# Recent changes in the abundance of breeding Common Pochard Aythya ferina in Europe

Anthony David Fox, Alain Caizergues, Mikhail Banik, K. Devos, M. Dvorak, M. Ellermaa, Benjamin Folliot, Andy J. Green, C. Grünenberg, Mathieu Guillemain, et al.

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Anthony David Fox, Alain Caizergues, Mikhail Banik, K. Devos, M. Dvorak, et al. Recent changes in the abundance of breeding Common Pochard Aythya ferina in Europe. Wildfowl, 2016, 66, pp.22-44. hal-04699609

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# Recent changes in the abundance of Common Pochard *Aythya ferina* breeding in Europe

A.D. FOX¹*, A. CAIZERGUES², M.V. BANIK³, K. DEVOS⁴, M. DVORAK⁵,
M. ELLERMAA⁶, B. FOLLIOT⁷,⁸, A.J. GREEN⁹, C. GRÜNEBERG¹⁰,
M. GUILLEMAIN⁷, A. HÄLAND¹¹, M. HORNMAN¹², V. KELLER¹³,

A.I. KOSHELEV¹⁴, V.A. KOSTIUSHYN¹⁵, A. KOZULIN¹⁶, Ł. ŁAWICKI¹⁷,
L. LUIGUJÕE¹⁸, C. MÜLLER¹³, P. MUSIL¹⁹, Z. MUSILOVÁ¹⁹,
L. NILSSON²⁰, A. MISCHENKO²¹, H. PÖYSÄ²², M. ŠČIBAN²³,
J. SJENIČIĆ²⁴, A. STĪPNIECE²⁵, S. ŠVAŽAS²⁶ & J. WAHL¹⁰

¹Department of Bioscience, Aarhus University, Kalø, Grenåvej 14, DK-8410 Rønde, Denmark.

²Office National de la Chasse et de la Faune Sauvage, Unité Avifaune Migratrice, Parc d'Affaires La Rivière, 8 Boulevard Albert Einstein, Bâtiment B, CS F-42355-44323 Nantes, France.

³Research Institute of Biology, V.N. Karazin Kharkiv National University, Svobody Square 4, Kharkiv, 61022 Ukraine.

⁴Research Institute for Nature and Forest, Kliniekstraat 25, 1070 Brussels, Belgium.

⁵BirdLife Österreich, Museumsplatz 1/10/8, A-1070 Vienna, Austria.

⁶Taivaanvuohentie 3 A 2, FIN-00200 Helsinki, Finland.

⁷Office National de la Chasse et de la Faune Sauvage, Unité Avifaune Migratrice, La Tour du Valat, Le Sambuc, F-13200 Arles, France.

⁸Institut de Recherche de la Tour du Valat, Le Sambuc, F-13200 Arles, France.

⁹Estación Biológica de Doñana EBD-CSIC, c/ Americo Vespucio s/n, 41092 Sevilla, Spain.

¹⁰Dachverband Deutscher Avifaunisten e.V., Federation of German Avifaunnists, An den Speichern 6, Münster D-48157, Germany.

¹¹Norwegian Nature Information, Paradisleitet 14, NO-52311 Paradis, Bergen, Norway.

¹²SOVON, Dutch Centre for Field Ornithology, PO Box 6521, 6503 GA Nijmegen, Netherlands.

¹³Swiss Ornithological Institute, Seerose 1, CH-6204 Sempach, Switzerland.

¹⁴Bohdan Khmelnytsky Melitopol State Pedagogical University, Lenin Street 20, Melitopol, Zaporizhzhya Region, 72312 Ukraine.

¹⁵I.I. Schmalhausen Institute of Zoology, vul. B. Khmelnytskogo 15, Kyiv, 01030 Ukraine.

¹⁶Scientific Center of the Biological Resources of National Academy of Science of Belarus, Academicheskaya str. 27, 220072 Minsk, Belarus.

¹⁷West-Pomeranian Nature Society, Pionierów 1/1, PL-74-100 Gryfino, Poland.

¹⁸Estonian University of Life Sciences, Institute of Agricultural and Environmental Sciences, Kreutzwaldi 5, EE-51014 Tartu, Estonia.
**Abstract**

National accounts suggest that the Common Pochard *Aythya ferina* was an uncommon breeding bird throughout western Europe before 1850. Extensions to the breeding range in the late 19th century were potentially aided by the rapid development of managed fish-ponds in eastern Europe, which provided suitable novel habitat at that time. Expansion into western Europe followed in subsequent decades. Wetland and waterbody eutrophication throughout Europe, which likely provided food and cover for the birds, may have accelerated the rapid expansion from the 1950s until the early 1980s. Widespread declines in the last 30 years, especially in eastern Europe, where breeding numbers are highest, are possibly linked to intensification and/or abandonment of freshwater fish farming and changes in water quality. Studies show that Pochard gain fitness benefits from nesting in Black-headed Gull *Chroicocephalus ridibundus* colonies and hence has been affected by major losses of European gull colonies in the last 30 years. The spread of alien fish species such as the Carp *Cyprinus carpio*, which compete with Pochard for food resources, is a problem in the Mediterranean region. Changing predation pressures (in some cases linked to invasive alien mammals) are also implicated in some areas. Relatively modest numbers breeding in the UK, France and the Netherlands have remained stable or increased over the same recent span of years, confirming that different factors currently affect Pochard breeding abundance throughout its range. We urgently need better information relating to key factors affecting Pochard breeding success and abundance, which is currently showing an unfavourable conservation status throughout much of Europe.

