recent changes in the abundance of common pochard … et al... · 22 ©wildfowl & wetlands...

22

© Wildfowl & Wetlands Trust Wildfowl (2016) 66: 22–40

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. HÅLAND11, 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. ŠCIBAN23, J. SJENICIC24, A. STIPNIECE25, 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 Avifaunists,

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.

Abundance of Common Pochard breeding in Europe 23


19Department of Ecology, Faculty of Environmental Sciences, Czech University of Life Sciences, Kamycka 1176, CZ-165 21, Prague 6, Czech Republic.

20Department of Biology, University of Lund, Ecology Building, Lund, S-223 62, Sweden.21Severtsov’s Institute of Ecology and Evolution, Leninsky Avenue 33, Moscow 119071,

Russia.22Natural Resources Institute Finland, Yliopistokatu 6, FI-80100 Joensuu, Finland.

23Bird Protection and Study Society of Serbia, Vladika Cirica 24, RS-21000 Novi Sad, Serbia.24Society for Research and Protection of Biodiversity, Brace Potkonjaka 16,

BA-78 000 Banja Luka, Bosnia and Herzegovina.25Institute of Biology, University of Latvia, Miera Street 3, LV-2169 Salaspils, Latvia.

26Laboratory of Avian Ecology, Lithuanian Nature Research Centre, Akademijos Str. 2, LT-08412 Vilnius, Lithuania.

*Correspondence author. E-mail: [email protected]

Abstract

National accounts suggest that the Common Pochard Aythya ferina was an uncommonbreeding bird throughout western Europe before 1850. Extensions to the breedingrange in the late 19th century were potentially aided by the rapid development ofmanaged fish-ponds in eastern Europe, which provided suitable novel habitat at thattime. Expansion into western Europe followed in subsequent decades. Wetland andwaterbody eutrophication throughout Europe, which likely provided food and coverfor the birds, may have accelerated the rapid expansion from the 1950s until the early1980s. Widespread declines in the last 30 years, especially in eastern Europe, wherebreeding numbers are highest, are possibly linked to intensification and/orabandonment of freshwater fish farming and changes in water quality. Studies showthat Pochard gain fitness benefits from nesting in Black-headed Gull Chroicocephalus

ridibundus colonies and hence has been affected by major losses of European gullcolonies 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 theMediterranean region. Changing predation pressures (in some cases linked to invasivealien mammals) are also implicated in some areas. Relatively modest numbers breedingin the UK, France and the Netherlands have remained stable or increased over thesame recent span of years, confirming that different factors currently affect Pochardbreeding abundance throughout its range. We urgently need better informationrelating to key factors affecting Pochard breeding success and abundance, which iscurrently showing an unfavourable conservation status throughout much of Europe.

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

24 Abundance of Common Pochard breeding in Europe


The Common Pochard (hereafter Pochard)Aythya ferina is a numerous and widespreaddiving duck, which breeds largely infreshwater to the south of the tundraregion across the Palearctic from Iceland tothe steppe lakes of Mongolia and theDaurian region (Kear 2005). It wintersthroughout Europe, in northern Africaalong the Nile as far as Sudan, theMediterranean, Black and Caspian Searegions, and the Indian sub-continent,through to southern China, Korea andJapan (Kear 2005; Reeber 2015). Latestestimates put the global population atbetween 1.95 and 2.45 million individuals(Wetlands International 2016), whichsuggests it is as numerous as its ecologicalcounterparts in North America combined(the Redhead Aythya americana at 1.35million and the Canvasback A. valisineria

with 0.69 million; Wetlands International2016). Since the 1850s, the Pochard hasexpanded its breeding range north andwestwards, colonising Fennoscandia,Scandinavia, Britain and the Netherlands,and since the 1950s has spread intoMediterranean countries including Greece,Italy, Spain and North Africa (Bezzel 1969;Hagemeijer & Blair 1997). For much of thelast 150 years the species therefore appearsto have expanded and consolidated itsbreeding range within Europe.

More recently, however, the assessmentfor the European Red List of Birds 2015(BirdLife International 2015a), indicatedthat there were serious reductions in thedistribution and abundance of breedingPochard from the late 20th century onwards,resulting in the European population beingupgraded from IUCN Least Concern status

to Vulnerable on the basis of a 30–49%decline in breeding population size over thecourse of three generation spans (22.8 years;after BirdLife International 2015a). Thisreflects similar declines in numbers recordedon its wintering grounds, which after a longperiod of relative stability have decreased by 50%, to c. 150,000 birds in northernEurope between the late 1980s–2012, and to c. 600,000 in Central Europe, theMediterranean and Black Sea region slightlylater during the late 1990s–2012 (Nagy et al.

