Chesapeake
Bay. Journal of Wildlife Management, 71, 1431–
1439.
Teufelbauer, N., Adam, M. & Nemeth, E. 2015.
Analyse der Bestande uberwinternder Wasservogel in
Osterreich 1970–2014. BirdLife Osterreich mit
70 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
Unterstutzung des Bundesministeriums fur
Land- und Forstwirtschaft, Umwelt und
Wasserwirtschaft. Wien, Austria. [In German.]
U.S. Fish and Wildlife Service. 1989. Revised
guidelines for conducting the Midwinter
Waterfowl Survey. Unpublished Report,
Division of Migratory Bird Management,
Laurel, Maryland, USA.
U.S. Fish and Wildlife Service. 2018. Waterfowl
population status, 2018. U.S. Department of
the Interior, Washington D.C. USA.
U.S. Fish and Wildlife Service. 2019. Waterfowl
population status, 2019. U.S. Department of
the Interior, Washington D.C., USA.
Vangeluwe, D., Rozenfeld, S.B., Volkov, S.V.,
Kazantzidis, S., Morosov, V.V., Zamyatin,
D.O. & Kirtaev, G.V. 2018. Migrations of
Bewick’s Swan (Cygnus bewickii): new data
on tagging the migration routes, stopovers,
and wintering sites. Biology Bulletin 45:
90–101.
Vuilleumier, F. 1997. A large autumn
concentration of swans (Cygnus melancoryphus
and Coscoroba Coscoroba) and other Waterbirds
at Puerto Natales, Magallanes, Chilean
Patagonia, and its significance for swan
and waterfowl conservation. Ornitologia
Neotropical 8: 1–5.
Vilina, Y. A. 1994. Apuntes para la conservación
del Humedal del “Estero El Yali”. Boletín
Chileno de Ornitología 1: 15–20.
Vilina, Y.A., Cofré, H., Silva-García, C., García,
M.D. & Pérez-Friedenthal, C. 2002. Effects
of El Niño on abundance and breeding of
Black-necked Swans on El Yali Wetland in
Chile. Waterbirds 25: 123–127.
Vilina, Y.A. & Flores, R. 2017. Population
trends of the Black-necked Swan of Carlos
Anwandter Sanctuary (Rio Cruces) Southern
Chile. Swan News 13: 10–11.
Wang, X., Cao, L., Bysykatova, I., Xu, Z.,
Rozenfeld, S., Jeong, W., Vangeluwe, D.,
Zhao, Y., Xie, T., Yi, K. & Fox, A.D. 2018.
The Far East taiga forest: unrecognized
inhospitable terrain for migrating Arctic-
nesting waterbirds? PeerJ 6: e4353.
Wetlands International. 2019a. Waterbird Population
Estimates. Wetlands International, Ede, the
Netherlands. Accessible at wpe.wetlands.org
(last accessed 1 August 2019).
Wetlands International. 2019b. Waterbird Population
Size and Trend estimates for the 7th Edition of the
Report on the Conservation Status of Migratory
Waterbirds in the AEWA Agreement Area.
Wetlands International, Ede, the Netherlands.
Accessible at http://wpe.wetlands.org/
bundles/voidwalkerswpe/images/CSR7%20
Methodology%20Notes.pdf (last accessed
10 May 2019).
Wetlands International. 2019c. Flyway Trends
Analyses Based on Data from the African-Eurasian
Waterbird Census from the Period of 1967–
2015. Wetlands International, Ede, the
Netherlands. Accessible at http://iwc.
wetlands.org/index.php/aewatrends (last
accessed 10 May 2019).
Williams, M.J. 2013. Black swan. In C.M. Miskelly
(ed.), New Zealand Birds Online. Available
online at www.nzbirdsonline.org.nz (last
accessed 9 August 2019).
Wood, K.A., Newth, J.L., Hilton, G.M. &
Rees, E.C. 2018. Has winter body condition
varied with population size in a long-
distance migrant, the Bewick’s Swan (Cygnus
columbianus bewickii)? European Journal of
Wildlife Research 64: 38. https://doi.org/
10.1007/s10344-018-1200-3.