**Key words:** *Aythya ferina*, breeding, Common Pochard, population declines, population stressors.

<footnote n="19">¹⁹Department of Ecology, Faculty of Environmental Sciences, Czech University of Life Sciences, Kamycka 1176, CZ-165 21, Prague 6, Czech Republic.</footnote>

<footnote n="20">²⁰Department of Biology, University of Lund, Ecology Building, Lund, S-223 62, Sweden.</footnote>

<footnote n="21">²¹Severtsov's Institute of Ecology and Evolution, Leninsky Avenue 33, Moscow 119071, Russia.</footnote>

<footnote n="22">²²Natural Resources Institute Finland, Yliopistokatu 6, FI-80100 Joensuu, Finland.</footnote>

<footnote n="23">²³Bird Protection and Study Society of Serbia, Vladika Ćirića 24, RS-21000 Novi Sad, Serbia.</footnote>

<footnote n="24">²⁴Society for Research and Protection of Biodiversity, Brace Potkonjaka 16, BA-78 000 Banja Luka, Bosnia and Herzegovina.</footnote>

<footnote n="25">²⁵Institute of Biology, University of Latvia, Miera Street 3, LV-2169 Salaspils, Latvia.</footnote>

<footnote n="26">²⁶Laboratory of Avian Ecology, Lithuanian Nature Research Centre, Akademijos Str. 2, LT-08412 Vilnius, Lithuania.</footnote>

<footnote>*Correspondence author. E-mail: tfo@bios.au.dk</footnote>
The Common Pochard (hereafter Pochard)
*Aythya ferina* is a numerous and widespread
diving duck, which breeds largely in
freshwater to the south of the tundra
region across the Palearctic from Iceland to
the steppe lakes of Mongolia and the
Daurian region (Kear 2005). It winters
throughout Europe, in northern Africa
along the Nile as far as Sudan, the
Mediterranean, Black and Caspian Sea
regions, and the Indian sub-continent,
through to southern China, Korea and
Japan (Kear 2005; Reeber 2015). Latest
estimates put the global population at
between 1.95 and 2.45 million individuals
(Wetlands International 2016), which
suggests it is as numerous as its ecological
counterparts in North America combined
(the Redhead *Aythya americana* at 1.35
million and the Canvasback *A. valisineria*
with 0.69 million; Wetlands International
2016). Since the 1850s, the Pochard has
expanded its breeding range north and
westwards, colonising Fennoscandia,
Scandinavia, Britain and the Netherlands,
and since the 1950s has spread into
Mediterranean countries including Greece,
Italy, Spain and North Africa (Bezzel 1969;
Hagemeijer & Blair 1997). For much of the
last 150 years the species therefore appears
to have expanded and consolidated its
breeding range within Europe.

More recently, however, the assessment
for the European Red List of Birds 2015
(BirdLife International 2015a), indicated
that there were serious reductions in the
distribution and abundance of breeding
Pochard from the late 20th century onwards,
resulting in the European population being
upgraded from IUCN Least Concern status

to Vulnerable on the basis of a 30–49%
decline in breeding population size over the
course of three generation spans (22.8 years;
after BirdLife International 2015a). This
reflects similar declines in numbers recorded
on its wintering grounds, which after a long
period of relative stability have decreased
by 50%, to c. 150,000 birds in northern
Europe between the late 1980s–2012, and
to c. 600,000 in Central Europe, the
Mediterranean and Black Sea region slightly
later during the late 1990s–2012 (Nagy et al.
2014). The species therefore is now also
designated as being globally Vulnerable
(IUCN 2015).

How could a species that has consistently
shown expansion of its breeding distribution
and increases in winter abundance in,
for instance the United Kingdom from
the 1940s until the 1990s (Eltringham
& Atkinson-Willes 1961; Holt et al.
2011), suddenly be in such unfavourable
conservation status? Clearly, overall
population size in relatively long-lived duck
species can be affected by changes in
survival rate, but in the case of the Eurasian
Wigeon *Anas penelope* it has recently been
shown that changes in annual reproductive
output may also have a major impact on
flyway population size (Fox et al. 2016). It is
difficult to relate changes in Pochard
abundance in specific breeding areas
with changes in winter numbers and
distribution because many of the birds
wintering in Europe may originate from
central Eurasia (e.g. Fox & Salmon 1988;
Keller et al. 2009; A. Caizergues et al.
in press). Nonetheless, in this review
we have attempted to assess the relative
abundance of the Pochard population
breeding in European countries now and
in the recent past, to determine the existing
distribution of breeding birds across range
states, to compare the colonisation history
for Pochard in these countries and to
assess recent population trends for different
parts of the range. We also sought to
compile published assessments of the
factors considered responsible for the
differing trends in breeding abundance, in
an attempt to understand the underlying
causes for the variation in trends, and to
provide recommendations for sympathetic
management of breeding habitat, to restore
the former breeding abundance of Pochard
wherever possible.

