Bahia de Cádiz

36.439, -6.182


Grey plover, Pluvialis squatarola

Kentish Plover, Charadrius alexandrinus

Ringed plover, Charadrius hiaticula

Oystercatcher,Haematopus ostralegus

Bar-tailed godwit,Limosa lapponica

Black-tailed godwit,Limosa limosa

Little Stint,Calidris minuta

Redshank,Tringa totanus

Sanderling,Calidris alba


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.


The overall aim of this project was to provide for policy-makers and their scientific advisors a suite of field-tested predictive population models with which they can devise local and Europe-wide management plans for maintaining the biodiversity of migratory (wintering/on passage) coastal birds (waders and wildfowl) that feed on inter-tidal and, often, supra-tidal (supplementary) habitats. The original project objective was to achieve this by adapting, simplifying and parameterising two existing individual-based population models so that they could be applied rapidly to a variety of species whenever policy decisions were required and at any geographic scale. Both predicted the body condition and mortality rate over the non-breeding season of classes of individuals within the population. Both models assumed that, when responding to management-induced changes in their feeding environment, individual birds chose the options that maximize their intake rate. Both were individual-based, in the sense that they tracked the location, foraging decisions and ultimate fate of each individual within the population, and predicted population level responses to environmental change (e.g. mortality rate) from the behaviour and fates of individuals (e.g. the proportion of individuals which die). One model, the single-site wader model, was a single-site (e.g. estuary) model for the non-breeding season which had been developed, parameterized and extensively (and successfully) tested for one common European wader species. The other, the multi-site goose model, was a multi-site, Europe-wide model which had been parameterized and tested, in a preliminary fashion, for one common wildfowl species. The aim of the project was to build, test and define the utility of the models for a much wider range of species in order to rapidly provide, at whatever geographic scale required, bird population predictions for a range of policy options. The original objective of adapting two existing models was extended during the project, and instead a completely new model was developed capable of making predictions for both waders and geese, at either the single or multi-site scale. The new model can be applied to a much wider range of systems and issues than could either of the initial models. The new model is based on the same principles as the existing models and is also individual-based. It builds on the strengths of the existing models, and adds improvements where the previous models were limited.


Three key scientific advances were made during the project.

  • Development of a general individual-based modelling framework. The development of the new individual-based model has been one of the major scientific advances made during the project. The new model has the following advantages over the initial models. (i) It is much more flexible than the original models and so can be applied to a wider range of environmental issues. (ii) Using a single model for both geese and waders highlighted the similarities between these systems, rather than differences. (iii) The new model has been developed in a more general way than the previous models and so it not simply restricted to waders and geese, increasing the potential application of the model in the future.
  • Development of a general equation to predict the feeding rate of waders. The project showed that the a simple equation could be used to predict the feeding rate of wading birds feeding on a range of prey species. Feeding rate is one of the most important parameters in the model. All that needs to be known is the mass of the wading bird species, and the mass and abundance of the prey. This breakthrough meant that wader models could be developed much more quickly and for a wider range of species than would have been possible if feeding rate needed to be measured for each new wader and prey species.
  • Rapid application of models to real-world issues. If individual-based models are to be valuable tools for advising policy, they must be developed within a relatively short time span (e.g. a few years) and produce realistic predictions. Three site-specific multi-species wader models (Bahia de Cadiz, Spain, Baie de Somme, France and Exe Estuary, England) and a multi-site brent goose model (throughout western Europe) were successfully parameterised using data collected or collated during the four years of the project. The models successfully predicted much of the observed behaviour (e.g. amount of time spent feeding, rate of consuming food) and ecology (e.g. distribution between habitats) of the birds in the real systems. They were also used to answer a wide range of key site or system specific policy issues (e.g. hunting, disturbance, habitat loss of saltpans, fish farms, intertidal vegetation and sandflats). The successful parameterisation, testing and application of the wader and goose models is one of the key scientific advances made during the project, because it shows the potential of the approach to address European coastal issues.

The site and system-specific wader and goose models predicted the effect of a wide range of environmental issues (e.g. disturbance from people, hunting, habitat loss, sedimentation, encroachment of saltmarsh vegetation onto mudflats) on the survival and body condition of birds. These specific predictions are detailed in the report. In addition, the following more general policy recommendations can be derived from the results of the project.