Wood, K.A., Newth, J.L., Brides, K., Burdekin,
M., Harrison, A.L., Heaven, S., Kitchin, C.,
Marshall, L., Mitchell, C., Ponting, J., Scott,
D.K, Smith, J., Tijsen, W., Hilton, G.M. &
Rees, E.C. 2019a. Are long-term trends in
Bewick’s Swan (Cygnus columbianus bewickii)
numbers driven by changes in winter food
Conservation status of the world’s swan populations 71
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
resources? Bird Conservation International 29:
479–496.
Wood, K.A., Hilton, G.M., Newth, J.L. & Rees,
E.C. 2019b. Seasonal variation in energy gain
explains patterns of resource use by avian
herbivores in an agricultural landscape:
insights from a mechanistic model. Ecological
Modelling 409: 108762.https://doi.org/10.
1016/j.ecolmodel.2019.108762.
Wood, K.A., Brown, M.J., Cromie, R.L., Hilton,
G.M., Mackenzie, C., Newth, J.L., Pain, D.J.,
Perrins, C.M. & Rees, E.C. 2019c. Regulation
of lead fishing weights results in mute swan
population recovery. Biological Conservation
230: 67–74.
Yalden, D. & Albarella, U. 2009. The History
of British Birds. Oxford University Press,
Oxford, UK.
Appendix 1. Monitoring priorities for the world’s swan populations.
Species Population Monitoring priorities
Trumpeter Swan Pacific Coast 5-year censuses; annual age assessments
Rocky Mountain 5-year censuses; annual age assessments
Interior 5-year censuses; annual age assessments; ringing to
monitor & analyse migratory/dispersal patterns for
birds ringed in the reintroduced populations
Tundra Swan Western 5-year censuses; annual age assessments; harvest rates;
monitor incidental take of Trumpeter Swans in
Tundra Swan harvest (e.g. Drewien et al. 1999)
Eastern 5-year censuses; annual age assessments; harvest rates;
monitor incidental take of Trumpeter Swans in
Tundra Swan harvest (e.g. Drewien et al. 1999)
Whooper Swan Icelandic 5-year censuses; annual age assessments; ringing data for
survival estimates and to assess population interchange
NW Mainland 5-year censuses; annual age assessments; ringing data for
Europe survival estimates and to assess population interchange
Black Sea/ Develop censuses & annual age assessments; ringing/
East Med tracking studies for population delineation
Caspian/ Develop censuses & annual age assessments;
W Siberian ringing/tracking studies for population delineation
East Asian Develop censuses & annual age assessments;
ringing/tracking studies for population delineation
Bewick’s Swan NW European 5-year censuses; annual age assessments; ringing for
survival estimates and to determine level of
population interchange with Caspian population
72 Conservation status of the world’s swan populations
©Wildfowl & Wetlands Trust Wildfowl (2019) Special Issue 5: 35–72
Appendix 1 (continued).
Species Population Monitoring priorities
Bewick’s Swan (cont.) Caspian Develop surveys to determine population size and
trends; annual age assessments; ringing/tracking for
survival estimates and to determine level of
population interchange with NW European population
Eastern Coordinate international surveys to determine total
population size and trends; annual age assessments;
tracking to describe subpopulations
Mute Swan Ireland Censuses to update population size estimates at 10-year
intervals
Britain Censuses to update population size estimates at 10-year
intervals
NW Mainland & Censuses to update population size and distribution
Central Europe estimates at 10-year intervals
Black Sea Develop censuses to determine population size, trends
and distribution
West & Central Develop censuses to determine population size, trends
Asia/Caspian and distribution
Central Asia Develop censuses to determine population size, trends
and distribution
East Asia Develop censuses to determine population size, trends
and distribution
Black Swan Australia Census population size & develop trend estimates at
10-year intervals
Black-necked Swan South America Develop coordinated counts to determine population
size & trends; develop ringing programme to
understand movements & survival rates
Falkland Islands Develop coordinated counts to determine population
size & trends; develop ringing programme to
understand movements & survival rates
Coscoroba Swan South America Develop coordinated counts to determine population
size & trends; develop ringing programme to
understand movements & survival rates
... The observed decline in Bewick's Swan numbers was in contrast to many other populations of large herbivorous waterbirds in Europe, which have shown stable or increasing population trends since the Bewick's Swan population peaked in the mid-1990s (Rees et al. 2019). These include two congeners of the Bewick's Swan that are also native to Europe: the Mute Swan (Cygnus olor), which is largely sedentary throughout northwest Europe, and the two populations of migratory Whooper Swan (Cygnus cygnus), one of which breeds in Iceland and winters in the UK and Ireland, while the other breeds in northwest Russia and Fennoscandia, and winters in mainland northwest Europe (Rees et al. 2019). ...