## Methods

Following a workshop convened at the Pan-
European Duck Symposium in Hanko in
Finland on 9 April 2015, national experts
were approached and asked to compile
information on Pochard from national
count databases and reports, for as many
European countries as possible, in order
to develop a profile of the past breeding
status, current breeding status and an
estimated trend in the abundance of
breeding pairs over the last 10–12 years
for short-term trends and since the 1980s
for longer term trends. Although we
attempted to assess changes in annual
breeding success and survival, these were
rarely available because the Pochard
is generally neither a well-studied nor
effectively monitored species, except at the
classic study sites at Lake Engure in Latvia
(e.g. Nichols et al. 1997; Opermanis et al.
2001) and Lac de Grand-Lieu in France
(e.g. Gourlay-Larour et al. 2014). We were

especially interested to learn about any
information relating to factors that might
have specifically affected female survival
and reproductive output (e.g. predation
pressure), as well as any changes in habitat
quality that might influence the food
supply, nesting cover and its overall
attractiveness to the species for breeding.
This resulted in the expression of much
opinion, but relatively few studies were
available to relate such changes directly to
reductions in nesting abundance and/or
breeding success.

## Results

Contrasting recent national trends
in breeding Pochard abundance
throughout Europe

Country-specific data and interpretation
of trends can be found in the detailed
country accounts which are available in
Supporting Materials (http://wildfowl.wwt.
org.uk/index.php/wildfowl/rt/suppFiles/
2638/0).

