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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



where the cool Labrador current is met by a 

 barrier of warm water. Even some northern 

 species that penetrate this barrier and other 

 species that wander up into the North Atlantic 

 from below the equator never seem to get into 

 the Gulf. Indeed, the whole offshore bird list of 

 the Gulf, including accidentals, is only about one- 

 half that of the North Atlantic from which it is 

 drawn. The fact that the Gulf of Mexico is 

 almost a closed sea is perhaps a factor in this 

 result. In order to reach its waters, those sea 

 birds that are reluctant to fly overland must 

 thread their way through the maze of the Antilles 

 and pass through the comparatively narrow 

 portals of the Florida Straits or the Yucatan 

 Channel. An interesting contrast, bearing on 

 this point, is provided by the bird life of the 

 Pacific Ocean within the same latitudinal limits, 

 off the west coast of Mexico. Here, where there 

 are different patterns of currents, a greater 

 proximity to cool water, and no land barriers, 42 

 species of pelagic birds have been recorded, at 

 least 22 of them as breeders. 



The fact that the greatest superiority of the 

 waters off western Mexico is in breeding birds, 

 suggests that the nature of the associated offshore 

 islands plays an important part in limiting the 

 Gulf avifauna. With the exception of Cuba, most 

 of which is extralimital to this summary, all of the 

 islands of the Gulf lie within the limits of the con- 

 tinental shelf, and therefore outside the Oceanic 

 Province which is often considered the real habi- 

 tat of pelagic birds. The most remote of them 

 are small coral formation situated below latitude 

 25°. On the Campeche Bank there are seven 

 islets or atolls of this sort scattered at varying 

 distances of 70 miles or more from the mainland. 

 Among these is Cayo Nuevo, which, lying 125 

 miles in a northwesterly direction from Yucatdn, 

 has the distinction of being the farthest offshore 

 of all the Gulf islands. Alacran Reef, however, 

 although it is only about 80 miles north of the 

 Yucatan Peninsula, is the most distant from all 

 other land, including other islands. The only 

 other really offshore islets are the Dry Tortugas, 

 110 miles off the coast of peninsular Florida but 

 only 68 miles from the termination of the main 

 arc of the Florida Keys at Key West. 



Whether or not all eight of these offshore island 

 groups offer suitable nesting sites is not known. 

 The Tortugas, the Alacran Reef, and the Areas 



and Triangle Keys are the only groups that have 

 been reported on by ornithologists. The first 

 three are definitely known to support sea bird 

 colonies. The Triangle Keys are inhabited by a 

 rare tropical seal {Monachus tropicalis), but 

 whether it interferes with the colonization by 

 birds is open to serious question. None of these 

 islands is more than half a mile long or a few 

 hundred yards wide, and, in view of their small 

 numbers, the total area of dry land in the open 

 Gulf must be so limited that it imposes serious 

 restrictions on the breeding population of offshore 

 birds. The sooty tern, it is true, is alleged to 

 have once been established on Mujeres Island and 

 the noddy tern on both Mujeres and Contoy 

 Islands; but, although these islands are close in- 

 shore, they happen to be situated very close to 

 the edge of the continental shelf. 



Few aspects of field ornithology afford such 

 opportunities to the general observer as the dis- 

 tribution of pelagic birds over the Gulf. Our 

 present meager knowledge of this group of birds 

 is reflected in the extremely imperfect summaries 

 that follow. 



Sooty Shearwater Pvffinus griseus. 



An occasional visitant to the Gulf, reported 

 seven times from Florida (Pensacola; Pavilion 

 Key; Florida Keys and adjacent waters), once 

 from Texas (Aransas Bay, June 16-19, 1937), and 

 from adjacent Cuban waters (Matanzas). Curi- 

 ously enough, three of these occurrences were in 

 winter, when the species is engaged in its breeding 

 activities thousands of miles away in the Southern 

 Hemisphere. The dates of occurrence in the Gulf 

 proper range from December 29 to July 18 and 

 involve every intervening month except February. 

 The Texas record is substantiated by a photo- 

 graph, and one of the Pensacola records (that of 

 January 3, 1935) by a bird found dead on the 

 beach; the other reports are based upon sight 

 identifications, not all of which were positively 

 assigned to this species by the observer. Appar- 

 rently, there is no Gulf specimen extant. 



Audubon Shearwater Puffinus Iherminieri. 



A breeding bird of the West Indies, said to 

 occur more or less regularly in the Gulf, but 

 apparently not observed there alive since the time 

 of Audubon, who claims to have seen it in num- 

 bers in June off the western shores of Florida. 



