By far the most impressive of the sea-bird haunts are the breeding cliffs, where the different species are zoned vertically as well as horizontally. Whether the rocks be volcanic or intrusive or extrusive or sedimentary, we are sure to find Larus gulls breeding on the more level ground a little way back from the tops of the cliffs—fulmars on the steeply sloping turf and among the broken rocks at the cliff edge, puffins with their burrows honeycombing the soil wherever this is exposed at the edge of a cliff or a cliff buttress, Manx shearwaters or Leach’s petrels in long burrows, storm-petrels in short burrows and rock-crevices, razorbills in cracks and crannies and on sheltered ledges, guillemots on the more open ledges where they can stand; perhaps gannets on broad flat ledges or on the flattish tops of inaccessible stacks, cormorants with their nests in orderly rows along broad continuous ledges, shags in shadowy pockets and small caves and hollowed-out ledges dotted about the cliff, kittiwakes on tiny steps or finger-holds improved and enlarged by the mud-construction of their nests, tysties or black guillemots in talus and boulders at the foot of the cliff. These wild, steep frontiers between sea and land are exciting and beautiful. They probably house larger numbers of vertebrate animals, apart from fish, in a small space, than any other comparable part of the temperate world.
Not many sea-birds of the east Atlantic do not breed on cliffs; but the skuas nest on moors, and the terns and black-headed gulls nest on sand and shingle. Many of the Larus gulls, and recently the fulmar, are catholic in their taste in nesting sites, and may be found on moors and even sand dunes. Quite a large number of sea-birds can be inland nesters, even including tubenoses. Fulmars now nest up to six miles inland in Britain, and many of the Larus gulls at much greater distances. The black-headed gull, in particular, is often a completely inland species, since some individuals nest in England as far as they can from the sea, e.g. in Northamptonshire, and may never visit it except in casual search for food.
As we go south along the Atlantic seaboard of the Old World we leave behind in the Channel Islands and Brittany the last elements of certain temperate cliff-breeding sea-bird species—the gannet, lesser blackback, great blackback, arctic tern (only a casual breeder so far south), razorbill and puffin. South of the Bay of Biscay we encounter a large sub-tropical and tropical community of about forty species (a few of which belong to sea-bird families but which have become river-birds or inland birds), which is distributed in four main geographical regions—the Lusitanian coast (the Atlantic coast of Spain and Portugal), the Mediterranean, the Atlantic coast of Africa north of the equator, and the Atlantic Islands. These last comprise the Azores, Madeira (to which pertain the Desertas and Salvages), the Canaries and—near the equator—the Cape Verde Islands. Many species breed, of course, in more than one of these regions, though only the herring-gull (rather doubtfully the little tern and cormorant) breeds in them all.
Of the species in the table, the crested pelican Pelecanus roseus, the pigmy cormorant Haliëtor pygmeus, the Mediterranean black-headed gull Larus melanocephalus, and the lesser crested tern Thalasseus bengalensis breed on no North Atlantic shore, and the rare slender-billed and Audouin’s gulls, Larus genëi and L. audouinii, are primarily Mediterranean species. It will be noted that three tubenoses have established themselves in the Mediterranean, but that no less than eight species breed in the Atlantic Islands, which have a greater variety of species of this order than any other part of the North Atlantic.
The distribution of breeding sea-birds on these coasts is best illustrated in tabular form :
Of the four main groups of these Atlantic islands, Madeira and the Cape Verdes have probably the largest sea-bird communities, with ten or a dozen species each. One tubenose, the North Atlantic great shearwater, Puffinus diomedea, nests on all of them as well as on the Berlengas of Portugal. Bulwer’s petrel, Bulweria bulwerii, and the little dusky shearwater, Puffinus assimilis, also nest on all four island groups. The Madeiran fork-tailed petrel, Oceanodroma castro, nests on all but the Canaries. The Manx shearwater nests on the Azores and Madeira, but not yet farther south. The little storm-petrel reaches south to the Canaries (although in small numbers and probably to these Atlantic islands only). The rather rare soft-plumaged petrel, Pterodroma mollis, is believed to nest on Madeira; it does so on the Cape Verdes. The beautiful frigate-petrel, Pelagodroma marina, breeds on the Salvages (which belong to Madeira but are nearer the Canaries), the Canaries and the Cape Verdes.
The red-billed tropic-bird, Phaëthon aethereus, the brown booby and the frigate-bird (man-o’-war bird) do not appear farther north than the Cape Verdes. Here the cormorant, which had dropped out in Morocco, reappears as a new race, primarily South African. The bird communities of these islands are only moderately well-known. Most of the sea-birds nest on rocks whose comparative inaccessibility has been both a temptation and a deterrent to the visiting ornithologist. As for the coast of West Africa and the islands lying close to it, no organised investigation of the sea-bird communities of this difficult region has yet been made. We know that one group of species breeds on the Atlantic African coast to Morocco, but no farther south—the shag, herring-gull, the whiskered tern, probably the gull-billed tern, possibly the slender-billed gull. Farther south both white and pink-backed pelicans, Pelecanus onocrotalus and P. rufescens, and the grey-headed gull, Larus cirrhocephalus, reach the tropical sea-coast in some places, and the brown booby nests on at least one island off the coast of French Guinea. The Caspian tern, whose world distribution is, to say the least, peculiar, may have breeding stations on this coast, and the little tern, which we had left behind in Morocco, reappears as a separate race on the coast and rivers of the Gulf of Guinea.
The African darter, Anhinga rufa, reed-cormorant, Haliëtor africanus, and the African skimmer, Rynchops flavirostris, haunt the rivers and in places reach the coast; but they are not sea-birds: and on islands in the Gulf of Guinea the noddy and the white-tailed tropic-bird, Phaëthon lepturus, breed. It is suspected that the frigate-bird may nest on this coast, but its breeding-place has not been found. Neither has that of the bridled tern, Sterna anaetheta, or the sooty tern, S. fuscata, although both species are seen in considerable numbers. There is at least one other riddle: a population of the royal tern, Thalasseus maximus, haunts almost the whole coast of West Africa from Morocco to some hundreds of miles south of the Equator. Systematists have separated it from the West Atlantic population as a subspecies (albidorsalis), on valid differences, and it does not appear to leave this coast, yet no ornithologist has yet seen its nest or even its eggs.
Only in the tropical parts of the Atlantic are there still these distributional queries. In the temperate and arctic zones the breeding places of the birds are well-known and described. And with this little mystery we conclude our tour of the Atlantic, for we are back on the equator and can strike west to the St. Paul Rocks, where we began.
FIG. 2a The breeding sea-birds of the North Atlantic, arranged by five geographical regions. No species breeds in more than four. Number of species; see opposite page for actual species
The sea-birds of the North Atlantic can be listed in the form of a table (Appendix, see here), and plotted according to which parts of the ocean they breed in, in the form of a diagram (Fig. 2). For the purpose of completeness, the secondary sea-birds have been included, those belonging to families whose fundamental evolution has probably been non-marine (like anatids and waders) or which are only sea-birds in winter (divers and grebes). Only the more important of these are on the diagram, and they are not otherwise treated in this book. It is interesting that more than half of them are northern ducks which winter at sea, though usually within sight of shore.
It must also be pointed out that several species belonging to the families of primary sea-birds have secondarily taken to