GCSE required practical. Resource to measure the population size of a common species -indoors!

Measuring the population size of a common species in a habitat is a required practical for GCSE. Personally i love fieldwork, but we will all be in a situation when we have planned to teach this, but it is raining outside! Also there is always that one class that you really do not trust. This activity will help you still do that lesson, but indoors. It is not a computer simulation but involves real ecological techniques.