... The observed decline in Bewick's Swan numbers was in contrast to many other populations of large herbivorous waterbirds in Europe, which have shown stable or increasing population trends since the Bewick's Swan population peaked in the mid-1990s (Rees et al. 2019). These include two congeners of the Bewick's Swan that are also native to Europe: the Mute Swan (Cygnus olor), which is largely sedentary throughout northwest Europe, and the two populations of migratory Whooper Swan (Cygnus cygnus), one of which breeds in Iceland and winters in the UK and Ireland, while the other breeds in northwest Russia and Fennoscandia, and winters in mainland northwest Europe (Rees et al. 2019). Mute Swan numbers across Europe have shown regional variation, but in almost all regions have either increased or have remained stable since the mid-1990s (Rees et al. 2019;Wood et al. 2019a). ...
... These include two congeners of the Bewick's Swan that are also native to Europe: the Mute Swan (Cygnus olor), which is largely sedentary throughout northwest Europe, and the two populations of migratory Whooper Swan (Cygnus cygnus), one of which breeds in Iceland and winters in the UK and Ireland, while the other breeds in northwest Russia and Fennoscandia, and winters in mainland northwest Europe (Rees et al. 2019). Mute Swan numbers across Europe have shown regional variation, but in almost all regions have either increased or have remained stable since the mid-1990s (Rees et al. 2019;Wood et al. 2019a). Whooper Swan numbers have more than doubled since 1995 (Hall et al. 2016;Laubek et al. 2019). ...
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Abstract Background Winter numbers of the northwest European population of Bewick’s Swans (Cygnus columbianus bewickii) declined recently by c. 40%. During the same period, numbers of two sympatric and ecologically-similar congeners, the Mute Swan (Cygnus olor) and Whooper Swan (Cygnus cygnus) showed increases or stability. It has been suggested that these opposing population trends could have a causal relationship, as Mute and Whooper Swans are larger and competitively dominant to Bewick’s Swans in foraging situations. If so, effects of competition of Mute and Whooper Swans on Bewick’s Swans should be detectable as measurable impacts on behaviour and energetics. Methods Here, we studied the diurnal behaviour and energetics of 1083 focal adults and first-winter juveniles (“cygnets”) of the three swan species on their winter grounds in eastern England. We analysed video recordings to derive time-activity budgets and these, together with estimates of energy gain and expenditure, were analysed to determine whether individual Bewick’s Swans altered the time spent on key behaviours when sharing feeding habitat with other swan species, and any consequences for their energy expenditure and net energy gain. Results All three swan species spent a small proportion of their total time (0.011) on aggressive interactions, and these were predominantly intraspecific (≥ 0.714). Mixed-effects models indicated that sharing feeding habitat with higher densities of Mute and Whooper Swans increased the likelihood of engaging in aggression for cygnet Bewick’s Swans, but not for adults. Higher levels of interspecific competition decreased the time spent by Bewick’s Swan cygnets on foraging, whilst adults showed the opposite pattern. When among low densities of conspecifics (
... 200-300 birds (up to 367 in 2017) resident in Japan (Rees et al. 2019;Carboneras & Kirwan 2020;Gayet et al. 2020). The distribution, migration routes and behaviours were largely unknown or undocumented, except for scattered sites used as wintering, breeding and stopover areas, although Inner Mongolia was known to be an established summering area and a stopover site for this population (Zhao et al. 2008). ...
... The Mute Swan Cygnus olor is the most abundant of the swan species, with a total of seven populations distributed around the world, in total comprising > 600,000 individuals (Rees et al. 2019;Wetlands International 2019). It is also the beststudied of all of the swans, with more research undertaken than on any of the other true swans Cygnus sp. ...