2014). The species therefore is now alsodesignated as being globally Vulnerable(IUCN 2015).

How could a species that has consistentlyshown 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 unfavourableconservation status? Clearly, overallpopulation size in relatively long-lived duckspecies can be affected by changes insurvival rate, but in the case of the EurasianWigeon Anas penelope it has recently beenshown that changes in annual reproductiveoutput may also have a major impact onflyway population size (Fox et al. 2016). It isdifficult to relate changes in Pochardabundance in specific breeding areas with changes in winter numbers anddistribution because many of the birdswintering in Europe may originate fromcentral 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 relativeabundance of the Pochard population



breeding in European countries now and in the recent past, to determine the existingdistribution of breeding birds across rangestates, to compare the colonisation historyfor Pochard in these countries and to assess recent population trends for differentparts of the range. We also sought tocompile published assessments of thefactors considered responsible for thediffering trends in breeding abundance, inan attempt to understand the underlyingcauses for the variation in trends, and toprovide recommendations for sympatheticmanagement of breeding habitat, to restorethe former breeding abundance of Pochardwherever possible.

Methods

Following a workshop convened at the Pan-European Duck Symposium in Hanko inFinland on 9 April 2015, national expertswere approached and asked to compileinformation on Pochard from nationalcount databases and reports, for as manyEuropean countries as possible, in order to develop a profile of the past breedingstatus, current breeding status and anestimated trend in the abundance ofbreeding pairs over the last 10–12 years for short-term trends and since the 1980sfor longer term trends. Although weattempted to assess changes in annualbreeding success and survival, these wererarely available because the Pochard is generally neither a well-studied noreffectively monitored species, except at theclassic 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 anyinformation relating to factors that mighthave specifically affected female survivaland reproductive output (e.g. predationpressure), as well as any changes in habitatquality that might influence the food supply, nesting cover and its overallattractiveness to the species for breeding.This resulted in the expression of muchopinion, but relatively few studies wereavailable to relate such changes directly toreductions in nesting abundance and/orbreeding success.

Results

Contrasting recent national trends

in breeding Pochard abundance

throughout Europe

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

The full list of national populationestimates and recent trends for thosecountries thought to support <1% of thetotal European breeding population areshown in Table 1, while Table 2 shows the data for the 15 countries thought tosupport ≥ 1% of Pochard breeding inEurope (data from BirdLife International2015b, modified in accordance with theresults of the review presented here).Trends in national breeding abundance overthe last 20–30 years are shown in Fig. 1,where it is evident that, amongst thecountries supporting > 100 breeding pairs,48% of 29 counties showed declines,



Tab

le 1

.R

epor

ted

natio

nal E

urop

ean

bree

ding

pop

ulat

ion

size

s of

Poc

hard

for

cou

ntrie

s su

ppor

ting

<1,

500

bree

ding

pai

rs (i

.e. <

1%of

the

tota

l Eur

opea

n br

eedi

ng p

opul

atio

n). D

ata

from

Bird

Life

Int

erna

tiona

l (20

15b)

, with

mod

ifica

tions

by

the

auth

ors.

Perc

enta

gech

ange

is n

ot in

dica

ted

for

coun

trie

s w

ith <

c. 10

0 br

eedi

ng p

airs

.

Co

un

try

Cu

rren

t p

op

ula

tio

n e

stim

ate

Sh

ort

term

po

pu

lati

on

tre

nd

Lo

ng

term

po

pu

lati

on

tre

nd

Pa

irs

% E

uro

pe

Peri

od

Qu

ali

ty%

Ch

an

ge

Peri

od

Qu

ali

ty%

Ch

an

ge

Peri

od

Qu

ali

ty

Lu

xem

bo

urg

1<

120

08–2

012

good

Alb

an

ia0–

5<

120

02–2

012

good

Ko

sovo

<10

<1

2009

–201

4m

ediu

mM

on

ten

eg

ro<

10<

120

02–2

012

poor

Sw

itzerl

an

d<

11<

120

08–2

012

med

ium

No

rwa

y<

15<

120

00–2

013

good

FY

RO

Ma

ced

on

ia<

20<

120

01–2

012

poor

Geo

rgia

Pres

ent

<1

??

