Cook Strait as a field for ecological study: Biogeography of Cook Strait seabirds
Murphy's pioneer studies of Southern Ocean seabirds led to the idea of circumpolar zonal distribution patterns correlated with the surface water masses. Thus many pelagic seabirds are completely or partially circumpolar in distribution, with northern and southern limits coinciding with, or at least paralleling in a rough way the oceanographic zones. The radial subdivisions of Southern Hemisphere land and sea have been more important than the concentric zones in con- trolling the distribution of some groups of birds, but even these have zonal limits within their own sectors.
New Zealand straddles the boundary between subtropical and subantarctic zones of surface water, the coasts of Auckland being subtropical and those of Otago/Southland subantarctic. Intermediate areas, including Cook Strait, fall in a convergence belt, where conditions may fluctuate markedly and show effects of both subantarctic and subtropical influence, emphasized by longitudinal cur- rents, and where mixing of different water masses may blur the distinctness of the convergence.