PROPAGATION AND MIGRATION OF FOUR SPECIES OF STERNA
1963
Kullenberg, Bertil
This paper deals with the distribution and migrations of Sterna hirundo, S. macrura, S. hirundinacea and S. vittata. Primary importance is attached to the distribution and migration routes of S. macrura. The recent distribution of these Sterna-species is seen from the point of view of nourishment, climatological and hydrological factors nowadays and during the quaternary glaciation. S. hirundo and S. macrura seem to have developed from the same origin. The former is adapted to temperate climate; the latter to arctic and subarctic climate. S. macrura is a coast living bird though in subarctic and arctic territories also breeding at fresh water. Probably S. macrura has developed in the old Bering country and northwesterly North America and from there spread to eastern North America and northern Eurasia, i.e. in two main directions. So it was adapted to the long days of the arctic summer but was forced to go to the south during the northern winter. It is possible that S. vittata has developed from popu lations of S. macrura remaining in the antarctic and subantarctic waters during the northern summer. As one cause of the suspension of the migration back to the northern breeding terri tories one can point out the very rich plankton life in the surface water of the southern cold oceans. S. macrura is distributed continuously circumpolar and is not divided into races. At the antarctic and subantarctic islands well isolated populations of S. vittata have settled down; geogaphiraphical races have developed.
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