Po

rtu

ga

l<

50<

120

08–2

012

poor

Gre

ece

30–8

0<

120

08–2

012

med

ium

Slo

ven

ia50

–100

<1

2007

–201

2m

ediu

mM

old

ova

100–

120

<1

2000

–201

0m

ediu

m–3

0 to

–40

2000

–201

0m

ediu

m–2

0 to

–40

1980

–201

0m

ediu

mA

ust

ria

130–

200

<1

2001

–201

2m

ediu

m0

2001

–201

2m

ediu

m0

1980

–201

2po

orB

osn

ia H

G10

0–20

0<

120

10–2

014

poor

?It

aly

150–

200

<1

2012

med

ium

–50

2000

–201

2m

ediu

m–2

5 to

–40

1980

–201

2m

ediu

mB

ulg

ari

a80

–250

<1

2005

–201

2m

ediu

mfl

uctu

atin

g20

00–2

012

good

+5

to +

2019

80–2

012

med

ium

Den

ma

rk28

0<

120

11m

ediu

m–2

0 to

–33

1999

–201

1go

od–5

0 to

–10

019

80–2

011

good

Arm

en

ia10

0–35

0<

120

02–2

012

med

ium

?S

lova

kia

300–

500

<1

2012

med

ium

–30

to –

5020

00–2

012

med

ium

+10

to +

2519

80–2

012

med

ium

Un

ited

Kin

gd

om

350–

630

<1

2006

–201

0m

ediu

m+

3619

96–2

008

good

+21

619

71–2

008

good

Belg

ium

500–

1,00

0<

120

08–2

012

med

ium

020

00–2

012

poor

+17

8 to

+56

719

73–2

012

poor

Est

on

ia50

0–1,

000

<1

2008

–201

2m

ediu

m–2

0 to

–50

2001

–201

2m

ediu

m+

20 to

+50

1980

–201

2m

ediu

mT

urk

ey

500–

1,00

0<

120

13m

ediu

m–7

0 to

–89

2000

–201

2go

od0

1990

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3po

orS

erb

ia87

0–1,

250

<1

2008

–201

2m

ediu

m+

1 to

+9

2000

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2m

ediu

m0

1980

–201

2m

ediu

mS

wed

en

700–

1,50

0<

120

08–2

012

med

ium

020

01–2

012

med

ium

–35

to –

9119

80–2

012

med

ium



Tab

le 2

.R

epor

ted

natio

nal E

urop

ean

bree

ding

pop

ulat

ion

size

s of

Poc

hard

for

coun

trie

s su

ppor

ting

≥1,5

00 b

reed

ing

pairs

(i.e

. ≥ 1

%of

the

tota

l Eur

opea

n br

eedi

ng p

opul

atio

n). D

ata

from

Bird

Life

Int

erna

tiona

l (20

15b)

, with

mod

ifica

tions

by

the

auth

ors.

Co

un

try

Cu

rren

t p

op

ula

tio

n e

stim

ate

Sh

ort

-term

po

pu

lati

on

tre

nd

Lo

ng

-term

po

pu

lati

on

tre

nd

Pa

irs

% E

uro

pe

Peri

od

Qu

ali

ty%

Ch

an

ge

Peri

od

Qu

ali

ty%

Ch

an

ge

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od

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ali

ty

La

tvia

1,50

0–2,

000

120

04m

ediu

m?

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to –

5019

94–2

004

med

ium

Neth

erl

an

ds

1,30

7–2,

621

120

08–2

011

med

ium

020

02–2

011

good

019

84–2

011

good

Hu

ng

ary

2,00

0–3,

000

120

00–2

012

poor

–60

to –

7020

00–2

012

poor

–60

to –

7019

80–2

012

poor

Lit

hu

an

ia2,

000–

2,50

01

2008

–201

2m

ediu

m–3

0 to

–40

2001

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ediu

m–3

0 to

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1980

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2m

ediu

mB

ela

rus

3,00

0–4,

000

120

09–2

010

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ium

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2001

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80–2

012

med

ium

Cro

ati

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5,00

01

2013

poor

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ran

ce

3,00

0–5,

000

220

09–2

012

med

ium

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0 to

–40

1985

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orG

erm

an

y4,

000–

5,50

02

2005

–200

9go

od–3

1 to

–10

019

98–2

009

med

ium

–21

to –

5019

85–2

009

med

ium

Po

lan

d2,

000–

11,0

003

2008

–201

2m

ediu

m?

