The extent of dispersive movement behaviour in Australian vertebrate animals, possible causes, and some implications for conservation

We review categorizations of, and published evidence for, large-scale or dispersive movement in Australia's vertebrate fauna. For the purposes of this paper, dispersive movements are defined as any large scale movements, relative to an individual's territory or to the population breeding range. A continuum in dispersive behaviours can be recognized between regular annual migration and less regular more opportunistic and either more or less extensive re-colonization movements. We argue that dispersive movements can be explained in terms of individuals maximizing Darwinian fitness through optimizing net energy intake traded off against mortality risk, as these vary over space and time. We find that migration, nomadism and other forms of dispersive behaviour can be considered to differ, not in type, but merely in degree. Our review revealed evidence of dispersive movement for 36 (16%) freshwater fish species, 2 (1%) frogs, 5 (0.6%) land and freshwater reptiles, 7 (100%) marine reptiles, 342 (51%) land and freshwater birds, 88 (56%) marine birds, 27 (8%) land and freshwater mammals, and 28 (50%) marine mammals. The Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act) is the Australian Government's main legal instrument for the conservation of biodiversity. While it recognizes, and has special provisions for, international migratory species, the Act does not recognize the special conservation challenges of continental dispersive fauna. The continental dispersive fauna not recognized by the Act includes 246 bird species. We conclude that the EPBC Act needs to be amended to explicitly account for the national conservation responsibilities of the Australian Government with respect to dispersive fauna.