Conservation assessment of the nominate subspecies of Eurasian Oystercatchers

1

Norwegian University of Science and TechnologyCentre for Conservation Biology

Conservation assessment of the nominate subspecies of Eurasian Oystercatchers

(Haematopus ostralegus ostralegus)

Martijn van de Pol

Phil Atkinson, Jan Blew, Olivia Crowe, Simon Delany, Olivier Duriez, Bruno Ens, Bernd Hälterlein, Hermann Hötker, Karsten Laursen, Kees

Oosterbeek, Aevar Petersen, Ole Thorup, Kathleen Tjørve, Patrick Triplet

2


Taxonomic status (Hockey 1996; Sibly & Monroe 1990)

Haematopus ostralegus ostralegus is the nominate subspecies of Eurasian Oystercatchers

Other subspecies are

H.o. longipes (Eastern Eurasia)

H.o. osculans (East Asia)

H.o. finschi (New Zealand) [often regarded as separate species]

Sometimes also

H.o. malacophaga (Iceland and Faeroe)

H.o. occidentalis (United Kingdom and Ireland)

Here these two are grouped within H.o. ostralegus

3


Life history

Medium sized, sexually monomorphic, pied Oystercatcher

Long term socially monogamous pair bonds

Polygyny (~1%)

EPY (~2%)

Highly territorial (nesting and feeding territory)

Extreme site-fidelity to breeding sites

Site-fidelity to wintering sites

Bi-parental care, equal shares

4


Life cycle

Timing of breeding varies strongly geographically

Single brooded with replacement clutches

Incubation 28 days, fledging 35 days

Semi-precocial and extended parental care (several months)

First two years low site fidelity

Sexually mature age 3 (adult plumage)

Delayed reproduction due to habitat saturation

Usually limited natal and breeding dispersal (<10km)

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range: 3-16 years

Age of first reproduction (years)

6


Life cycle

One of the longest living waders (record 43 yrs)

Generation time 11 years (IUCN), but probably higher

1st year survival ~0.5 [from day 30]

2nd year survival ~0.8

3rd year/adult survival ~0.9

Adult survival can drop to 0.7 in occasional years (cold and/or low food)

Reproduction ~0.3 with many years with almost no young intermixed with occasional good years

No known latitudinal gradients in vital rates (birds in north larger)

7


Environmental stochasticity

Atkinson et al. 2003

(Wash, UK)1984 1988 1992 1996 2000 2004

Van de Pol et al. 2006

(Schiermonnikoog, NL)

Fledglings / nestFled

glin

gs /

pair

Need many years of data…

Oosterbeek

et al. 2006

8


Feeding ecology Large prey spectrum

Mussels & cockles staple food

In summer Baltic tellin, ragwormand lugworm more prominent

Locally other bivalve, gastropod and crustacean species important

In agricultural fields leatherjackets and earthworms eaten

Most individuals specialize:

9


Habitat & migrationBreeding habitat

Mainly coastal areas (salt marsh, beaches, dunes)

In 20th century more inland (arable land, grassland, roofs)

Productivity salt marsh > agricultural lands > dunes ?

Overwintering habitat

Estuaries near the coast

Agricultural lands sometimes also used

Some populations resident, many migratory.

Long-distant migrant

In cold years or low food stocks → mass migration

→ atypical winter distribution

10


H.o. longipes

BreedingWinterBreeding & winterBarrier for natal and breeding dispersal?

Demarcation ostralegusand longipes subspecies

Distribution and (sub)populations

Atlantic

Continental

?

H.o

. ost

rale

gus

Iceland 4%

Faeroe 3%

UK & Ireland 31%

Nordic 18%

Low countries 43%

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ContinentalAtlanticAtlant. & Contin.