The full list of national population
estimates and recent trends for those
countries thought to support <1% of the
total European breeding population are
shown in Table 1, while Table 2 shows
the data for the 15 countries thought to
support ≥ 1% of Pochard breeding in
Europe (data from BirdLife International
2015b, modified in accordance with the
results of the review presented here).
Trends in national breeding abundance over
the last 20–30 years are shown in Fig. 1,
where it is evident that, amongst the
countries supporting > 100 breeding pairs,
48% of 29 counties showed declines,
<table><caption>**Table 1.** Reported national European breeding population sizes of Pochard for countries supporting <1,500 breeding pairs (i.e. <1% of the total European breeding population). Data from BirdLife International (2015b), with modifications by the authors. Percentage change is not indicated for countries with <100 breeding pairs.</caption><thead><tr><th rowspan="2">Country</th><th colspan="3">Current population estimate</th><th colspan="3">Short term population trend</th><th colspan="3">Long term population trend</th></tr><tr><th>Pairs</th><th>% Europe</th><th>Period</th><th>Quality</th><th>% Change</th><th>Period</th><th>Quality</th><th>% Change</th><th>Period</th><th>Quality</th></tr></thead><tbody><tr><td>Luxembourg</td><td>1</td><td>&lt;1</td><td>2008–2012</td><td>good</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Albania</td><td>0–5</td><td>&lt;1</td><td>2002–2012</td><td>good</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Kosovo</td><td>&lt;10</td><td>&lt;1</td><td>2009–2014</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Montenegro</td><td>&lt;10</td><td>&lt;1</td><td>2002–2012</td><td>poor</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Switzerland</td><td>&lt;11</td><td>&lt;1</td><td>2008–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Norway</td><td>&lt;15</td><td>&lt;1</td><td>2000–2013</td><td>good</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>FYRO Macedonia</td><td>&lt;20</td><td>&lt;1</td><td>2001–2012</td><td>poor</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Georgia</td><td>Present</td><td>&lt;1</td><td>?</td><td>?</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Portugal</td><td>&lt;50</td><td>&lt;1</td><td>2008–2012</td><td>poor</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Greece</td><td>30–80</td><td>&lt;1</td><td>2008–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Slovenia</td><td>50–100</td><td>&lt;1</td><td>2007–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Moldova</td><td>100–120</td><td>&lt;1</td><td>2000–2010</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Austria</td><td>130–200</td><td>&lt;1</td><td>2001–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Bosnia HG</td><td>100–200</td><td>&lt;1</td><td>2010–2014</td><td>poor</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Italy</td><td>150–200</td><td>&lt;1</td><td>2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Bulgaria</td><td>80–250</td><td>&lt;1</td><td>2005–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Denmark</td><td>280</td><td>&lt;1</td><td>2011</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Armenia</td><td>100–350</td><td>&lt;1</td><td>2002–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Slovakia</td><td>300–500</td><td>&lt;1</td><td>2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>United Kingdom</td><td>350–630</td><td>&lt;1</td><td>2006–2010</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Belgium</td><td>500–1,000</td><td>&lt;1</td><td>2008–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Estonia</td><td>500–1,000</td><td>&lt;1</td><td>2008–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Turkey</td><td>500–1,000</td><td>&lt;1</td><td>2013</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Serbia</td><td>870–1,250</td><td>&lt;1</td><td>2008–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Sweden</td><td>700–1,500</td><td>&lt;1</td><td>2008–2012</td><td>medium</td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table><table><tbody><tr><td></td><td>-30 to -40</td><td>2000–2010</td><td>medium</td><td>-20 to -40</td><td>0</td><td>1980–2010</td><td>medium</td><td></td><td></td><td></td></tr><tr><td></td><td>0</td><td>2001–2012</td><td>medium</td><td>0</td><td></td><td>1980–2012</td><td>poor</td><td></td><td></td><td></td></tr><tr><td></td><td>?</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td>-50</td><td>2000–2012</td><td>medium</td><td>-25 to -40</td><td>+5 to +20</td><td>1980–2012</td><td>medium</td><td></td><td></td><td></td></tr><tr><td></td><td>fluctuating</td><td>2000–2012</td><td>good</td><td>-50 to -100</td><td></td><td>1980–2012</td><td>good</td><td></td><td></td><td></td></tr><tr><td></td><td>-20 to -33</td><td>1999–2011</td><td>good</td><td></td><td></td><td>1980–2011</td><td>good</td><td></td><td></td><td></td></tr><tr><td></td><td>?</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td>-30 to -50</td><td>2000–2012</td><td>medium</td><td>+10 to +25</td><td>+216</td><td>1980–2012</td><td>medium</td><td></td><td></td><td></td></tr><tr><td></td><td>+36</td><td>1996–2008</td><td>good</td><td>+178 to +567</td><td></td><td>1971–2008</td><td>good</td><td></td><td></td><td></td></tr><tr><td></td><td>0</td><td>2000–2012</td><td>poor</td><td>+20 to +50</td><td></td><td>1973–2012</td><td>poor</td><td></td><td></td><td></td></tr><tr><td></td><td>-20 to -50</td><td>2001–2012</td><td>medium</td><td>0</td><td></td><td>1980–2012</td><td>medium</td><td></td><td></td><td></td></tr><tr><td></td><td>-70 to -89</td><td>2000–2012</td><td>good</td><td></td><td></td><td>1990–2013</td><td>poor</td><td></td><td></td><td></td></tr><tr><td></td><td>+1 to +9</td><td>2000–2012</td><td>medium</td><td>0</td><td></td><td>1980–2012</td><td>medium</td><td></td><td></td><td></td></tr><tr><td></td><td>0</td><td>2001–2012</td><td>medium</td><td>-35 to -91</td><td></td><td>1980–2012</td><td>medium</td><td></td><td></td><td></td></tr></tbody></table>
<table><caption>**Table 2.** Reported national European breeding population sizes of Pochard for countries supporting ≥1,500 breeding pairs (i.e. ≥ 1% of the total European breeding population). Data from BirdLife International (2015b), with modifications by the authors.</caption><thead><tr><th rowspan="2">Country</th><th colspan="3">Current population estimate</th><th colspan="3">Short-term population trend</th><th colspan="3">Long-term population trend</th></tr><tr><th>Pairs</th><th>% Europe</th><th>Period</th><th>Quality</th><th>% Change</th><th>Period</th><th>Quality</th><th>% Change</th><th>Period</th><th>Quality</th></tr></thead><tbody><tr><td>Latvia</td><td>1,500-2,000</td><td>1</td><td>2004</td><td>medium</td><td>?</td><td></td><td></td><td>-20 to -50</td><td>1994-2004</td><td>medium</td></tr><tr><td>Netherlands</td><td>1,307-2,621</td><td>1</td><td>2008-2011</td><td>medium</td><td>0</td><td>2002-2011</td><td>good</td><td>0</td><td>1984-2011</td><td>good</td></tr><tr><td>Hungary</td><td>2,000-3,000</td><td>1</td><td>2000-2012</td><td>poor</td><td>-60 to -70</td><td>2000-2012</td><td>poor</td><td>-60 to -70</td><td>1980-2012</td><td>poor</td></tr><tr><td>Lithuania</td><td>2,000-2,500</td><td>1</td><td>2008-2012</td><td>medium</td><td>-30 to -40</td><td>2001-2012</td><td>medium</td><td>-30 to -40</td><td>1980-2012</td><td>medium</td></tr><tr><td>Belarus</td><td>3,000-4,000</td><td>1</td><td>2009-2010</td><td>medium</td><td>-50</td><td>2001-2012</td><td>medium</td><td>-50</td><td>1980-2012</td><td>medium</td></tr><tr><td>Croatia</td><td>1,000-5,000</td><td>1</td><td>2013</td><td>poor</td><td>?</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>France</td><td>3,000-5,000</td><td>2</td><td>2009-2012</td><td>medium</td><td>?</td><td></td><td></td><td>-20 to -40</td><td>1985-2012</td><td>poor</td></tr><tr><td>Germany</td><td>4,000-5,500</td><td>2</td><td>2005-2009</td><td>good</td><td>-31 to -100</td><td>1998-2009</td><td>medium</td><td>-21 to -50</td><td>1985-2009</td><td>medium</td></tr><tr><td>Poland</td><td>2,000-11,000</td><td>3</td><td>2008-2012</td><td>medium</td><td>?</td><td></td><td></td><td>-20 to -100</td><td>1980-2012</td><td>good</td></tr><tr><td>Ukraine</td><td>7,000-12,000</td><td>4</td><td>2015</td><td>medium</td><td>declining</td><td>2010-2015</td><td>medium</td><td>declining</td><td>1980-2012</td><td>medium</td></tr><tr><td>Spain</td><td>8,300</td><td>4</td><td>2007</td><td>medium</td><td>fluctuating</td><td>1998-2009</td><td>medium</td><td>fluctuating</td><td>1980-2009</td><td>medium</td></tr><tr><td>Finland</td><td>10,000-16,000</td><td>5</td><td>2006-2012</td><td>good</td><td>-69 to -82</td><td>2001-2012</td><td>good</td><td>-51 to -67</td><td>1986-2012</td><td>good</td></tr><tr><td>Czech Rep</td><td>9,000-17,000</td><td>5</td><td>2001-2003</td><td>medium</td><td>+90 to +110</td><td>2001-2013</td><td>good</td><td>-40 to -50</td><td>1981-2013</td><td>good</td></tr><tr><td>Romania</td><td>20,698-28,762</td><td>10</td><td>2008-2013</td><td>medium</td><td>?</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Russia</td><td>90,000-120,000</td><td>44</td><td>2008-2011</td><td>poor</td><td>-1 to 10</td><td>2000-2010</td><td>poor</td><td></td><td></td><td></td></tr></tbody></table>
<figure><img src="image_3.png" /><figcaption>**Figure 1.** Map showing the relative abundance of breeding Pochard *Aythya ferina* in each European country, as indicated by relative arrow/bar size. Abundance is measured in terms of the maximum number of breeding pairs recorded in the last 20–30 years (see Tables 1 and 2 for details). Countries supporting <100 breeding pairs in this period are omitted. Arrows indicate countries with increasing (upward) and declining trends (downward), bars indicate no trends.</figcaption></figure>