–20

to –

100

1980

–201

2go

odU

kra

ine

7,00

0–12

,000

420

15m

ediu

mde

clin

ing

2010

–201

5m

ediu

mde

clin

ing

1980

–201

2m

ediu

mS

pa

in8,

300

420

07m

ediu

mfl

uctu

atin

g19

98–2

009

med

ium

fluc

tuat

ing

1980

–200

9m

ediu

mF

inla

nd

10,0

00–1

6,00

05

2006

–201

2go

od–6

9 to

–82

2001

–201

2go

od–5

1 to

–67

1986

–201

2go

odC

zech

Rep

9,00

0–17

,000

520

01–2

003

med

ium

+90

to +

110

2001

–201

3go

od–4

0 to

–50

1981

–201

3go

odR

om

an

ia20

,698

–28,

762

1020

08–2

013

med

ium

?R

uss

ia90

,000

–120

,000

4420

08–2

011

poor

–1 to

–10

2000

–201

0po

or



including European Russia, Czech Republic,Poland and Finland, which currentlyconstitute the four most important statesnumerically 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 breedingpairs, they contributed relatively little to theoverall totals. There were no discerniblegeographical trends, suggesting thatcontrasting trends reflect different pressureson breeding abundance in differentcountries.

Figure 1. Map showing the relative abundance of breeding Pochard Aythya ferina in each Europeancountry, as indicated by relative arrow/bar size. Abundance is measured in terms of the maximumnumber of breeding pairs recorded in the last 20–30 years (see Tables 1 and 2 for details). Countriessupporting <100 breeding pairs in this period are omitted. Arrows indicate countries with increasing(upward) and declining trends (downward), bars indicate no trends.

Trends in breedingnumbers

Positive

Stable

Declining

100–

999

pai

rs

1,00

0–4,

999

pai

rs

5,00

0–9,

999

pai

rs

10,0

00–9

9,99

9 p

airs

≥ 10

0,00

0 p

airs



Longer term trends in breeding

abundance and causes of change

In attempting to synthesise the“colonisation” by breeding Pochardthroughout Europe, it was extremelydifficult to determine precisely when thespecies first bred in each country. It wasquite impossible to determine whetherPochard recorded as breeding “for the firsttime” had merely returned after a period ofextirpation, had genuinely reproduced in apreviously unoccupied country, or indeedhad been present and undetected for manyyears. Hence, while many countries cite aspecific year for the first “recorded” case ofproven breeding, it is rarely possible todetermine if this did indeed represent the year in which the country was firstcolonised. There were some glaringanomalies; for instance, while it was clearthat European Russia, Ukraine and theBaltic States had all hosted breedingPochard from before the mid 1800s, Belarus(which is totally surrounded by these states)first recorded breeding in 1926. What doesseem evident is that Pochard were recordedas first breeding in Finland, Sweden andDenmark during the period 1849–1867 (seeSupporting Materials), so this does seem torepresent a northwestern extension of rangeduring the second half of the 19th century.Pochard are also thought to have reachedIceland and the United Kingdom at aroundthe same time. Numbers in these countriesdo not seem to have consolidated untilmuch later in the 20th century, however, andNorway did not experience its first breedingrecord until 1972. Nevertheless, it seemslikely from the combined accounts thatthere was also a major extension of the

range west into Germany (where the specieswas more confined to the east in formeryears), the Netherlands and the UK in thelate 1880s, which was consolidated byPochard colonising Belgium in the first halfof the 20th century, a period during whichthere was apparent expansion and increasingbreeding abundance in France and Spain.What does seem reasonably consistent wasthe more evident increase in breedingabundance across much of the range thatseemed to simultaneously occur from the1950s until the mid to late 1980s (seeSupporting Materials). This period ofincrease and expansion of the breedingpopulation of Europe was alsocharacterised by increases in the winteringpopulation 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 thefactors affecting the expansion of range andthe increase in breeding numbers thatoccurred within Europe starting in the early1800s, but more recent increases in nestingrange and abundance in the 1950s–1980swere linked in several countries to thecreation of artificial waterbodies (e.g.reservoirs constructed for drinking water,flood relief or hydro-electric power, or theflooding of mineral extraction sites such assand and gravel quarries), especially in areaswith nutrient-rich waters (see the summaryof reported factors contributing to Pochardbreeding increases in Table 3). This mayreflect a successful niche shift or merelyopportunism on the part of species whose



Increasing nutrient levels

Creation of reservoirs, fish-ponds and/or gravel pits

Hyper-eutrophication associated with agricultural runoff

Changes in water chemistry

Reductions in benthos biomass

Increased competition from fish

Excessive growth of emergent macrophytes

Abandonment of fish-ponds

Falling water levels (abstraction, climate change)

Loss of grazing to maintain short grass vegetation for nesting

Loss of submerged macrophytes

Intensification of fish pond management

Wetland destruction

Cutting of wetland vegetation

Reed-bed destruction

Fishing and hunting disturbance

Loss of Black-headed Gull colonies

Interactions with other alien species

Raccoon Dog predation

Raccoon predation

Red Fox predation

American Mink predation

Increased native predator pressure

No. of adverse factors identified

Be

lgiu

m

1

Au

stri

a

1

Bo

snia

an

d H

erz

eg

ovin

a

4

Sp

ain

6

Uk

rain

e

4

No

rwa

y

?