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Until recently, almost nothing was known about the migration routes, flyway structure and population status of the Mute Swan Cygnus olor in East Asia. Here, we use a combination of GPS telemetry data, collar resightings, published literature and expert advice to update existing knowledge of its summer and winter distribution in the region, and to provide a preliminary description of the swans’ migration and habitat use. Three flyway units were indicated for the Mute Swan in East Asia. The Eastern China-wintering unit includes swans summering along the lower Selenga River in Russia, in central Mongolia and Inner Mongolia in China, which winter on the coast of eastern China, where 403 swans were recorded in 2014/15 but where fewer than 30 have been counted in very recent years. In the absence of better data, we conservatively estimate this Chinese-wintering group at 400 birds. Mute Swans in the Korean-wintering unit are individuals that winter along the Korean Peninsula and summer in Inner Mongolia (China) and the Amur region (on the border of China and Russia); they are poorly covered by the mid-winter waterbird counts in South Korea and we have no knowledge of numbers wintering in North Korea. Finally, mid-winter counts of the introduced and sedentary population of Mute Swans in Japan have amounted to c. 240 birds in the last five years. We therefore suspect that there are likely c. 1,000 Mute Swans in Far East Asia, but await improved coverage throughout the entire wintering grounds to provide a better population estimate, with the species confirmed as one of the poorer known of the migratory waterbirds in the region. A single GPS-tagged Mute Swan tracked successfully provided detailed information on its migration routes, timing of migration and habitat use (almost exclusively waterbodies) over four complete migration episodes. It summered at Dalai Lake, China, used three stopover sites (on the borders of Russia and North Korea, in North Korea, and Baicheng City in China) during spring and autumn migration, and showed site fidelity to summer, winter and stopover sites. Combined count data and GPS data suggested that Mute Swans mostly occur within protected areas throughout the year. However, further research is required to establish the true distribution and abundance of this small and scattered species within these three flyways in East Asia, as well as to confirm its population structure and migration routes.
... Since bottlenecks frequently occur that affect the genetic diversity of wildlife, including at the MHC, the question then arises: what was the level of diversity of class I MHC in the reservoir population of wild swans? This is not known; in addition, the size of swan populations in Western and Central Asia is considered by conservationists to be uncertain (Rees et al., 2019). ...
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Every year commercial poultry operations produce and crowd billions of birds, a source of inexpensive animal protein. Commercial poultry is intensely bred for desirable production traits, and currently presents very low variability at the Major Histocompatibility Complex. This situation dampens the advantages conferred by the MHC’s high genetic variability, and crowding generates immunosuppressive stress. We address the proteins of influenza A viruses directly and indirectly involved in host specificities. We discuss how mutants with increased virulence and/or altered host specificity may arise if few class I alleles are the sole selective pressure on avian viruses circulating in immunocompromised poultry. This hypothesis is testable with peptidomics of MHC ligands. Breeding strategies for commercial poultry can easily and inexpensively include high variability of MHC as a trait of interest, to help avoid the billions of dollars in disease burden caused by influenza and decrease the risk of selecting highly virulent strains.
... The Whooper Swan Cygnus cygnus breeds across the northern Palearctic, from Iceland and northern Scandinavia to the Pacific coast of Russia, with five flyway populations described on the basis of their geographical separation in the breeding or wintering ranges (Rees 2005; Wetlands International 2020; Rees et al. 2019). Those breeding and wintering in Europe have been assigned to the two westernmost populations -the Icelandic and the Northwest Mainland European (hereafter NWME) populations. ...
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The eighth international census of Whooper Swans Cygnus cygnus wintering in Britain, Ireland and Iceland (also including the Isle of Man and the Channel Islands) took place in January 2020, to update the estimates of the size, midwinter distribution, habitat use and breeding success of the Icelandic Whooper Swan population. The total of 43,255 swans counted represented a 27.2% increase in numbers since the previous census in 2015. Overall, 36.8% of the population (15,927 birds) was recorded in England, 33.4% (14,467) in the Republic of Ireland, 11.7% (5,052) in Scotland, 10.7% (4,644) in Northern Ireland and 6.8% (2,923) in Iceland, with < 1% (242) in Wales, the Isle of Man and the Channel Islands combined. Despite numbers increasing in both the Republic of Ireland and Northern Ireland since 2015, the proportion of the total population in the Republic of Ireland was significantly lower in 2020 and no significant difference was detected for Northern Ireland, whereas proportions in England and Scotland were significantly higher in 2020 and lower in Iceland. Breeding success was not associated with temperatures on either the breeding or wintering grounds. It also showed no clear trend over time, suggesting that increased survival may be the demographic driver of the population growth.