including European Russia, Czech Republic, Poland and Finland, which currently constitute the four most important states numerically for breeding Pochard. Only five (17%) countries (Belgium, Bulgaria, Estonia, Slovakia and United Kingdom) showed long-term increases. Since all of

these countries supported < 1,000 breeding pairs, they contributed relatively little to the overall totals. There were no discernible geographical trends, suggesting that contrasting trends reflect different pressures on breeding abundance in different countries.
## Longer term trends in breeding abundance and causes of change

In attempting to synthesise the “colonisation” by breeding Pochard throughout Europe, it was extremely difficult to determine precisely when the species first bred in each country. It was quite impossible to determine whether Pochard recorded as breeding “for the first time” had merely returned after a period of extirpation, had genuinely reproduced in a previously unoccupied country, or indeed had been present and undetected for many years. Hence, while many countries cite a specific year for the first “recorded” case of proven breeding, it is rarely possible to determine if this did indeed represent the year in which the country was first colonised. There were some glaring anomalies; for instance, while it was clear that European Russia, Ukraine and the Baltic States had all hosted breeding Pochard from before the mid 1800s, Belarus (which is totally surrounded by these states) first recorded breeding in 1926. What does seem evident is that Pochard were recorded as first breeding in Finland, Sweden and Denmark during the period 1849–1867 (see Supporting Materials), so this does seem to represent a northwestern extension of range during the second half of the 19th century. Pochard are also thought to have reached Iceland and the United Kingdom at around the same time. Numbers in these countries do not seem to have consolidated until much later in the 20th century, however, and Norway did not experience its first breeding record until 1972. Nevertheless, it seems likely from the combined accounts that there was also a major extension of the

range west into Germany (where the species was more confined to the east in former years), the Netherlands and the UK in the late 1880s, which was consolidated by Pochard colonising Belgium in the first half of the 20th century, a period during which there was apparent expansion and increasing breeding abundance in France and Spain. What does seem reasonably consistent was the more evident increase in breeding abundance across much of the range that seemed to simultaneously occur from the 1950s until the mid to late 1980s (see Supporting Materials). This period of increase and expansion of the breeding population of Europe was also characterised by increases in the wintering population in Western Europe (Atkinson-Willes 1967; Fox & Salmon 1988; Nagy et al. 2014).

## Potential causes of changes in breeding abundance

In hindsight, we cannot understand the factors affecting the expansion of range and the increase in breeding numbers that occurred within Europe starting in the early 1800s, but more recent increases in nesting range and abundance in the 1950s–1980s were linked in several countries to the creation of artificial waterbodies (e.g. reservoirs constructed for drinking water, flood relief or hydro-electric power, or the flooding of mineral extraction sites such as sand and gravel quarries), especially in areas with nutrient-rich waters (see the summary of reported factors contributing to Pochard breeding increases in Table 3). This may reflect a successful niche shift or merely opportunism on the part of species whose
former rarity merely reflected the scarcity of
its habitat. Either way, the expansion in the
area and number of suitable open
waterbodies through the creation and
management of artificial fish-ponds for
aquaculture also had a major effect,
especially in eastern Europe, where such
management created optimal conditions
with high levels of fertilisation and regular
water table drawn down (Table 3). As it
expanded its breeding range westwards, the
species seemingly took advantage of long-
established extensive areas of fish-ponds, as
in France for example, which had been
previously unoccupied. In more recent
times, both the reduction in intensity
and abandonment of such aquaculture
practices on the one hand, and increasing
intensification of fish management on the
other (in the sense that more feed, nutrients
and medication treatments are being applied
to the same bodies of water), have been
shown to affect breeding Pochard in France
(Broyer *et al.* in press) and cited as the causes
of declines in breeding Pochard in Austria,
Czech Republic, Hungary, Poland and
Ukraine, as well as potentially elsewhere.
Changes in water chemistry (especially due
to hyper-eutrophication of waterbodies
caused by agricultural runoff) are also cited
in several countries as potentially being
responsible for declining Pochard breeding
numbers, as are the knock-on effects of
these on reductions in benthos biomass,
excessive growth of emergent macrophytes
and loss of submerged macrophytes (Table
3). Direct competition between Common
Carp *Cyprinus carpio* and adult and duckling
Pochard was found in some studies (Pykal &
Janda 1994; Musil *et al.* 1997; Musil 2006).