2

Fin

lan

d

?

5

De

nm

ark

1

Ge

rma

ny

3

Fra

nc

e

4

Lit

hu

an

ia

8

La

tvia

3

Cz

ec

h R

ep

ub

lic

6

Hu

ng

ary

5

Po

lan

d

6

Be

laru

s

8

Ru

ssia

9

To

tal

nu

mb

er

of

rep

ort

s fo

r e

ac

h f

ac

tor

fro

m

dif

fere

nt

co

un

trie

s

3

7

8

4

2

3

2

4

4

3

5

5

2

1

1

2

9

3

3

1

2

7

5

Tab

le 3

.Su

mm

aris

ed s

ugge

sted

cau

ses

of c

hang

es in

abu

ndan

ce a

mon

gst b

reed

ing

Poch

ard,

as

prov

ided

by

the

auth

ors

of th

is p

aper

.R

ed b

oxes

indi

cate

adv

erse

eff

ects

and

gre

en b

oxes

pos

itive

eff

ects

on

bree

ding

Poc

hard

. Cou

ntri

es a

re li

sted

acc

ordi

ng to

pop

ulat

ion

tren

ds (s

eeF

ig. 1

and

Tab

les

1 an

d 2)

.



former rarity merely reflected the scarcity ofits habitat. Either way, the expansion in thearea and number of suitable openwaterbodies through the creation andmanagement of artificial fish-ponds foraquaculture also had a major effect,especially in eastern Europe, where suchmanagement created optimal conditionswith high levels of fertilisation and regularwater table drawn down (Table 3). As itexpanded its breeding range westwards, thespecies seemingly took advantage of long-established extensive areas of fish-ponds, asin France for example, which had beenpreviously unoccupied. In more recenttimes, both the reduction in intensity and abandonment of such aquaculturepractices on the one hand, and increasingintensification of fish management on theother (in the sense that more feed, nutrientsand medication treatments are being appliedto the same bodies of water), have beenshown to affect breeding Pochard in France(Broyer et al. in press) and cited as the causesof declines in breeding Pochard in Austria,Czech Republic, Hungary, Poland andUkraine, as well as potentially elsewhere.Changes in water chemistry (especially dueto hyper-eutrophication of waterbodiescaused by agricultural runoff) are also citedin several countries as potentially beingresponsible for declining Pochard breedingnumbers, as are the knock-on effects ofthese on reductions in benthos biomass,excessive growth of emergent macrophytesand loss of submerged macrophytes (Table3). Direct competition between CommonCarp Cyprinus carpio and adult and ducklingPochard was found in some studies (Pykal &Janda 1994; Musil et al. 1997; Musil 2006).

Increased predation rates are often cited as acause of declines in Pochard nestingabundance, particularly those involvingintroduced alien species, such as RaccoonsProcyon lotor, Raccoon Dogs Nyctereutes

procyonoides and American Mink Mustela vison,but predation by Red Fox Vulpes vulpes andother native predators (including Wild BoarSus scrofa) were also cited.

Some of these effects may involvecomplex interactions with other species,such as the Black-headed Gull Chroicocephalus

ridibundus with which nesting Pochardfrequently associate. Pochard breeding inassociation with gull colonies apparentlybenefit from elevated breeding success andfemale survival in comparison withoccasions where they do not do so (e.g.Väänänen 2000; Väänänen et al. 2016). Sincethe Black-headed Gull is declining acrossmuch of the Pochard’s breeding range,authors from several countries proposedthat this trend has contributed to the localdecline of Pochard in their region. Despitethe association between gull colonies andPochard breeding success, however, wecannot reject the alternative explanation thata common factor is involved in the declineof both Black-headed Gull and Pochardwhere they co-occur. Abandonment ofgrazing of wetland vegetation on the onehand and excessive cutting of wetlandvegetation and loss of reedbeds on the otherhave also been implicated in the loss ofsuitable nesting cover, together with fallingwater levels and habitat destruction anddegradation (Table 3).

