DEVELOPMENT OF INDIVIDUAL-BASED MODELS IN SHOREBIRDS

1. DEVELOPMENT OF INDIVIDUAL-BASED MODELS IN SHOREBIRDS

2. WASH 1972-75 High Water Mark Low Water Mark Intertidal mudflats and sandflats Proposed fresh-water reservoir

3. HOW WE THOUGHT ABOUT THE ISSUE Percentage starving over winter Decreasing area Increasing density Increasing competition

4. EMPIRICAL APPROACH? (i) It would be technically very difficult ? Percentage starving over winter 0 0 0 0 0 0 0 0 0 X X X X X X X X X X ? Increasing density

5. ..and (ii) the function would probably change after habitat loss Habitat of above average quality is lost Percentage starving over winter Habitat of average quality is lost Increasing density

6. THE QUESTION: HOW TO DESCRIBE THE DENSITY-DEPENDENT STARVATION FUNCTION - NOT ONLY AS IT IS AT PRESENT BUT HOW IT WOULD BE IF THE FEEDING ENVIRONMENT WAS CHANGED BY: Habitat loss Disturbance Shellfishing Sea-level rise Mitigation measures etc etc

7. EVENTUAL ANSWER: develop and test individual-based models using oystercatchers eating mussels on the Exe estuary

9. MUSSELS LOCAL ISSUE: WOULD HARVESTING MUSSELS AFFECT THE BIRDS?

10. NO EFFECT EFFECT Before After Percentage starving Increasing harvest/Decreasing food supply

11. DEVELOPMENT OF THE MODEL 1976-1996 Field work on interference and exploitation competition between oystercatchers for mussels

15. HOW THE MODEL WORKS MORE DETAILS AT: http://www.dorset.ceh.ac.uk/shorebirds/

16. ? Each bird decides each tide where, when and on what prey species it is best to feed http://www.dorset.ceh.ac.uk/shorebirds/

17. ? Each of the three displaced birds will choose the next best place in which to feed PRINCIPLE: birds in model use optimality decision rules (= fitness maximising) to decide how to respond to a change in their feeding environment – just as real birds do

18. Calibration period for overwinter mortality of adult mussel-feeding oystercatchers on the Exe Sept 1976 – Mar 1980

19. MORE NATURAL HISTORY WAS NEEDED: eg. feeding in fields over high tide

20. Predicted (retrospective) and observed increase in mortality 1980 - 1999 Calibration period:

21. CONCLUSION Winter mortality was density-dependent and the model postdicted it quite well

22. Applying the model to species other than Oystercatchers: some say that they take too long to parameterise NO LONGER SO! The models can usually be built, tested and applied within the time typically taken to conduct an EIA: i.e. 1 – 3 years

23. Bird energetics • Prey energy content • Functional responses • Interference functions • Food supply, exposure time, weather • Human activities eg.fishery MODELS CAN NOW BE BUILT AND TESTED VERY QUICKLY AS MOST PARAMETERS ARE IN THE LITERATURE: Obtained for the site being modelled Built into model – allometric functions

24. Applications to other species: what • we need to know • Bird energetics • Prey energy content • Functional response • Interference function • Food supply, exposure time and weather APPLICATION TO OTHER SPECIES - 1

25. Functional responses of oystercatchers eating mussels A

26. Predicting the asymptote of the functional response in shorebirds from 486 ‘spot’ estimates of intake rate • Intake rate (i.e. asymptote) depends on: • Body mass of bird • Mass of prey • R2 = 75.5% (log transformed data)

27. TEST OF PREDICTIONS FOR ASYMPTOTE y = x Curlew sandpiper Knot Redshank Grey plover Curlew Oystercatcher

28. Applications to other species: what • we need to know • Bird energetics • Prey energy content • Functional response • Interference function • Food supply, exposure time and weather APPLICATION TO OTHER SPECIES - 2

29. Interference function for stabbing oystercatchers: intake rate (mgAFDM/s) against density of birds

30. Predicting interference parameters from Stillman’s state-dependent behavioural model Prey size Bird size Handling time Running speed Interference function

31. Test of Stillman’s behaviour-based model: cockle-eating oystercatchers on the baie de Somme

32. Predicted and observed interference functions in cereal-feeding cranes. Predictions from Stillman’s model. Data: L. M. Bautista, J. C. Alonso & J. Alonso.

