This paper, and the following 5 papers, were presented at the RIN93 Conference on “Orientation and Navigation - Birds, Humans and other Animals.” This took place in Oxford in April, and included some 40 papers. Copies of the complete Proceedings, priced £25 for RIN members and £35 for non-members, are available from the Director.

A model avian compass is formed if magnetite crystals are included among the statoconia loading some of the hair cells in the vestibular system. The magnetite is used as a null detector to detect the direction in which the magnetic couple acting on the magnetic crystal is zero. The location of the north/south plane and the angle between the directions of the gravitational and the magnetic fields are detected at a single site.

Migratory directions of birds have long been assumed to be at least partly ‘innate’ that is, genetically determined. In recent years much progress has been made toward understanding the genetic basis of several components of the orientation system. An important distinction has to be made between a bird's ‘knowledge’ of which direction to migrate, and its ability to use certain compass systems to find this intended direction. Both processes, establishing an intended direction and the subsequent compass orientation, have a partly genetic basis. The present review will be concerned only with the first of these processes, and the way it allows evolutionary changes of migratory routes to occur.