Table 3 indicates that some universalfactors may be behind the decline ofPochard across Europe, specifically

hyper-eutrophication of waters, loss of gullcolonies and predation by American Mink. Itis clear, however, that both the abandonmentand conversely the intensification of fish-farm management (which is largely restrictedin practice to eastern European countries)have also been cited as major causes ofchange in Pochard nesting numbers in thevery parts of the range where the species wasformerly most common, and is now showingthe greatest declines.

Discussion

Differences in trends between

countries

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

In contrast, the majority of the short andlong-term trends for the countriessupporting > 1,000 breeding pairs ofPochard are showing consistent declines(Table 2), several of major magnitude, which gives considerable cause for concern giventhe disproportionate contributions (> 90%)these states make to the European breedingpopulation. The numbers of Pochardbreeding in European Russia, for example,are considered to have declined by up to10% during 2000–2010 alone and the upper

estimate of population size has fallen by50% (although there remains considerableimprecision about the estimates comparedto those in smaller countries further west).Furthermore, we know relatively little abouthow the breeding numbers further east inRussia (i.e. outside of Europe and beyondthe scope of this review) have fared in thesame period, because many of the breedingbirds from these areas also contribute toEuropean wintering numbers, which havefallen dramatically in recent years (Nagy et al. 2014). Hence, whilst trends in breedingabundance in some of the countries withrelatively low numbers in the west of therange and those which have been recentlycolonised seem to be reasonably favourable,those in areas with greatest numbers andespecially those in the north and east of the range seem to be experiencing thegreatest rates of decline. Despite evidenceof recent increases in Mediterranean areas,longer term prospects are poor givenclimate change, increased water abstractionand invasive species, which will lead to loss of habitat, increased salinity andhypertrophy in remaining wetlands (Moss etal. 2009).

Management options to address

declines throughout the European

breeding range

Although it is important to stress that formany of the factors we lack hard evidencefor the ultimate causes of the decline in European breeding Pochard, thecongruence of factors reported from manydifferent countries supports the hypothesisthat there may be some common causes (seeTable 3). Regionally, macro-environment





conditions (such as poor weather duringlaying and incubation or drought) couldcontribute a common cause to explainregional declines. Pochard do seem to selectto nest on eutrophic (and in many casesephemeral) wetlands (Kear 2005), whichmakes them susceptible to nutrient andhydrological change given the relative rarityand unstable nature of such wetland types.Several authors noted the benefit of theprovision of new waterbodies in the formor reservoirs, gravel pits and fish-ponds ashabitat for breeding Pochard, which likelyfuelled the expansion of its range andpopulation size during the middle part ofthe last century. The eutrophication of suchwaters as a result of the increasing use ofinorganic fertilisers in agriculture from the1950s onwards was also cited as providingenhancement of suitable breeding habitatfor Pochard during their period of rangeextension and consolidation. Continuationof nutrient enrichment however typicallyelevates primary production, leading toovergrowth of reed-beds and willow scrubat cost to open water in such wetlands.Increased phytoplankton and water turbidityin remaining open water also restrictsbenthos and submerged macrophytecommunities (Ekholm & Mitikka 2006) andultimately the attractiveness to breedingduck species, including Pochard (Lehikoinenet al. 2016). The European WaterFramework Directive (WFD) adopted in2000 aims to restore good ecological statusto all surface waters by 2027, including themediation of such eutrophication effects,although there is wide agreement that such atimescale for delivery is overly optimistic(e.g. Hering et al. 2010). Hence, to restore

breeding Pochard populations at sites ofparticular significance to the species in theshort term (especially in protected areaswhere water quality issues are associatedwith catchment processes outside thejurisdiction of the protected area), specificsite-based remedial action plans are required to tackle problems associated with localwater quality. There also remain considerablechallenges associated with remediation and reinstatement of hyper-eutrophicatedwaters (e.g. Jarvie et al. 2013), so recreatingsuitable conditions for Pochard and otherbreeding waterbirds may present longer termconservation management targets in suchsituations. Meanwhile, successful wetlandrestoration projects at some key breedingsites for Pochard, as, for example, recentlyimplemented in the Baltic States, haveresulted in immediate increases in numbersof breeding as well as staging Pochard(Viksne et al. 2010), which gives hope thattargeted wetland creation and restoration cancontribute to local increases in nestingabundance.