16 key sites

Max. counts

(O. Duriez, unpublished data)

Official 1% threshold

is 10,200 individuals

Winter migration and distribution

Migration routeRare migr. route

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Stroud et al. 2004:

1,020,000 (1990s)

Thorup 2006:

309,000-424,000 pairs

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United KingdomNetherlandsNorwayGermanyIceland

United KingdomGermanyNetherlandsIreland

31%

30%

11%

9%

4%

4%

3%3%

2%1% 2%

SwedenDenmarkFaeroe IslandsRussia FinlandOther

37%

21%

21%

8%

6%

3% 3% 1%

FranceDenmarkAfricaOther

Summer Winter

UK UK

GE

NL

IR

FRDK

NLNO

GE

ICSW

DKFA

AFR

+ most data available

+ most reliable data- less data available

- less reliable data

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Year

1975 1980 1985 1990 1995 2000 2005

Year

1975 1980 1985 1990 1995 2000 20050

25

50

75

100

125

150

0

25

50

75

100

125

150

Germany Denmark(Wadden Sea area only)

United Kingdom(including Northern Ireland)

NetherlandsB

reed

ing

Inde

xsummer 1996=100

No data for Norway (11%), Iceland (4%), Sweden (4%), Faeroe (3%), Russia (2%), Finland (1%)

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Year

1975 1980 1985 1990 1995 2000 2005

Year

1975 1980 1985 1990 1995 2000 20050

25

50

75

100

125

150

175

0

25

50

75

100

125

150

175

0

25

50

75

100

125

150

175

France Denmark(Wadden Sea area only)

Germany(Wadden Sea area only)

Netherlands

United Kingdom(Northern Ireland excluded)

Ireland(Northern Ireland included)

Win

ter I

ndex

Winter

2001 =100

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NetherlandsGermany

Denmark

0

100,000

200,000

300,000

400,000

500,000

1986 1988 1990 1992 1994 1996 1998 2000 2002 2004Year

Num

bers

Wadden Sea (Blew et al. 2007)To

tal w

inte

r num

bers

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2000s1990s1980s1970s

Bre

edin

g pa

irs

(x 1

000)

Win

terin

g bi

rds

(x 1

000)

252

100

200

300

400

500

367

Goss-Custard et al. 1995; Hulscher 1997

365

Thorup 2006 This assessment

Goss-Custard et al. 1996

200

400

600

800

1000

874

Rose & Scott 1997

1,020

816

Stroud et al. 2004 This assessment


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Bre

edin

g pa

irs

(x 1

000)

Win

terin

g bi

rds

(x 1

000)

252

100

200

300

400

500

367

Goss-Custard et al. 1995; Hulscher 1997

365

Thorup 2006 This assessment


200

400

600

800

1000

874

Rose & Scott 1997

1,020

816

Stroud et al. 2004 This assessment


2000s1990s1980s1970s

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Protection statusIUCN

>30% observed (or projected) decrease in:

10 years or 3 generations (=33 years)

whichever period is longer

“Least concern”(IUCN categorizes the whole H. ostralegus

species)

1. H.o. ostralegus(816,000)

2. H.o. longipes(100,000-200,000)

3. H.o. osculans(10,000)

IUCN should categorize per subspecies!

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Year

1975 1980 1985 1990 1995 2000 2005

Year

1975 1980 1985 1990 1995 2000 20050

25

50

75

100

125

150

175

0

25

50

75

100

125

150

175

0

25

50

75

100

125

150

175

France Denmark(Wadden Sea area only)

Germany(Wadden Sea area only)

Netherlands

United Kingdom(Northern Ireland excluded)

Ireland(Northern Ireland included)

Win

ter I

ndex

33 years

33 years

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Demographic and mechanistic causes

of population change

What has caused the strong (initial) increase over most of the 20th century?

Successful adaptation breeding inland?

More moist agricultural lands became available

Agricultural lands became more fertilized

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Demographic and mechanistic causes

of population change

What has caused the strong (initial) increase over most of the 20th century?


However numbers also increased in coastal areas (Goss-Custard et al. 1996)

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Demographic and mechanistic causes of population change

What has caused the strong (initial) increase over most of the 20th

century?


However numbers also increased in coastal areas

Hatching success high in 1930-60s and later decreased.

Successful adaptation, high productivity in coastal areas (source-sink dynamics) or both?

