A statistical examination of British bird observatories data

British bird observatories data are examined from a statistical viewpoint. Consideration is given to the forming of indices of migration volume which can be used to monitor fluctuations in breeding population levels. The collection of daily counts of grounded migrants is discussed and simple graphical techniques are used to explore migratory behaviour of some common nocturnal migrants. The timing of migration is found to be related to population size as measured by the Common Bird Census. Statistical models are fitted to sequences of daily counts of grounded migrants but migration indices developed from these models are shown to offer no significant improvements over those based on the timing of migration. Linear discriminant analysis is shown to be a useful method of linking weather data with observatories data, and statistical models are developed for daily counts which utilise weather information.