... Changes in the management and productivity of farmland in the last few decades have elicited modified ways of utilizing foraging habitat in most agricultural areas (Atkinson et al. 2005). The destruction of natural wetlands and the population growth of some waterfowl have led to the increased use of crop fields by these birds (Owen 1990;MacMillan et al. 2004;Leito et al. 2008;Hake et al. 2010;Radtke & Dieter 2011;Rosin et al. 2012;Rees et al. 2019). Dense, single-species crops such as early-growth cereals in agricultural landscapes offer elevated energetic and nutritional intake rates of higher-quality food that is attractive to feeding birds, leading in effect to conflicts with farmers (Bischof et al. 2012;Eythórsson et al. 2017;. ...
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Changes in the management and productivity of farmland affect foraging behaviour in migrating birds. Crops are increasingly being damaged (and farmers are sustaining ever greater economic losses) as a result of large flocks of waterfowl feeding on them. To investigate the differences in the time budget shared between natural grasslands and arable lands, migrating Greater White-fronted Geese (Anser albifrons) were filmed using digiscoping equipment at a spring stopover site. Four types of activity were noted in connection with habitat types, bird age, position in the flock and flock size. Foraging was the most common activity in both habitats, but was more common in the grasslands than on arable land. The mean times spent on vigilance, resting and other activities were also significantly different between the two habitat types. GLM analysis showed that young birds spent more time foraging than adults but revealed no differences in foraging times between the age categories in grasslands and arable land. In the latter, geese were more vigilant at the edge of a flock and rested more frequently in its centre. No such differences were found in the grasslands. Only resting time was adversely affected by flock size. These findings, which demonstrate that White-fronted Geese are flexible in their use of food resources, could be useful in agricultural management planning in the light of increasing conflicts with farmers.
... suggested a minimum population size of 41,842 birds. The Japanese-wintering population trend has been reported as stable in recent years (Ministry of the Environment 2019; Rees et al. 2019), following an increase during the second half of the 20th century (Albertsen & Kanazawa 2002), and their migration routes from Japan have been documented by satellite telemetry (Shimada et al. 2014). Little is known about the numbers and trends of Whooper Swans wintering in China, and the breeding origins and migration routes of Chinese-wintering Whooper Swans are poorly understood, although some stopover sites used by Whooper Swans have been identified (Zhang et al. 2016;Li et al. 2018;Jia et al. 2019). ...
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The migration routes and migratory patterns of Whooper Swans Cygnus cygnus summering in western Mongolia have not previously been described and the status of East Asian population is currently uncertain. Here we therefore use a combination of satellite tracking data, sightings of colour-marked individuals, published literature and expert knowledge to determine their distribution and site-use more precisely. Results indicated that the swans’ summer distribution extended further than had previously been recorded, with three new wintering areas (in Xinjiang, Qinghai Gansu and Beijing) identified for the species in China. The East Asian Whooper Swan population was estimated to number 57,690 individuals, generating a new 1% threshold of 577 birds for determining sites of international importance for the species in the region. Using count data from winters 2011/12–2018/19, we identified eight wintering sites of international importance for the species in China, six in South Korea and 14 in Japan. Annual variation in national count totals highlighted the need to improve survey effort in China. Individual swans showed considerable within-winter fidelity to their wintering sites, with limited exchange between wintering areas. Migration duration, stopover duration, the number of stopover sites and migration legs were significantly greater in spring than in autumn, whilst migration speed was slower in spring than in autumn. Assessment of the habitats frequented found seasonal variation in the proportion of time that the swans spent on arable crops, pasture, wetlands and open water. From their GPS locations, 46.9%, 25.5%, 35.3% and 0.0% of the tagged swans were in protected areas during the summer, autumn staging, winter and spring staging periods, respectively. Our results provide a basis for the conservation of Whooper Swans in East Asia and illustrate the need for improved monitoring and further research into their migration, particularly for informing the protection and management of the main stopover and wintering sites for the species in China.