Drought, especially in the south andsoutheast of Europe, has reduced thereliability of ephemeral wetlands appearingduring spring and summer, to whichbreeding Pochard are attracted. Althoughmanagement of hydrological abstractionfrom rivers and waterbodies can moderatesuch effects, in the face of changing patternsof precipitation and increasing temperaturesassociated with climate change, there is littlebeyond enhancing water management thatcan be done to safeguard importantbreeding sites for Pochard under suchcircumstances. Climate change acts intandem with water abstraction, resulting in

salinity increases at wetlands, renderingthem unsuitable for Pochard (Jeppesen et al.2015).

Changes in management of fish-ponds,either as a result of intensification (whichresults in the negative effects reported for eutrophication, or direct feedingcompetition between Carp and Pochardadults and young), or abandonment hasreduced the potential carrying capacity ofthis very important anthropogenic habitat tosupport breeding Pochard (e.g. Broyer et al.

in press). Although we lack firm scientificconfirmation that expert opinion hasidentified the key drivers of changes inPochard abundance correctly, it does seemthat changes in east European aquaculturehave played a disproportionate role in thedecline in numbers of Pochard breeding inthat part of the range. Nevertheless, thefuture appropriate management of thesesites does provide some options forrestoring nesting Pochard populations. Forinstance, agri-environmental and foodsecurity support mechanisms may beavailable to support sustainable andecologically friendly aquaculture productionin rural areas otherwise suffering pooremployment opportunities.

Predation on nests and incubatingfemales must also have an effect on thereproductive potential of the Pochardpopulation to reproduce successfully, evenwhere nesting conditions are perfect, andmany countries reported adverse changes inpredation levels due to several, ofteninteracting processes. In France, the WildBoar constitutes a problem and withincreases in their abundance anddistribution could become a source of

greater predation pressure in the future (e.g.Elmberg et al. 2009). However, most evidentin some other states were the presence of non-native predator species, such asRaccoon Dog, Raccoon and AmericanMink, all of which are able to access nestson islands, in reed-beds and on floatingvegetation. However, while the evidence forthe magnitude of the specific impacts ofthese three predator species on nesting duckspecies remains equivocal (e.g. Nordström etal. 2003; Kauhala 2004; Nordström &Korpimäki 2004; Väänänen et al. 2007;Kauhala & Kowalczyk 2011), there is goodevidence for the ecological impacts ofAmerican Mink and potential to prevent andmitigate the effects of this species (e.g.Bonesi & Palazon 2007). A rich literaturefrom North America shows that localpredator control in areas of high ducknesting densities increases nesting success(e.g. the pioneering work of Duebbert &Lokemoen 1980), but the intervention tendsto be financially costly, requires consistentsustained investment over much larger areasthan a single duck breeding site and is notlikely to have effects at the population level(Côté & Sutherland 1997). Other exoticspecies that may have potential influence onbreeding Pochard in France include theCoypu Myocastor coypus, Muskrat Ondatra

zibethicus, Red Swamp Crayfish Procambarus

clarkii and Catfish Silurus sp. as well as somenon-native exotic plants (e.g. Water PrimroseLudwigia sp.) which are all thought to exertan adverse effect on natural vegetation (A. Caizergues, unpubl. data). Bonesi &Palazon (2007) stressed the requirement forstrategic solutions and in particular forsensitising public and government agencies





to the need to respond nationally andinternationally to invasive alien species. Asof January 2015, the EU has implemented anew Regulation on Invasive Alien Species2015 (European Commission 2014) with themajor objective (under the EU’s BiodiversityStrategy Target 5 for 2020) to coordinateEU-wide actions to prevent, minimise andmitigate the adverse impacts of invasivealien species (IAS) on biodiversity andecosystem services, the economy and publichealth. The Regulation seeks to establishthree types of measures, namely: (i)prevention, (ii) early warning and rapidresponse and (iii) management of alreadyestablished IAS. Within EU member states,therefore, there is now a vital imperative onstatutory bodies to manage IAS (includingthrough international coordination), whichprovides a much needed imperative to tacklesome of the species considered here to be achallenge to the effective maintenance ofbreeding Pochard numbers.