33. Applications to other species: what • we need to know • Bird energetics • Prey energy content • Functional response • Interference function • Food supply, exposure time and weather • Human activities APPLICATION TO OTHER SPECIES and SYSTEMS What do we need to measure?

34. RECENT DEVELOPMENTS • Risk of being killed by predators: • trade-off between foraging and safety • Multi-species models: • up to 9 species in one estuary • Multi-site models: • several estuaries across several countries

35. SOME EXAMPLES OF RECENT APPLICATIONS IN SHOREBIRDS Oystercatchers Shellfishing, disturbance 8 estuaries 4 countries Other shorebirds: Disturbance, habitat loss, 12 species bait-digging, Spartina10 estuaries encroachment, hunting 4 countries sea-level rise, monitoring estuary quality, mitigation Wildfowl Hunting, farming, wind 4 species farms >25 estuaries 4 countries Blue - examples used here

36. 1. OYSTERCATCHERS and SHELLFISHING How much shellfish should we leave after shellfish harvesting to ensure that the birds’ fitness is not reduced?

37. EXE: oystercatchers eating mussels Mortality Fail to reach target body mass With disturbance Range 1976-1999 % % No disturbance 0 55 110 165 kg/bird 0 55 110 165 kg/bird Prey biomass/bird left over after shellfish harvesting

38. ‘CRITICAL THRESHOLD’ or ‘ECOLOGICAL FOOD REQUIREMENT’ (food/bird) EXE ESTUARY ‘Critical threshold’ = 61kgAFDM/bird Percentage starving

39. Ecological requirement Multiples of (‘threshold’) kgAFDM/bird Exe Mussel 61 9.13 7.74 Bangor Mussel 50 9.62 6.42 Burry Cockle 44 9.27 5.58 Wash Cockle 20 7.93 2.52 Somme Cockle 33 6.56 5.03 * Taking into account wastage of shellfish flesh (stolen from the birds; winter loss of flesh from the shellfish themselves) Critical threshold or ‘Ecological requirement’ (E) Physiological requirement (P) kgAFDM/bird kgAFDM/bird * E/P

40. CONCLUSION: ecological requirements are 3-8 times larger than physiological requirements Because of interference and individual variation in efficiency, just leaving enough shellfish for oystercatchers after harvesting is not enough to ensure they survive in good condition - as Dutch experience confirms

41. 2. DISTURBANCE: people and raptors

42. SOMME : DISTURBANCE IN OYSTERCATCHERS ACTUAL AMOUNT: 1994-95 1996-97 1997-98 1997-98 including raptors Severe winter PERCENTAGE STARVING Mild winter DISTURBANCES PER HOUR

43. POLICY ADVICE: IN SEVERE WINTERS, DO NOT ALLOW OYSTERCATCHERS TO BE DISTURBED BUT IN MILD WINTERS, THEY CAN BE DISTURBED – but only up to about ONE disturbance/hour - including raptors

44. 3. SPREAD OF THE GRASS Spartina ON TO UPSHORE MUDFLATS

45. SOMME: Spartina spreads downshore at 20-40m per year into the feeding areas of dunlin High Water mark

46. Dunlin with Spartina spreading at 40m/year Mortality over winter % POLICY ADVICE: get rid of it! 0ha 100ha 200ha 0 years 5 years 10 years

47. 4. HABITAT LOSS and MITIGATION for it

48. PORT DEVELOPMENT: SEINE ESTUARY PORT (105 ha of mudflats) English Channel R. Seine High Water Mark MITIGATION: Convert reed beds into 50 or 100 ha of mudflats

49. DUNLIN in SEINE ESTUARY: Port development and proposed mitigation Before Port After Port 50hamitigation 100hamitigation 5% 0% 15% Failing to reach 75% body mass % Mortality % 0% Scenario Scenario

50. POLICY ADVICE: The mitigation is needed but should be 100ha if it is to fully effective