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Demographic and mechanistic causesMore recent decline in Netherlands:

Primarily caused by over-exploitation due to mechanical shell-fisheries (mussels and cockles).

Reduces (juv & ad) survival, primarily in cold winters (Atkinson et al. 2003; Ens et al. 2004)

Reduces reproductive output (low food stocks and body condition at start of breeding) (Van de Pol et al. 2006; Oosterbeek in prep.)

Shell-fisheries disturbs the soil and changes benthic fauna (Piersma et al. 2001)

Additional role reduced eutrophication

Reduces nutrients for shell-fish stocks (Phillipart et al. 2007; Ens 2006)

Additional role agricultural intensification

Frequent mowing reduces reproduction (Hulscher & Verhulst 2001)

Demographic cause: reproduction > survival?

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Demographic and mechanistic causes of population change

More recent decline Germany and Denmark:

Causes not well understood → need more research

Increase France:

Thought to have resulted from birds choosing to overwinter in France instead of Wadden Sea (Triplet and Maheo 2000)

Decline Norway(?):

Halving of number of (Norwegian) Oystercatchers migrating through Denmark form 1990s to 2000s (Meltofte et al. 2006)

Meltofte (2006) suggests that Norwegian population has decreased, but no recent surveys available and expert opinions disagree

Alternatively, Norwegian birds now overwinter in UK more often

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Threats (1)

Mechanical shell-fisheries (major threat) :

As discussed before

In UK also affected survival in mild years and does not result in mass migration

Aberrant moult patterns

Reductions in carrying capacity of estuaries can be large (e.g.estimated decrease of 30% due to cockle fisheries in Westerschelde)

(Rappoldt & Ens 2006)

Hand shell-fisheries:

Less detrimental as long as scale is limited(Atkinson et al. 2006; Stillman et al. 2001)

But effects on spring numbers have been reported (Norris et al. 1998)

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Threats (2)

Bait-digging

Strong local reduction in worm prey (Lambeck et al. 2006)

Can increase cockle mortality (Jackson & James 1979)

Mechanical bait-digging disturbs the soil (Lambeck et al. 2006)

Agricultural intensification

Some fertilization good, too much fertilization and pesticides is detrimental for earthworms (Duriez et al. 2005)

Frequent mowing reduces egg and chick survival

High cattle densities causes trampling of nests (Beintema & Muskens 1987)

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Threats (3)Eutrophication

Decreased eutrophication reduces shellfish productivity(Phillipart et al. 2007; Brinkman & Smaal 2004)

In turn, declining shellfish stocks have caused fishermen to overexploit the littoral mussel beds (Ens 2006)

Habitat loss

Last 300 years much habitat loss due to humans (Lambeck et al 1996)

National and EU legislation make habitat loss less ikely in the future

Even opportunities for habitat restoration (Eertman et al. 2002)

However sea level rise is resulting in increased erosion in UK (2-7% per year), but not in the Wadden Sea (Norris et al. 2004; Wolters et al. 2005)

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Threats (4)Climate change

Laying date has advanced with 8 days from 1965-2005 (BTO website)

Prey species sensitive to temperature (negative impact)

Cold winters that cause mass mortality are expected to be less common (positive impact)

Hunting

Most countries legally protected since 1980s or not hunted

However, in France substantial numbers are shot each year (1,800-2,000), especially in cold winters (8,000-17,000) (Trolliet 2000; Triplet 2000)

This may represent a major source of mortality and may have population consequences that have not yet been quantified

31


Threats (5)Human disturbance

Many types of anthropogenic disturbance (recreation, military, agriculture)

The effect of anthropogenic disturbance depends on the specific source, but are typically stronger than natural disturbances (Kirby et al. 1993)

Recreation is increasing

Could make areas previously suitable for roosting, feeding or breeding no longer profitable, but quantitative consequences hard to estimate

Parasites and diseases

Major unknown

No avian influenza (Munster et al. 2007)

Gut-parasites common (helminths); effects on vital rates unknown (Norris 1999; van Oers et al. 2002)