Although Black-headed Gull colonies didnot improve Pochard reproductive successsignificantly at Grand-Lieu in France (B.Folliot, unpubl. data), loss of gull colonieselsewhere (which provide protection frompredators of eggs and hatchlings as a resultof the gulls’ communal mobbing behaviour,and have been shown to elevate Pochardreproductive success and female survival;Väänänen 2000; Blums et al. 2003) isfrequently cited as being the cause of lost or reduced breeding Pochard numbers.Although the Black-headed Gull populationis declining across much of Europe, localdeclines have been ascribed to differentcauses, e.g. in Latvia to a reduction infishing-related activities and mink farms,

where gulls could feed (Viksne 1997) and inDenmark to reduction in food availability atmink farms, changes in stock grazingintensity on grassland and the switch fromspring-sown to autumn-sown cereals(Bregnballe et al. 2015). For such reasonsassociated with large-scale land use andchanges in husbandry and aquaculture, thereis little short-term likelihood of restoringfood sources for nesting gull colonies.However, where changes in grazing pressureand cutting or loss of reed-beds areconcerned, local management to restoresuch features and enhance the attraction oflocal wetland nesting habitat are clearly highpriorities for the feasible sympatheticmanagement for breeding Pochard.

Finally, it should not be forgotten thatPochard are huntable in several eastEuropean states from 1 August, whichselects for breeding females and naivejuveniles prior to their departure to winterquarters. This, together with drowning infishing nets at the same stage in the annualcycle, also represents a source of avoidablemortality that could be mitigated that mayotherwise increasingly contribute to localpopulation decline.

Overall, therefore, it would seem that theexpansion in the range and size of thePochard population breeding in Europe wassupported in the middle of the last centuryby habitat creation and nutrient enrichment,which was not possible to sustain incontemporary landscapes. Continuedeutrophication of some waters and loss ofother wetlands (especially amongst fish-ponds that seem to have supportedparticularly high numbers) has contributedto the subsequent decline over the last 2–3

decades, potentially exacerbated by elevatedpredation rates from a suite of predatoryspecies that include some invasive alienspecies. There seems little doubt that localsympathetic site management can mitigatesome of these impacts where there is goodevidence for the local cause of declines in breeding abundance, but given themagnitude of the problem and the likelydiversity of local factors involved, it wouldseem that in the short term at least, we needto accept that the breeding population ofPochard in Europe in the coming fewdecades will be lower than in the recent past.In this respect, it is clear that appropriatemanagement is needed to stabilise thecurrent population trend, while research andmonitoring is concurrently implemented tounderstand the critical causes behind thedeclines and better track population change.There is a clear incentive to ensure thatthose sites that currently contribute themost important breeding concentrations ofthis declining species are effectivelyprotected and subject to optimalmanagement to maintain and enhancenumbers of breeding Pochard present.However, we must also face the reality thatthis is a species that breeds in small numberson large numbers of waterbodies andrestoration of the quality of those watersremains a priority if we are to restorebreeding numbers to former levels ofabundance. In this respect, the Pochardpresents us with a series of new natureconservation challenges, being a red-listedspecies which remains relatively commonand widespread, but nevertheless with arelatively narrow ecological niche. As aresult, it may not attract attention from

conservation NGOs and agencies in the first instance, yet it could decline torelatively low population levels relativelyquickly without clear managementprescriptions for its rescue. Moreover, thePochard may be experiencing additionalnegative demographic changes, which layoutside of the scope of this review, such asenhanced mortality outside of the breedingseason (e.g. through changes in huntingmortality, drowning in fishing nets andsuffering lead poisoning from lead shot in the environment), which may becontributing to current rapid declines in itsoverall abundance.

The species therefore deserves anintegrated flyway-wide approach to itspopulation management, taking intoaccount of all the interacting processeswhich limit and regulate its abundance,preferably under an internationally agreedflyway management plan. Such an approachis vital for understanding the effects onpopulation size of the factors discussedabove in relation to the breeding season,relative to those that operate at other criticalpoints through the remainder of the annualcycle (e.g. staging, moulting, wintering, etc.).Such knowledge is vital to balance andprioritise cost-effective conservation actionsto restore the species to more favourableconservation status. In this respect, it maybe a useful case study for other wetlandspecies in similar situations, where it is clearthat we require improved systems for thecollection of key baseline data (e.g. objectivemeasurement of annual national nestingabundance and breeding female survival in all countries, and of local factors that may be affecting these measures), in order





to support evidence-based conservationmanagement actions needed to maintainand ultimately restore local breedingabundance to previously higher levels. It isimportant that such coordinated researchand monitoring be instigated across its rangebefore the species approaches levels that areconsidered critically rare.

Acknowledgements

We are extraordinarily grateful to theenormous numbers of observers who havecontributed to our knowledge of breedingPochard over the generations, without whichthis account could not have been compiled.Thanks to Eileen Rees, Blas Molina, RichardHearn and an anonymous referee for theirsuggestions for improvements to an earlierversion of this manuscript.

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

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