Shorebirds
We have applied individual-based models to a wide range of environmental issues, including the effects of shellfishing and aquaculture,
human disturbance, habitat loss and the assessment of site quality.
This page summarises the range of sites and issues for which models have been developed.
Hover your mouse pointer over a site on the map for details of that case study.
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Baie de Somme
Background:
Shorebird feeding areas in the Baie de Somme are under pressure from
several anthropogenic and some natural factors. These include cockle
fishing, hunting, disturbance from tourism, increasing areas of cord
grass and raising of shore levels due to sedimentation.
Issue:
How will shorebird survival and body condition be affected by (1)
changing the area available for hunting (2) banning hunting of curlew
and oystercatcher (3) changing the number of people allowed in the
nature reserve (4) changing the area of cord grass and (5) raising
shore levels.
Modelling:
A model
was developed incorporating the four main shorebirds found on the Baie
de Somme (dunlin, ringed plover, curlew and oystercatcher) and their
invertebrate prey. Data on bird numbers was being provided by the
Syndicat Mixte pour l'Aménagement de la Côte Picarde (SMACOPI). Data on
invertebrate biomass densities and cockle stocks was being provided by
the Groupe d'Etude des Milieux Estuariens et Littoraux (GEMEL). Model
simulations explored the effect of various changes on shorebird
mortality and body condition.
Baie de Seine
Background:
The
area of intertidal mudflats available to overwintering shorebirds in
the Seine estuary decreased throughout the 20th century due to land
reclamation and to the development of the port at Le Havre. Further
loss of intertidal feeding areas will result from an extension of the
port at Le Havre, known as Port2000.
Issues:
Would the loss of intertidal mudflats, and the increase in disturbance,
resulting from Port2000 affect the numbers of shorebirds surviving the
winter in good condition? If so, would a proposed area of mitigation,
changing marshland back into mudflat, be sufficient to maintain
present-day levels of mortality?
Modelling:
A model was developed incorporating the three main shorebird species
found on the Seine (dunlin, oystercatcher and curlew) and five
invertebrate prey species. Bird count data were provided by the Groupe
Ornithologique Normand and invertebrate biomass data by the Cellule de
Suivi du Littoral Haut Normand. The model accurately predicted the
distribution of shorebirds around the estuary in winter. Simulations of
the effect of Port2000 and the proposed mitigation area are ongoing.
Shorebirds and shellfishing
Background:
The Wash supports an internationally important population of oystercatchers, and also important cockle and mussel fisheries. Mussels and cockles are the major prey of oystercatchers in the Wash. The abundance of these shellfish decreased greatly in the 1990s, and was associated with an increase in the mortality rate of oystercatchers.
Issues:
Was the increase in oystercatcher mortality caused by the decrease in shellfish abundance, and how could the fishery be managed to minimise any affect on birds?
Modelling:
A model was developed incorporating the oystercatcher and shellfish populations, and the climate. The numbers of oystercatchers were recorded from a national monitoring programme and the abundance and distribution of shellfish from routine shellfishery surveys.
Results:
The model accurately predicted the year to year variation in oystercatcher mortality, indicating that food limitation was causing birds to die. The model predicted how the creation of new mussel beds could decrease oystercatcher mortality rate.
Collaboration:
BTO, CEFAS
The Humber Estuary
Background:
The Humber estuary contains several ports and other industrial developments as well as holding important populations of a range of shorebirds. Sea level rise is predicted to reduce the area of mudflats in the Humber by up to 8%.
Issues:
Will habitat loss caused by sea level rise and port developments increase the mortality rate of shorebirds in the Humber estuary?
Modelling:
A model was developed incorporating nine shorebird species and five of their invertebrate prey species. The numbers of shorebirds were recorded from a national monitoring programme and the abundance and distribution of their prey from surveys of the estuary. The model predicted the amount of habitat loss at which shorebird mortality rates started to increase.
Collaboration: ABP Marine Environmental Research
Southampton Water
Background:
Southampton water contains a major port and several industrial developments, as well as supporting important populations of overwintering shorebirds. New developments can be important for local economies, but may reduce the quality of a site for shorebirds.
Issues:
How can behaviour-based models help to reduce these conflicts?
