Predicting wader mortality and body condition from optimal foraging behaviour

In order to assess the future impact of environmental change, ecologists must be able to provide accurate predictions under new environmental conditions. The difficulty with this is that there is often no way of knowing whether the empirical relationships upon which model predictions are based will hold under the new conditions. As a consequence, such predictions are of uncertain accuracy. Behaviour-based models have been developed in an attempt to overcome this problem. These predict how individual animals will alter their behaviour in order to respond to future environmental change. Their central assumption is that, no matter how much the environment changes, each individual will behave in a manner that maximises its own fitness. Because of this, model animals are expected to respond to environmental change in the same way as real animals. By following the behaviour and ultimate fate of each individual, a behaviour-based model is able to predict the population consequences of the optimal decisions of individuals. These models should therefore provide a reliable means of predicting how animal populations will be influenced by environmental change. Behaviour-based models contain more parameters than traditional demographic models, but this does not mean that they will take any longer to parameterise and adapt to a particular situation. In fact they can often be developed much more quickly. I describe how behaviour-based models have been developed for non-breeding wader populations and how they have been used to predict the consequence of environmental change in terms of the mortality rate and body condition of waders.