  • Monitor bird food reserves as well as bird numbers. Estuary managers are often required to monitor the quality of a site for important bird species or to assess how potential changes to a site may influence site quality. The conservation importance of an estuary is often measured in terms of bird numbers using the estuary, but monitoring numbers is not necessarily a reliable way of assessing changes in site quality. In particular, this is because the numbers of birds using a site depend not only on the conditions at the site, but also the conditions at other sites both within the non-breeding and breeding seasons. Changes in the food supply can be used in combination with bird numbers to determine whether any decline in bird numbers is likely to reflect a problem on the site itself. Decreasing bird numbers in combination with a decrease in the amount of food would indicate that the problem was within the site, whereas decreasing bird numbers without a decrease in the food supply would indicate either that the problem was not limited food within the site, or that the decrease in bird numbers was due to factors outside of the site. A policy derived from these predictions would be to establish a monitoring programme to record the abundance of food on sites at the start of winter as well as continuing the usual procedure of monitoring bird numbers.
  • Monitor the use of marginal habitats and feeding times. The models developed during this project all predicted that birds fed in the most profitable and safest places and times when feeding conditions were good and survival rates high, behaviour which mimicked that of real birds. In contrast, birds were predicted to feed more in marginal habitats or at more risky times when feeding conditions were poorer, again behaviour which mimicked that of real birds. A possible policy would be to establish a monitoring programme to detect such changes in the behaviour of bird populations as an early warning that survival rates are likely to be falling. This approach would pick up possible detrimental changes on a site before increases in mortality rate could be detected through traditional approaches based on bird ringing programmes, increasing the chance that management can be implemented to improve conditions before bird survival declines greatly.


  • Maintain a network of sites. The multi-site models predicted that birds emigrated from a site when the feeding conditions declined on the site. The consequences for the population depended on whether emigrating birds were able to find and survive on an alternative site. Birds could not survive if they did not have the energy reserves to successfully fly between the two sites (i.e. alternative sites must be relatively close together). A simple policy derived from this prediction is that wherever possible a network of high-quality sites should be maintained. This maximises the chance that emigrating birds are able to find and survive on an alternative site, if conditions deteriorate on their initial site.


  • Include terrestrial habitats in conservation areas. Birds were predicted to use terrestrial habitats when feeding conditions declined on their intertidal habitats, a pattern also observed in real birds. For example, brent geese in northern Europe fed on grass when intertidal Zostera and algae biomass declined during winter. Waders consumed more earthworms from terrestrial fields when intertidal food was depleted in late winter. These terrestrial habitats are often critical to the survival of waders and geese, even though they are often considered as marginal habitats. These habitats are often excluded from the designation of Special Protection Areas, but this means that vital habitat is not being protected and as a result may be lost to building developments, or suffer high disturbance levels. A simple policy derived from these predictions is that wherever possible conservation areas should include the terrestrial habitats around estuaries as well as the intertidal habitats of the estuary itself. This would ensure that the full range of habitats required by birds are protected.

The model developed in this contract provides a means for predicting the effects of environmental issues on the survival and body condition of wading birds and wildfowl. As such, it is a tool which can be used by decision-makers concerned with the management of the coastal zone throughout Europe, whether they represent governments, fisheries organisations or nature conservation bodies. The model also provides the basis for further research into the interaction between coastal birds and their environment, and could be expanded in a number of directions, including application to the breeding season and to species other than waders and geese.

Funding and Collaboration

European Commission. Project number: EVK2-2000-00612

Related Paper

Stillman, R.A., Caldow, R.W.G., le V. dit Durell, S.E.A., West, A.D., McGrorty, S., Goss-Custard, J.D., Pérez-Hurtado, A., Castro, M., Estrella, S., Masero, J.A., Rodríguez-Pascual, F.H., Triplet, P., Loquet, N., Desprez, M., Fritz, H., Clausen, P., Ebbinge, B., Norris, K. and Mattison, E., 2005. Coastal bird diversity. Maintaining migratory coastal bird diversity: management through individual-based predictive population modelling, Centre for Ecology and Hydrology, Winfrith Newburgh, Dorset.