has once been taken in New York State. Pterodroma neglecta, the Kermadec petrel, has been once found dead in Britain (on 1 April 1908 near Tarporley in Cheshire). One Trinidad petrel Pterodroma arminjoniana, was driven to New York by the hurricane of August 1933, and possibly this close Atlantic relative of the Kermadec petrel may cross the equator fairly often, as it breeds on South Trinidad Island (only), which is fourteen hundred miles south of the equator, surely no very great distance for a petrel. One collared petrel Pterodroma leucoptera, a Pacific species, was shot between Borth and Aberystwyth in Cardiganshire, Wales, at the end of November or the beginning of December 1889. The last wandering tubenose is the black-bellied storm-petrel Fregetta tropica, a sub-antarctic species which was first collected off the coast of Sierra Leone and has also been taken in Florida. It seems likely that this last species may cross the equator fairly regularly, at least as far as the Tropic of Cancer.
One Pelecaniform wanderer has crossed the equator into the North Atlantic from South Africa—the Cape gannet Sula capensis, which may reach north to the Canaries.
From the western United States the California gull Larus californicus (which may be a race of the herring-gull, see here) winters fairly regularly to Texas, and thus (in our definition) to the North Atlantic region. Another gull which enters the North Atlantic, from more distant breeding-grounds, is the great black-headed gull, Larus ichthyaëtus of the Black Sea and farther east, which has reached Madeira and Belgium and has been seen in Britain about eight times.
Four exotic terns have wandered into the North Atlantic. The South American Trudeau’s tern Sterna trudeaui, has once reached New Jersey. On the east side Sterna balaenarum, the Damara tern of South Africa, has migrated across the equator as far as Lagos in Nigeria. Thalasseus bergii, the swift tern, breeds on the west coast of South Africa north to Walvis Bay, whence occasional individuals may sometimes pass north across the equator. The elegant tern Thalasseus elegans, of the Gulf of California, has accidentally reached Texas. And finally Gygis alba, the tropical, white, almost ‘transparent’ fairy tern breeds north in the Atlantic to Fernando Noronha, and therefore probably occasionally operates across the two hundred miles that would bring it to the North Atlantic, though there is so far no formal record of this. It has a wide distribution in all tropical seas, but is very much attached to, and does not often fly far from, its breeding-grounds; nevertheless R. C. Murphy (1936) ponders: ‘Since there are seasons when powerful southeast trade winds blow from Fernando Noronha across the equator almost as far as the mouth of the River Orinoco, speculation offers me no clue as to why Gygis has not succeeded in jumping the next gap and establishing itself in the West Indies.’
The remaining wanderers are from the North Pacific—auks from that cradle of the sub-order of auks. Aethia pusilla, the least auklet, has not actually reached the Atlantic, but one was found ‘halfway’ from the Pacific to the Atlantic, in the Mackenzie delta in May 1927. The ancient murrelet Synthliboramphus antiquus has been found three times in the Great Lakes area, but no farther east. Aethia psittacula, the paroquet auklet,* has actually reached the Atlantic by turning up in, of all places, Sweden: in December 1860 one was captured in Lake Vattern! If the least auklet has not reached the Atlantic, its congener Aethia cristatella, the crested auklet, has, for even if we reject (as most do) the alleged Massachusetts record, we must accept that of 15 August 1912 when one was shot north-east of Iceland. Finally Lunda cirrhata, the tufted puffin, was obtained by the great naturalist Audubon in Maine: other records from the Bay of Fundy and Greenland are erroneous.
FIG. 2c Bathymetrical sketch-chart of the Atlantic Ocean
CHAPTER 2 EVOLUTION AND THE NORTH ATLANTIC SEA-BIRDS
GEOLOGISTS DIFFER in their opinions of the origin of the Atlantic Ocean. The followers of the geomorphologist Alfred Wegener believe that it is a real crack in the earth’s crust whose lips have drifted away from each other, and this opinion is lent verisimilitude by the neat way in which the east coast of the Americas can be applied to, and will fit with extraordinary exactitude, the west coast of Europe and Africa. It must be stated that, while the present opinion of most geographers is that the resemblance of the Atlantic to a drifted crack is purely coincidental, this is not shared by all students of animal distribution and evolution, some of whom, find the Wegener theory the most economical hypothesis to account for the present situation.
Whatever the truth is, there is no doubt that the boundaries of the Atlantic, and their interconnections, have varied considerably; thus halfway through the Cretaceous Period, about ninety million years ago (during this long period nearly all the principal orders of birds evolved), there were bridges between Europe, Greenland and Eastern North America cutting the Arctic Ocean from the North Atlantic completely; and from then until the late Pliocene—perhaps only two million years ago—there was no continuous Central American land bridge, but a series of islands.
Our present knowledge of the tree of bird evolution owes much to Alexander Wetmore and his school, who have so notably added to our knowledge of fossil birds during the last twenty years, especially in North America. Birds do not appear very frequently in the sedimentary rocks—their fossil population does not generally reflect their true population in the same way as that of mammals is reflected. However, if land-birds are rare in the beds, water-birds are relatively common, and the periods and epochs in which all our sea-bird orders, and many of our sea-bird families and genera, originated are quite well known. A recent paper by Hildegarde Howard (1950), of the school of Wetmore, enables us to show a diagrammatic family tree of birds (Fig. 3), with special reference to sea-birds, and to collate its branching with the approximate time scale of the epochs, so cleverly established by geomorphologists in recent years from studies of sedimentation-rate and the radioactivity of rocks. It will be seen that the primary radiation of birds and the great advances into very different habitats consequent upon the first success of the new animal invention—feathered flight—took place in the Cretaceous period, the first birdlike feathered animals having been found as fossils in Jurassic deposits of the previous period, over a hundred and twenty million years old. In the Cretaceous period—the period of reptiles—ostriches were already foreshadowed, as were grebes and divers, and the pelican-like birds, and the ducks.
In the Cenozoic period—the period of mammals—the radiation of birds into all nature’s possible niches continued rapidly, especially in the first two of its epochs—Eocene and Oligocene—from sixty to thirty million years ago. In these epochs grebes can be distinguished from divers, and a bird of the same apparent genus (Podiceps, or, as the North Americans have it, Colymbus) as modern grebes has been found. Gannet-boobies of the modern genus Sula have been found in the Oligocene, as have cormorants of the modern genus Phalacrocorax. The only penguin fossils known are later—of Miocene age—but it seems probable that they share a common stem with the tubenoses, which would mean that their ancestors branched off in the Eocene. The tubenoses diversified in the Oligocene—from this epoch we have a shearwater of the modern genus Puffinus; and from the Miocene Fulmarus and albatrosses. The ducks started their main evolution in the Cretaceous, and by the Oligocene we find modern genera such as Anas (mallard-like) and Aythya (pochard-like); in the Pliocene we have Bucephala (Charitonetta)—one of the tribe of sea-ducks.
For the Lari-Limicolae, the order which includes waders, gulls and auks, the fossil record is rather indefinite, mainly owing to the difficulty of distinguishing the present families by bones