Increased predation rates are often cited as a
cause of declines in Pochard nesting
abundance, particularly those involving
introduced alien species, such as Raccoons
*Procyon lotor*, Raccoon Dogs *Nyctereutes
procyonoides* and American Mink *Mustela vison*,
but predation by Red Fox *Vulpes vulpes* and
other native predators (including Wild Boar
*Sus scrofa*) were also cited.

Some of these effects may involve
complex interactions with other species,
such as the Black-headed Gull *Chroicocephalus
ridibundus* with which nesting Pochard
frequently associate. Pochard breeding in
association with gull colonies apparently
benefit from elevated breeding success and
female survival in comparison with
occasions where they do not do so (e.g.
Väänänen 2000; Väänänen *et al.* 2016). Since
the Black-headed Gull is declining across
much of the Pochard's breeding range,
authors from several countries proposed
that this trend has contributed to the local
decline of Pochard in their region. Despite
the association between gull colonies and
Pochard breeding success, however, we
cannot reject the alternative explanation that
a common factor is involved in the decline
of both Black-headed Gull and Pochard
where they co-occur. Abandonment of
grazing of wetland vegetation on the one
hand and excessive cutting of wetland
vegetation and loss of reedbeds on the other
have also been implicated in the loss of
suitable nesting cover, together with falling
water levels and habitat destruction and
degradation (Table 3).

Table 3 indicates that some universal
factors may be behind the decline of
Pochard across Europe, specifically
hyper-eutrophication of waters, loss of gull colonies and predation by American Mink. It is clear, however, that both the abandonment and conversely the intensification of fish-farm management (which is largely restricted in practice to eastern European countries) have also been cited as major causes of change in Pochard nesting numbers in the very parts of the range where the species was formerly most common, and is now showing the greatest declines.

# Discussion

## Differences in trends between countries

The results of this survey support the hypothesis that the Pochard breeding population has recently experienced significant declines across many countries. Amongst the countries supporting 100–1,000 pairs, the long-term trends are mixed. Most are stable or increasing, with the notable exceptions of Moldova, Italy, Denmark and Sweden, but in the shorter term, many more countries show declines, including Turkey in the south of the breeding range (Table 1).

In contrast, the majority of the short and long-term trends for the countries supporting > 1,000 breeding pairs of Pochard are showing consistent declines (Table 2), several of major magnitude, which gives considerable cause for concern given the disproportionate contributions (> 90%) these states make to the European breeding population. The numbers of Pochard breeding in European Russia, for example, are considered to have declined by up to 10% during 2000–2010 alone and the upper

estimate of population size has fallen by 50% (although there remains considerable imprecision about the estimates compared to those in smaller countries further west). Furthermore, we know relatively little about how the breeding numbers further east in Russia (i.e. outside of Europe and beyond the scope of this review) have fared in the same period, because many of the breeding birds from these areas also contribute to European wintering numbers, which have fallen dramatically in recent years (Nagy et al. 2014). Hence, whilst trends in breeding abundance in some of the countries with relatively low numbers in the west of the range and those which have been recently colonised seem to be reasonably favourable, those in areas with greatest numbers and especially those in the north and east of the range seem to be experiencing the greatest rates of decline. Despite evidence of recent increases in Mediterranean areas, longer term prospects are poor given climate change, increased water abstraction and invasive species, which will lead to loss of habitat, increased salinity and hypertrophy in remaining wetlands (Moss et al. 2009).

## Management options to address declines throughout the European breeding range

Although it is important to stress that for many of the factors we lack hard evidence for the ultimate causes of the decline in European breeding Pochard, the congruence of factors reported from many different countries supports the hypothesis that there may be some common causes (see Table 3). Regionally, macro-environment
conditions (such as poor weather during
laying and incubation or drought) could
contribute a common cause to explain
regional declines. Pochard do seem to select
to nest on eutrophic (and in many cases
ephemeral) wetlands (Kear 2005), which
makes them susceptible to nutrient and
hydrological change given the relative rarity
and unstable nature of such wetland types.
Several authors noted the benefit of the
provision of new waterbodies in the form
or reservoirs, gravel pits and fish-ponds as
habitat for breeding Pochard, which likely
fuelled the expansion of its range and
population size during the middle part of
the last century. The eutrophication of such
waters as a result of the increasing use of
inorganic fertilisers in agriculture from the
1950s onwards was also cited as providing
enhancement of suitable breeding habitat
for Pochard during their period of range
extension and consolidation. Continuation
of nutrient enrichment however typically
elevates primary production, leading to
overgrowth of reed-beds and willow scrub
at cost to open water in such wetlands.
Increased phytoplankton and water turbidity
in remaining open water also restricts
benthos and submerged macrophyte
communities (Ekholm & Mitikka 2006) and
ultimately the attractiveness to breeding
duck species, including Pochard (Lehikoinen
et al. 2016). The European Water
Framework Directive (WFD) adopted in
2000 aims to restore good ecological status
to all surface waters by 2027, including the
mediation of such eutrophication effects,
although there is wide agreement that such a
timescale for delivery is overly optimistic
(e.g. Hering et al. 2010). Hence, to restore