Modelling:
Southampton Water was used as a test site for the development of a multi-species shorebird model. The model was developed incorporating the important shorebird and prey species in the site. The numbers of shorebirds was be taken from a national monitoring programme and the abundance and distribution of their prey from surveys of the estuary. The model was be used to assess how much information is required to parameterise a multi-species behaviour-based model.
Funding and collaboration: ABP Marine Environmental Research
Poole Harbour
Background:
Poole Harbour supports nationally and internationally important numbers of wintering waders and waterfowl. It has been designated under a wide range of national and international legislation, most recently as a Special Protection Area. The harbour holds an increasingly busy port, accommodates a wide range of water-based leisure activities, and supports both licensed and unlicensed fisheries for fish, shellfish, crustaceans and ragworms. It also contains several introduced species, most recently the Manilla Clam, currently the dominant bivalve mollusc in many parts of the harbour.
Issues:
Does the disturbance caused by various human activities in certain parts of the harbour limit the number of overwintering waders that the Poole Harbour SPA can support?
Modelling:
A model was developed incorporating the quantity, quality and tidal availability of the birds’ intertidal food resources. The model contains populations of each of the key wader species in the harbour and estimates of the frequency, intensity, timing and location of disturbing activities.
Results:
The model was used to show that the presence of the non-native Manila Clam Tapes phillipinarum, even at the current low density, reduced the predicted over-winter mortality of oystercatchers in Poole Harbour.
Funding and collaboration: Natural England, University of Greenwich
Shorebirds and shellfish in Welsh Estuary Special Protection Areas
Background:
any estuaries around the UK are classified as Special Protection Areas (SPAs) for shorebirds. Conservation agencies have to monitor these estuaries to make sure there is enough food for the important shorebird species living there and that human activities on the estuary do not disturb the birds too much. We are developing models for three Welsh SPAs - the Burry Inlet, Traeth Lafan and the Dee Estuary - which contain large populations of cockles and are important wintering sites for oystercatchers and knot.
Issues:
There are three main issues. (1) What is the best way of monitoring the amount of food available to the birds in each estuary? (2) How much food is needed to support the oystercatcher and knot populations currently found in each estuary? (3) How much disturbance can occur on each estuary without affecting the birds?
Modelling:
In the past, cockle populations in each SPA have been sampled only for fisheries purposes. The surveys provide a good estimate of cockle stocks in the fished areas, but do not estimate the total stock throughout the site. We designed grid-based sampling schemes to estimate the abundance and location of cockles and mussels throughout each site and all three estuaries were surveyed. The data were used to develop individual-based models for each site.
Results:
The individual-based models showed how dependent oystercatchers and knot were on shellfish stocks at each site. They are now used as a tool to provide evidence when making decisions about the fishery
Funding and collaboration: Countryside Council for Wales, Environment Agency Wales
Exe estuary
Background:
The Exe estuary supports an important shorebird assemblage, but is also used extensively by people for recreation, shellfishing and bait-digging. These human activities may adversely affect birds by excluding them from preferred feeding areas, reducing the amount of time they have to feed and increasing their energy requirements when they take flight.
Issues:
How can the present-day quality of the Exe estuary for overwintering shorebirds be measured? Will site quality be affected by changes in the amount of disturbance from people?
Modelling:
A model was developed and used to assess site quality and to predict the effect of local (i.e. disturbance from
a cycle path) and global (i.e. climate change) environmental change on the survival of six species of
overwintering shorebirds on the estuary. Site quality on the Exe was compared with that on three
other estuary Special Protection Areas (SPAs) and predictions for the effects of climate change were compared
with predictions made for another southern U.K. estuary, Poole Harbour.
Results:
Simulations of increased levels of disturbance from a proposed cycle path along the side of the estuary predicted
that disturbance of upper mudflat areas was unlikely to affect shorebird survival but that increased disturbance
of nearby fields would reduce curlew survival. Shorebirds on the Exe estuary were far less seriously affected
than those in Poole Harbour by reductions in mean daily temperatures, loss of terrestrial habitats and simulated
sea-level rise. It was concluded that the Exe estuary is a high quality estuary and that the shorebird populations
modelled were less susceptible to climate change than those in Poole Harbour.
