Trends of migratory and breeding bird populations in the Wadden Sea. Karsten Laursen Aarhus University, Institute of Bioscience, Denmark

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1 Trends of migratory and breeding bird populations in the Wadden Sea Karsten Laursen Aarhus University, Institute of Bioscience, Denmark

2 Thanks to John Frikke and Bo L. Christiansen for photos Jan Blew and Kees Koijberg for data and figures Joint Monitoring Breeding Bird Group & Migratory Bird Group Hundreds of volunteer field counters

3 Content Introduction Methods Trends of migratory bids Trends of breeding birds Conclusions

4 The Wadden Sea a global cross road for migratory birds and an important breeding site The East- Atlantic Flyway

5 The counts are organised in four sections Blåvand DK - Denmark D - Schleswig-Holstein D Niedersachen/Hamburg NL The Netherlands Den Helder

6 Monitoring Program for migratory birds Synchronous Counts (January + 1 other month): 179 count sites (562 counting units) Springtide Counts (every 15 days, 25 per year): 60 counting sites (223 ST counting units) Goose Counts in March, May and November Aerial counts of moulting Shelducks (Jul./Aug.) and Eider (Jan.)

7 The best scenic view is from an aircraft More than 250 counts from aircraft in the Danish part

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9 Sønder Ho

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14 Comparison between counts from ground and aircraft Wildlife Biology 2008 Shelduck Oystercatcher

15 Knot ca ca ca

16 Estimation of trends Blue: bird number counted Light blue: added number (estimates calculated for missing counts, using UINDEX)

17 Barnacle goose

18 Index Barnacle goose 300, , , , ,000 50,

19 Trends of barnacle goose in the four Wadden Sea sections

20 Wigeon

21 Wigeon Index 180, , , , ,000 80,000 60,000 40,000 20, Number (x 10,000) Eelgrass index

22 Trends of wigeons in the four Wadden Sea sections

23 Eider

24 Eider Index Number R² = Mussel stocks (tonnes)

25 Trends of eider in the four Wadden Sea sections

26 Knot

27 Index Knot 300, , , , ,000 50,

28 Trends of knot in the four Wadden Sea sections

29 Arctic tern

30 Arctic tern Number

31 Arctic tern Birds breeding in Greenland winters in the southern Atlantic Ocean Birds breeding in the Wadden Sea winters in the southern Indian Ocean km km Fijn m.fl Ardea

32 Long-term trends of 34 migratory species J.P. Keldsen, Ornit DK 6 species increase (18 %) 12 species are stable (35 %) 16 species decrease (47 %)

33 Common drivers: food Fish (n = 4) Omnivorous (n = 1) Other invertebrates (n = 8) Plants (n = 6) Shellfish (n= 4) Worms (n = 11) Indicator Food

34 Common drivers: feeding habitat Beach & offshore (n = 3) Tidal (n = 21) Coastal grassland (n = 3) Saltmarsh (n = 7) Indicator Feeding Habitat

35 Also tidal height matters Feeding on tidal flat Feeding on saltmarsh

36 Conclusions on migratory birds Most species are declining - feeding on mussels, feeding in the tidal zone (some species) - wintering in Europe Few species are increasing - feeding on saltmarsh and grassland (some species) - breeding in the arctic and wintering in Africa Tidal amplitude affect migratory birds (sediment and climate?) Conditions in the Wadden Sea affects populations outside AARHUS UNIVERSITET

37 Breeding birds Annual counts in 56 census areas and of colonial species Total counts every 6 th (former 5 th ) year

38 Overview of breeding bird monitoring

39 Long term trends of 35 breeding species - since species increase (29 %) 2 species are stable (6%) 17 species decrease (49 %)

40 Types of trends and species

41 Trends of breeding birds in the four Wadden Sea sections during 20 years Hans H. Larsen

42 Summary of trends reflected by QSR-reports Eigil Ødegaard

43 Four species showing contrasting development Steen E. Jensen

44 Assessment of breeding success Eigil Ødegaard Thorup & Koffijberg 2015

45 Drivers for population changes Breeding success (Oystercatcher, Avocet, Arctic Tern) Annual survival (Eider, Hen Harrier, Black-headed Gull) Predation risk and flooding Food limitation during the chick-rearing period Land use, lowering of water level John Larsen

46 Conclusions for breeding birds Most species are declining Consistent development since Mostly effects within the Wadden Sea (breeding success, predation risk, food limitation, land use) Few external effects (annual survival (?), climate) AARHUS UNIVERSITET

47 Over all conclusions An effective monitoring scheme for birds (among the best in the world) Half of the migratory species are declining Half of breeding birds are declining Most of the effects lie, probably, within the Wadden Sea (breeding success, predation, food limitation) Some effects lie outside the Wadden Sea (climate) Some are unknown (effect of sediment changes) AARHUS UNIVERSITET