National Geographic : 1938 Aug
BIRDS OF THE HIGH SEAS Albatrosses and Petrels; Gannets, Man-o'-war-birds, and Tropic-birds* By ROBERT CUSHMAN MURPHY CURATOR OF OCEANIC BIRDS. AMERICAN MUSEUM OF NATURAL HISTORY "They . . . that do business in great waters" (Psalm 107:23) BIRDS of only a few groups inhabit the high seas. Over the vast, far, oceanic reaches of a world surfaced mainly with water, the winged wanderers are likely to belong within one of three or four comprehensive orders. THE "TUBE-NOSED" SWIMMERS Among pelagic birds the Procellariifor mes, or members of the order of albatrosses and petrels, stand first. They are present in all salt waters from the Arctic basin to the uttermost shores of the south polar continent, including even such land-encom passed bodies as the Mediterranean Sea and the Gulf of California. They belong to the marine environment more fully than any other birds, for, like sea turtles and fur seals, many of them come ashore only for reproduction, remain ing at other seasons permanently in the wastes of waters, and even shying away from coasts so thoroughly that they may scarcely sight land other than their annual breeding stations. Not all of these creatures are far-roam ing, but some of them make yearly migra tions that are among the longest known. More and more it has become evident that each kind of these birds, like organisms living beneath the surface, is specialized in one way or another for particular types of ocean water. The curved expanse of the sea is not "boundless," as tradition holds. On the contrary, it is rather sharply divided by lines of temperature, wind belts, zones of varying rainfall and evaporation, and other agencies, into regions of different physico chemical characteristics, respectively inhab ited by different types of the surface life which constitutes bird "pasturage." SARGASSO A "WATERY DESERT" Thus the famed Sargasso Sea, and cor responding areas in the central parts of other oceans, are watery "deserts." The underlying depths may be rich in life, but the surface is warm and hence poor in oxygen, extremely salty because the water has been long exposed to the evap orating influence of sun and trade wind, and deficient in nutrient chemicals because of the great distance from land and the bounty of rivers. In such centers, moreover, the highly sa line and dense surface waters tend contin ually to sink, thus preventing decomposition products held in "cold storage" far below from rising to the upper layers. On the other hand, the encircling ocean current regions, particularly those close to continental coasts, are constantly or period ically enriched by the phenomenon known as "upwelling." Whenever a current di verges from a shore line, under the influence of a land breeze or for any other reason, the surface water removed must be replaced from below. OCEAN "PASTURAGE" ZONES The ascending masses are cool, usually rich in oxygen, and almost invariably teem ing with food products such as stored ni trates and phosphates, plant cells living and dead, and small animals such as copepod crustaceans which, by being eaten them selves, carry on the marine "key industry" of converting microscopic pasturage into fish, sea birds, and gigantic whales. For such reasons the boundaries between the ranges of sea birds are no less definite than those formed on the continents by such more obvious barriers as mountain crests, * This is the seventeenth article, with paintings by Major Allan Brooks, in the important GEO GRAPHIC series by outstanding authorities on the bird families of the United States and Canada. The entire series is now available in the National Geographic Society's two-volume Book of Birds, together with other notable articles, full-color portraits of 950 birds, 633 "bird biographies," and more than 230 photographs and bird migration maps. $5.00 postpaid in United States and Can ada. $5.50 elsewhere.