... 146 million Anatidae of 56 species (over 1 million swans, 39 million geese and some 95 million freshwater duck species; Rees et al. 2019;Fox & Leafloor 2018;Wetlands International 2020). These huge numbers of waterbirds exploit the surge of summer biological productivity to reproduce there, but fly elsewhere to survive the winter (Dalby et al. 2014). ...
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Long-distance migratory waterbirds contribute many ecosystem functions and services, not least as important huntable quarry species, as well as posing challenges to human societies, through agricultural crop damage, threats to flight safety and pathogen transmission. As a result, throughout much of the Northern Hemisphere, they have received considerable research attention to identify discrete population flyways upon which to build monitoring programmes, a basis for their effective internationally coordinated conservation management, especially in North America and Europe. However, until recently, we lacked comparable information about migratory Anatidae populations in Far East Asia, despite long-term monitoring programmes and some knowledge of migration routes based on Japanese satellite tracking. In this article, we set the scene for the presentation of the species accounts for 10 large-bodied Anatidae species, which follow in this Special Issue of Wildfowl, and which attempt to fill some of the gaps in knowledge about these important species in Far East Asia. Papers in the Special Issue combine new telemetry data, winter counts and expert knowledge on the 10 species, to update maps of the extent of breeding and wintering areas, and to define the flyways that connect them. Critical stopover sites and the remotely-sensed habitats that these waterbird populations exploit along the way are also described, to provide a basis for their more effective future conservation.
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Two of the most fundamental ecological questions about any species relate to where they occur and in what abundance. Here, we combine GPS telemetry data, survey data and expert knowledge for the first time to define two distinct flyways (the East Asian Continental and West Pacific flyways), migration routes and abundance for the Eastern population of Bewick’s Swan Cygnus columbianus bewickii. The Eastern population is the largest flyway population, supporting c. 77% of Bewick’s Swan numbers globally. GPS telemetry data showed that birds breeding in the Russian arctic from the Yamal Peninsula to c. 140°E (including the Lena and Yana Deltas), winter in the middle and lower reaches of the Yangtze River in China (which we label the “East Asian Continental flyway”). Bewick’s Swans breeding from the Indigirka River east to the Koluchin Bay winter in Japan, mostly in Niigata, Yamagata and Ishikawa Prefectures (the “West Pacific flyway”). There was no overlap in migration routes used by tagged individuals from the two flyways. Counts of Bewick’s Swans in the East Asian Continental flyway during the 21st century have shown wide between-year variations, reflecting incomplete coverage in earlier years. Bewick’s Swans in this flyway currently numbers c. 65,000 birds based on extensive wintering survey coverage, compared to c. 81,000 in the early 2000s, based on less complete coverage. Chinese-wintering swans now concentrate mainly (c. 80%) at Poyang Lake in Jiangxi Province and Hubei Lakes (mostly in Longgan Lake), compared to a more widespread distribution both within Poyang and throughout the Auhui Lakes in 2004 and 2005. In contrast, Bewick’s Swans of the West Pacific flyway now numbers c. 40,000, compared to just 542 in 1970. This population has shown no significant overall change since 2004, when it numbered c. 45,000 birds. Small numbers within this population probably also winter in South Korea. These results provide our first basic understanding of the winter distribution of Chinese- and Japanese-wintering Bewick’s Swans in relation to their breeding areas, confirming the need to coordinate future research and monitoring in the two flyways, as well as the need for more information on swans wintering in South Korea.
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The results of the November 2018 census clearly reflected the drought in the summer and autumn of 2018. Total numbers were average, but the populations of some dabbling duck species were well above the average of recent years. Further, Mute Swan Cygnus olor, Goosander Mergus merganser, Grey Heron Ardea cinerea and Great White Egret Egretta alba, Ferruginous Duck Aythya nyroca and several species of geese showed new all-time highs in wintering numbers. For most species, these highs result from long-term positive trends. In some areas, January census was hampered by bad weather conditions. The total count in January 2019 was below the average of the last years. The low total number mainly results from long-term declines of some abundant species. Declining total numbers were found on the majority of waterbodies, with the most significant ones on Lake Geneva, lower part of Lake Constance and Lake Lucerne. However, numbers have also declined on rivers and reservoirs. The most significant increases were found at Lake Neuchâtel and in the Rhine delta area at Lake Constance. Climate change is supposed to be the main driver for the found shifts. Counts on Lake Geneva used to be particularly high in cold winters. Winters in which the shores and shallow water zones of Lake Neuchâtel freeze over are becoming rarer. As a result, Lake Geneva is used less, while the numbers on Lake Neuchâtel are rising. At regional level, the distribution of increases and decreases also indicates that waterbirds are increasingly concentrated in areas where they are well protected from disturbance. Formerly important areas with inadequate or missing protec- tion would provide food for waterbirds, but the increasing and more and more year-round activities on lakes seem to make it increasingly difficult for them to use these areas.