breeding Pochard populations at sites of
particular significance to the species in the
short term (especially in protected areas
where water quality issues are associated
with catchment processes outside the
jurisdiction of the protected area), specific
site-based remedial action plans are required
to tackle problems associated with local
water quality. There also remain considerable
challenges associated with remediation
and reinstatement of hyper-eutrophicated
waters (e.g. Jarvie et al. 2013), so recreating
suitable conditions for Pochard and other
breeding waterbirds may present longer term
conservation management targets in such
situations. Meanwhile, successful wetland
restoration projects at some key breeding
sites for Pochard, as, for example, recently
implemented in the Baltic States, have
resulted in immediate increases in numbers
of breeding as well as staging Pochard
(Viksne et al. 2010), which gives hope that
targeted wetland creation and restoration can
contribute to local increases in nesting
abundance.

Drought, especially in the south and
southeast of Europe, has reduced the
reliability of ephemeral wetlands appearing
during spring and summer, to which
breeding Pochard are attracted. Although
management of hydrological abstraction
from rivers and waterbodies can moderate
such effects, in the face of changing patterns
of precipitation and increasing temperatures
associated with climate change, there is little
beyond enhancing water management that
can be done to safeguard important
breeding sites for Pochard under such
circumstances. Climate change acts in
tandem with water abstraction, resulting in
salinity increases at wetlands, rendering them unsuitable for Pochard (Jeppesen et al. 2015).

Changes in management of fish-ponds, either as a result of intensification (which results in the negative effects reported for eutrophication, or direct feeding competition between Carp and Pochard adults and young), or abandonment has reduced the potential carrying capacity of this very important anthropogenic habitat to support breeding Pochard (e.g. Broyer et al. in press). Although we lack firm scientific confirmation that expert opinion has identified the key drivers of changes in Pochard abundance correctly, it does seem that changes in east European aquaculture have played a disproportionate role in the decline in numbers of Pochard breeding in that part of the range. Nevertheless, the future appropriate management of these sites does provide some options for restoring nesting Pochard populations. For instance, agri-environmental and food security support mechanisms may be available to support sustainable and ecologically friendly aquaculture production in rural areas otherwise suffering poor employment opportunities.

Predation on nests and incubating females must also have an effect on the reproductive potential of the Pochard population to reproduce successfully, even where nesting conditions are perfect, and many countries reported adverse changes in predation levels due to several, often interacting processes. In France, the Wild Boar constitutes a problem and with increases in their abundance and distribution could become a source of

greater predation pressure in the future (e.g. Elmberg et al. 2009). However, most evident in some other states were the presence of non-native predator species, such as Raccoon Dog, Raccoon and American Mink, all of which are able to access nests on islands, in reed-beds and on floating vegetation. However, while the evidence for the magnitude of the specific impacts of these three predator species on nesting duck species remains equivocal (e.g. Nordström et al. 2003; Kauhala 2004; Nordström & Korpimäki 2004; Väänänen et al. 2007: Kauhala & Kowalczyk 2011), there is good evidence for the ecological impacts of American Mink and potential to prevent and mitigate the effects of this species (e.g. Bonesi & Palazon 2007). A rich literature from North America shows that local predator control in areas of high duck nesting densities increases nesting success (e.g. the pioneering work of Duebbert & Lokemoen 1980), but the intervention tends to be financially costly, requires consistent sustained investment over much larger areas than a single duck breeding site and is not likely to have effects at the population level (Côté & Sutherland 1997). Other exotic species that may have potential influence on breeding Pochard in France include the Coypu *Myocastor coypus*, Muskrat *Ondatra zibethicus*, Red Swamp Crayfish *Procambarus clarkii* and Catfish *Silurus* sp. as well as some non-native exotic plants (e.g. Water Primrose *Ludwigia* sp.) which are all thought to exert an adverse effect on natural vegetation (A. Caizergues, unpubl. data). Bonesi & Palazon (2007) stressed the requirement for strategic solutions and in particular for sensitising public and government agencies
to the need to respond nationally and internationally to invasive alien species. As of January 2015, the EU has implemented a new Regulation on Invasive Alien Species 2015 (European Commission 2014) with the major objective (under the EU's Biodiversity Strategy Target 5 for 2020) to coordinate EU-wide actions to prevent, minimise and mitigate the adverse impacts of invasive alien species (IAS) on biodiversity and ecosystem services, the economy and public health. The Regulation seeks to establish three types of measures, namely: (i) prevention, (ii) early warning and rapid response and (iii) management of already established IAS. Within EU member states, therefore, there is now a vital imperative on statutory bodies to manage IAS (including through international coordination), which provides a much needed imperative to tackle some of the species considered here to be a challenge to the effective maintenance of breeding Pochard numbers.