Funding: Natural England, European Union
Burry Inlet
Background:
The Burry Inlet is a large embayment in South Wales, bordered on its south side by the Gower peninsula. More than ten thousand oystercatchers migrate from their breeding grounds to the Inlet every autumn and spend the winter there feeding mainly on cockles and mussels. The cockle beds are also exploited by shellfishermen who fish all year round using traditional hand-gathering techniques. This can lead to potential conflicts between the interests of birds and shellfisheries, most famously in the 1970's, when thousands of oystercatchers were culled on the Burry in an attempt to reduce their impact on the cockle fishery.
Issues:
There have been mussel beds in the Burry Inlet for many years, but recently mussel beds began to form on top of one of the main cockle beds. This prevents shellfishing by traditional hand-raking techniques and may also smother and kill the underlying cockles. Removing these new mussel beds, known locally as 'mussel crumble', would benefit cockle fishermen but might be bad for the oystercatchers, which feed on mussels as well as cockles. At the request of the Countryside Council for Wales, we developed a model of oystercatchers, cockles and mussels in the Burry Inlet and used it to determine how important the mussel crumble was for the birds.
Results:
The model showed that the mussel crumble could be removed without affecting the oystercatchers when cockle stocks in the Inlet were high. If cockle stocks were lower than at present, the mussel crumble was more important to the birds and removing it would mean some birds would have to leave the Inlet during the winter months or face starvation.
Funding: Countryside Council for Wales
Menai Strait / Traeth Lafan
Background:
The Menai Strait is the site of the largest on-bottom, commercial cultivation of mussels in the UK. At the eastern end of the Strait lies Traeth Lafan, an area of intertidal sandflats designated as a Special Protection Area because of its large population of overwintering oystercatchers.
Issues:
Is it possible to identify new mussel-management practices that can reduce losses of mussels to oystercatchers, thereby increasing commercial profitability? What would the effect of such management be on the oystercatcher population?
Modelling:
A model was developed incorporating the quantity, quality and tidal availability of mussels on naturally occurring mussel beds and commercial mussel lays. The model also incoporated the commercial shellfish gathering activities, and the oystercatcher population.
Results:
The model accurately predicted the losses of mussels to oystercatchers on the commercial lays. This equated to one fifth of the value of the current commercial landings. Losses of harvestable mussels to oystercatchers can be substantially reduced by altering the shore-level and extent of the commercial lays. If younger mussels are sacrificed, reduced losses of large, harvestable mussels need not increase the oystercatchers’ mortality rate.
Funding and Collaboration: Natural Environment Research Council, University of Wales, Bangor, Myti Mussels Ltd., Deep Dock Ltd.
Strangford Lough
Background:
Strangford Lough supports an important population of oystercatchers and an occasional cockle fishery. The cockle is the major prey of oystercatchers in Strangford Lough and so cockle fishing reduces their food supply. Cockle fishing in the lough occurs at low tide when the birds are feeding and so can also disturb birds away from their preferred feeding areas.
Issue:
Would an increase in the amount of cockle fishing decrease the survival rate of oystercatchers?
Modelling:
A model was developed incorporating the oystercatchers, cockles and shellfishing. The numbers of oystercatchers and the abundance and distribution of cockles were obtained from surveys of the lough. The model predicted that the current low intensity of shellfishing was unlikely to be increasing the mortality rate of oystercatchers, but that large increases in shellfishing intensity could increase mortality.
Funding: Environment and Heritage Service of Northern Ireland
Bahia de Cádiz
Background:
The Bahia de Cádiz has a diverse range of habitats (e.g. mud and sand flats, saltpans, lagoons and fish farms) and overwintering shorebirds (e.g. black-winged stilt, avocet, Kentish plover, redshank and curlew). The Bahia also supports a wide range of human activities (e.g. shellfishing, recreation, fish farming and salt production), which can create or remove shorebird habitat, increase or decrease bird food supplies or disturb birds.
Issues:
How do the various human activities in the Bahia influence the mortality rate and body condition of overwintering shorebirds? How could changes in management practices improve the quality of the Bahia for shorebirds?
Modelling:
A model was developed incorporating the main shorebirds found in the Bahia de Cádiz and their invertebrate prey. Data on birds, their prey and habitats were provided by University of Cádiz. Model simulations explored the affect of various changes on shorebird mortality and body condition.
Funding and collaboration: European Union, University of Cádiz
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