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Coordinated international censuses of the Northwest European Bewick’s Swan Cygnus columbianus bewickii population have been undertaken across the swans’ wintering range at c. 5-year intervals since 1984. During the early years of the study, numbers increased steadily to a peak of 29,780 individuals in January 1995, but then declined by 39.4% to 18,057 swans counted in January 2010 before showing a partial recovery to 20,149 recorded in January 2015. Changes in distribution across the wintering range were also recorded; a higher proportion of the population now remains in more easterly countries (notably Germany) in mid-winter, whilst only a handful of birds migrated to Ireland (at the western edge of the range) during the 2000s compared to >1,000 wintering there at the start of the study. Variation between censuses in the proportion of swans recorded in different parts of the range were attributable to weather conditions, with more swans wintering further north in warmer years. The overall percentage of cygnets recorded in each of the census years ranged from 9.6% in 2010 to 13.2% in 2005, with no obvious consistency over time in the distribution of cygnets across the wintering range. There were however changes between 1990 and 2015 in the swans’ use of feeding habitats, with a decline in the proportion of birds on pasture and a corresponding increase in those on arable land. Decreases in the total population size and changes in distribution in the 21st century have implications for the designation and resultant protection of sites of international importance for the species.
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Annual monitoring of wintering waterbirds is carried out under the I-WeBS and WeBS schemes in the Republic and Northern Ireland respectively. These surveys are carried out from September to March each year, largely by a dedicated volunteer network, and are the principal tools used in the conservation of Ireland’s wintering waterbirds and their wetland habitats. This study presents population estimates and 1% thresholds for wintering waterbirds in Ireland for the period 2011/12 to 2015/16 inclusive. Estimates were generated based on annual peak counts with imputation and include the results of more targeted surveys (i.e. goose and swan species censuses, non-estuarine surveys) where these improve the accuracy of estimates for the species in question. Estimates were generated for a total of 44 waterbird species, using data from 684 wetland sites across the Republic of Ireland and Northern Ireland. The total number of waterbirds estimated was 757,910, comprising 38% wildfowl (21 species), 6% wildfowl allies (8 species) and 57% waders (15 species). Total numbers have declined by 138,160 (15%) since the 2006/07-2010/11 period, with waders experiencing the largest declines; the combined totals of 15 wader species having declined by over 19%. Golden Plover Pluvialis apricaria and Lapwing Vanellus vanellus were the most numerous wader species recorded and Wigeon Mareca penelope and Teal Anas crecca were the most numerous wildfowl. Eight of the 44 species have increased by more than 5% since the previous estimates for 2006/07 – 2010/11, whereas 29 species declined by 5% over the same period. Many species are undergoing similar declines at flyway level, although the impact of local pressures and threats at Irish wetland sites should not be overlooked. Ireland continues to hold internationally important numbers of several waterbird populations, most notably Icelandic Whooper Swan Cygnus cygnus, Greenland White-fronted Goose Anser albifrons flavirostris, Greenland Barnacle Goose Branta leucopsis, East Canadian High- Arctic Light-bellied Brent Goose Branta bernicla hrota, Europe-wintering Great Northern Diver Gavia immer, North European Ringed Plover Charadrius hiaticula, Icelandic Black-tailed Godwit Limosa limosa islandica and North European/North Russian Bar-tailed Godwit Limosa lapponica.