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Threats (6)Predators and competitors

Suggested foxes played role in decrease breeding numbers (Willems et al. 2005)

Pacific oyster (Crassostrea gigas) is non-native invasive species

Increasing strongly in numbers

Not eaten by Oystercatchers or other predators

Taking over mussel beds

Compete for same resources and may also eat larvae of cockles and mussels

However, might also facilitate re-establishment of new mussel beds(Cadée 2007)

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Recommendations for research (1)1. Improve surveys

We lack good surveys for the sparsely populated and large breeding areas in all Nordic countries, especially Norway (10% of world population and possibly declining)

2. Meta-population structure (breeding and winter movements)

Start long-term color-ringing and monitoring programs in main breeding area (UK, Norway, Germany, Denmark, Faeroe, Iceland)

Stronger focus on role inland breeding sites (source-sink dynamics)

Start winter color-ringing programs for main winter areas (Dutch delta, Germany, Ireland, France, Denmark);

Satellite track small groups of individuals

Include ringing data in EUring database, not very useful now

Analyze genetic structure of potential (sub)populations(van Treuren et al. 1999)

34


Recommendations for research (2)

3. Mechanistic causes decline Germany & Denmark

Stimulate color-ringing studies

Relate egg and chick survival to food availability

Relate local trends in winter numbers to habitat and food quality.

4. Demographic causes of population change

Most population models either focus on how winter-conditions affect survival or how summer conditions affect reproduction.

Awareness is growing that there can be important feedback between overwinter conditions and reproductive output

Such feedbacks advocates for demographic models that include both the summer and winter stage.

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5. Climate change

Existing models should be used to quantify the effects of sea level rise and habitat loss.

(Goss-Custard et al. 1995; Sutherland 1996; Rappoldt et al. 2004)

6. Recreation

Determine exact influence of human disturbance on breeding and non-breeding Oystercatchers

Determine the potential for habituation to specific types of disturbances

Preserve some areas without disturbance (e.g. in nature reserves) as reference area

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7. Skewed sex-ratios and effective population sizes

Suggested many winter-populations are strongly male-biased(Durell & Atkinson 2004; Durell 2006)

This means that effective population sizes are much smaller thanpreviously reported

However, estimates based on biometric sex-discrimination, which might be unreliable (van de Pol et al, submitted)

Mechanism of sex-ratio bias is unknown

Therefore, we need large scale DNA sampling of fledglings in breeding areas and adults at roosts

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Recommendations for management1. Mechanical shell-fisheries

Creation of small marine protected areas where shellfisheries are excluded does not seem to result in a redistribution of birds, and thus

are not a solution to the problem of mechanical shell-fisheries. (Verhulst et al. 2004)

2. Hunting

In cold winters Oystercatchers mass migrate to France from more northerly estuaries. Currently hunting is usually forbidden after several days of continuing frost, when large numbers of birds have already been shot.

International agreements should be made to temporarily stop hunting as soon as a cold spell is detected in northern Europe. This interdiction should last 1-2 weeks to let birds recover body conditions to return to their usual wintering grounds.

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Summary conservation statusMost abundant and best studied Oystercatcher (sub)species

Numbers have increased over most 20th century but have recently dropped with 200,000

Decline in Netherlands mainly caused by shell-fisheries, but this is now strongly restricted and numbers are expected to increase again

Cause of decline in Germany and Denmark not known, future less clear

Good data for Nordic countries (especially Norway) much needed

Overall status still of ‘Least Concern’

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AcknowledgmentsSupported by Rubicon fellowship of the Netherlands Organization for Scientific Research (NWO)Centre for Conservation Biology, NTNU TrondheimDorete Bloch, Hans Meltofte, John Atle Kålås, Svein-Håkon Lorentsen, Even Tjørve, Ingar Øien and the people at the Norsk Ornithologisk Forening for help

PDF of presentation & conservation assessment at www.MyScience.eu/Oystercatcher

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Conservation assessment of the nominate subspecies of Eurasian Oystercatchers

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