Although Black-headed Gull colonies did not improve Pochard reproductive success significantly at Grand-Lieu in France (B. Folliot, unpubl. data), loss of gull colonies elsewhere (which provide protection from predators of eggs and hatchlings as a result of the gulls' communal mobbing behaviour, and have been shown to elevate Pochard reproductive success and female survival; Väänänen 2000; Blums et al. 2003) is frequently cited as being the cause of lost or reduced breeding Pochard numbers. Although the Black-headed Gull population is declining across much of Europe, local declines have been ascribed to different causes, e.g. in Latvia to a reduction in fishing-related activities and mink farms,

where gulls could feed (Viksne 1997) and in Denmark to reduction in food availability at mink farms, changes in stock grazing intensity on grassland and the switch from spring-sown to autumn-sown cereals (Bregnballe et al. 2015). For such reasons associated with large-scale land use and changes in husbandry and aquaculture, there is little short-term likelihood of restoring food sources for nesting gull colonies. However, where changes in grazing pressure and cutting or loss of reed-beds are concerned, local management to restore such features and enhance the attraction of local wetland nesting habitat are clearly high priorities for the feasible sympathetic management for breeding Pochard.

Finally, it should not be forgotten that Pochard are huntable in several east European states from 1 August, which selects for breeding females and naive juveniles prior to their departure to winter quarters. This, together with drowning in fishing nets at the same stage in the annual cycle, also represents a source of avoidable mortality that could be mitigated that may otherwise increasingly contribute to local population decline.

Overall, therefore, it would seem that the expansion in the range and size of the Pochard population breeding in Europe was supported in the middle of the last century by habitat creation and nutrient enrichment, which was not possible to sustain in contemporary landscapes. Continued eutrophication of some waters and loss of other wetlands (especially amongst fishponds that seem to have supported particularly high numbers) has contributed to the subsequent decline over the last 2–3
decades, potentially exacerbated by elevated
predation rates from a suite of predatory
species that include some invasive alien
species. There seems little doubt that local
sympathetic site management can mitigate
some of these impacts where there is good
evidence for the local cause of declines
in breeding abundance, but given the
magnitude of the problem and the likely
diversity of local factors involved, it would
seem that in the short term at least, we need
to accept that the breeding population of
Pochard in Europe in the coming few
decades will be lower than in the recent past.
In this respect, it is clear that appropriate
management is needed to stabilise the
current population trend, while research and
monitoring is concurrently implemented to
understand the critical causes behind the
declines and better track population change.
There is a clear incentive to ensure that
those sites that currently contribute the
most important breeding concentrations of
this declining species are effectively
protected and subject to optimal
management to maintain and enhance
numbers of breeding Pochard present.
However, we must also face the reality that
this is a species that breeds in small numbers
on large numbers of waterbodies and
restoration of the quality of those waters
remains a priority if we are to restore
breeding numbers to former levels of
abundance. In this respect, the Pochard
presents us with a series of new nature
conservation challenges, being a red-listed
species which remains relatively common
and widespread, but nevertheless with a
relatively narrow ecological niche. As a
result, it may not attract attention from

conservation NGOs and agencies in the
first instance, yet it could decline to
relatively low population levels relatively
quickly without clear management
prescriptions for its rescue. Moreover, the
Pochard may be experiencing additional
negative demographic changes, which lay
outside of the scope of this review, such as
enhanced mortality outside of the breeding
season (e.g. through changes in hunting
mortality, drowning in fishing nets and
suffering lead poisoning from lead shot
in the environment), which may be
contributing to current rapid declines in its
overall abundance.

The species therefore deserves an
integrated flyway-wide approach to its
population management, taking into
account of all the interacting processes
which limit and regulate its abundance,
preferably under an internationally agreed
flyway management plan. Such an approach
is vital for understanding the effects on
population size of the factors discussed
above in relation to the breeding season,
relative to those that operate at other critical
points through the remainder of the annual
cycle (e.g. staging, moulting, wintering, etc.).
Such knowledge is vital to balance and
prioritise cost-effective conservation actions
to restore the species to more favourable
conservation status. In this respect, it may
be a useful case study for other wetland
species in similar situations, where it is clear
that we require improved systems for the
collection of key baseline data (e.g. objective
measurement of annual national nesting
abundance and breeding female survival
in all countries, and of local factors that
may be affecting these measures), in order
to support evidence-based conservation management actions needed to maintain and ultimately restore local breeding abundance to previously higher levels. It is important that such coordinated research and monitoring be instigated across its range before the species approaches levels that are considered critically rare.

## Acknowledgements

We are extraordinarily grateful to the enormous numbers of observers who have contributed to our knowledge of breeding Pochard over the generations, without which this account could not have been compiled. Thanks to Eileen Rees, Blas Molina, Richard Hearn and an anonymous referee for their suggestions for improvements to an earlier version of this manuscript.

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**Photograph:** Common Pochard male, with female in the background, at Jeziorsko, Poland, by Adam Mańka.