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Our understanding of how energy shapes animal behavioural decisions has been limited by the difficulty of measuring directly the energy gain and expenditure in free-living animals. Mechanistic models that simulate energy gain and expenditure from estimable parameters can overcome these limitations and hence could help scientists to gain a predictive understanding of animal behaviour. Such models could be used to test mechanistic explanations of observed patterns of resource use within a landscape, such as behavioural decisions to switch among food resources. Here, we developed mechanistic models of the instantaneous and daily rates of net energy gain for two species of migratory swans, the Bewick's swan (Cygnus columbianus bewickii) and whooper swan (Cygnus cygnus), that feed on root and cereal crops within an agricultural landscape in eastern England. Field data show that both species shift from using predominantly root crops (e.g. sugar beet and potatoes) in early winter to using mostly cereals (e.g. wheat) in late winter. Our models correspondingly predicted that swans could achieve the greatest rates of net energy gain on root crops in early winter and on cereal crops in late winter. The change from root crops to cereal crops providing the greatest net rates of energy gain was predicted to occur at the same time as the birds' switch from feeding predominantly on root crops to predominantly cereal crops (between December and January). We used Monte Carlo simulations to account for variance in model parameters on predictions of energy gain and profitability. A sensitivity analysis indicated that predictions of net energy gain were most sensitive to variance in the intake rate and food quantity parameters. The agreement between our model estimates of energy gain and the observed shifts in resource use observed among the overwintering swans suggests that maximising net rates of energy gain is an important resource selection strategy among overwintering birds. A mechanistic understanding of where and when birds will use food resources can inform the conservation management of key feeding areas for species of conservation concern, as well as the deployment of crop protection strategies.
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The migration corridors of Bewick's swan, which inhabits the Yamalo-Nenets Autonomous District , were identified in 2015-2017 using GPS-GMS transmitters. It was shown that even the individuals that inhabit the same region widely used different wintering sites. The birds that nest and molt in southern Yamal (Baydaratskaya Bay) were found to migrate through two corridors: the eastern corridor that leads to southeastern China and the western one that leads to the Caspian Sea, the Evros River delta, countries of Central and Middle Asia, and northwestern China. Fourteen key stopover sites were revealed. We explain the appearance of new Asian and European wintering sites by the general increase in the species' numbers and believe that the decrease in the size of the Northern European population that has been observed since the mid-1990s is due to a loss of natural habitats. We have shown for the first time that the wintering range of Bewick's swan with the revealed Asian wintering sites being taken into account is quite large. As the climate changes, some stopover sites can be used as wintering sites, which may lead to an even greater expansion of the wintering range of the species in the future.
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This 381-paged book covers the biology, ecology, impact and management of 34 common alien invasive species, with reviews on the history and context of avian introductions and invasions in five major regions (Oceania, Africa, Europe (including the Middle East, Asia and South America)), as well as management challenges and the potential of citizen science for monitoring alien birds. The book pitches at the introductory level and is ideal for readers to gain a quick and comprehensive view of the current status of global avian invasions. It has brought the records and research of avian invasion one step ahead of other alien invasive animal taxa. Many chapters contain distribution maps and data tables on the diet and morphology of the species, providing a good reference for the species and its management issues. Each chapter also contains a rich list of references that could help readers dive further into the topic.
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The north-west European population of Bewick’s Swan Cygnus columbianus bewickii declined by 38% between 1995 and 2010 and is listed as ‘Endangered’ on the European Red List of birds. Here, we combined information on food resources within the landscape with long-term data on swan numbers, habitat use, behaviour and two complementary measures of body condition, to examine whether changes in food type and availability have influenced the Bewick’s Swan’s use of their main wintering site in the UK, the Ouse Washes and surrounding fens. Maximum number of Bewick’s Swans rose from 620 in winter 1958/59 to a high of 7,491 in winter 2004/05, before falling to 1,073 birds in winter 2013/14. Between winters 1958/59 and 2014/15 the Ouse Washes supported between 0.5 and 37.9 % of the total population wintering in north-west Europe (mean ± 95 % CI = 18.1 ± 2.4 %). Swans fed on agricultural crops, shifting from post-harvest remains of root crops (e.g. sugar beet and potatoes) in November and December to winter-sown cereals (e.g. wheat) in January and February. Inter-annual variation in the area cultivated for these crops did not result in changes in the peak numbers of swans occurring on the Ouse Washes. Behavioural and body condition data indicated that food supplies on the Ouse Washes and surrounding fens remain adequate to allow the birds to gain and maintain good body condition throughout winter with no increase in foraging effort. Our findings suggest that the recent decline in numbers of Bewick’s Swans at this internationally important site was not linked to inadequate food resources.