Collective animal migration.

Migratory movement is a strategy employed by a broad range of taxa as a response to temporally and spatially varying environmental conditions. Multiple factors can drive animal migration, including movement to hospitable environments when local conditions become unfavourable (such as to reduce nutritional and thermoregulatory stress), movement to find mates and/or breeding sites, and movement to minimise competition, predation, infection or parasitism. Migrating animals can often be seen to move together (Figure 1), sometimes in vast numbers. Despite this, the social aspects of migration have, to date, received very limited attention. Synchronisation of migratory behaviour among organisms, itself, does not imply that migrants utilise social information: synchrony is inevitable if there are relatively short windows of opportunity in which to move, or there exist sudden environmental changes that must be responded to. However, as will be outlined here, there is there is growing evidence that many migratory animals do utilise social cues, and that collective factors could shape migration in a variety of important ways.