Migration (migratory): Periodic movement of organisms between alternative habitats e.g. between areas for reproduction and one or more areas of non-reproductive activity, or between areas of foraging and areas used for other activities. Most migrations occur at predictable intervals triggered by stimuli e.g. unfavourable conditions. NB: Movements that do not include an obligatory return journey are classified as dispersal (Baretta-Bekker et al., 1992).