1. 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.
2. 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.
3. 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.
4. 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.
