Where the abyss touches the sky: a Booby and Noddy ecosystem

The earth is made of two parts: Continent and ocean. And the bottom of the ocean … the deep part, not the part that is covered with what is really continent blanketed by a sea or by volcanic oceanic islands … is called the “Abysmal Mantle” because it is part of the earth’s mantle and lies in the abyss. But there is one place and one place only where the abysmal mantle rises above the sea: The Archipelago of Saint Peter and Saint Paul. This is in the Atlantic Ocean, pretty close to where Air France Flight 447 crashed in 2009.

Darwin visited the islands on his way to South America on the Beagle and he found something very interesting. In fact, the bit of text I’m about to show you from Darwin’s writings is among the most interesting in all of his work, if you think about it. And he did think about it. The story had already been developed in the early 19th century circles of Natural Historians that when an island was formed in the ocean, say by a volcano erupting, that it would first be colonized by certain plants, and later certain non-human animals, then later, by humans bearing coconuts and palms. And, in those days as today, most people would assume that a given ecosystem would have at its base some kind of plant or slime or lichen or something.

On St. Paul’s Island, Darwin found a terrestrial ecosystem that had boobys and noddys at its base. The booby and the noddy, two bird species, live on this island. There are no other birds and no mammals, nothing else large. Just these birds and a handful of invertebrates that rely on the birds directly or indirectly. The dominant life form seems to be the spiders, which feed on each other (as they do) and the ticks and moths which in turn feed on the birds. Oh, and then there’s the land crabs that hide in crevasses but frequently come out to … but wait, wait, why am I explaining this to you? Darwin does an excellent job of it.

The following text is from Darwin’s ornithology notes. These are notes that he probably wrote in a bunch of notebooks while on the return leg of the Voyage, which involved something like a year and a few months of mostly sailing or being somewhere uninteresting, during which time he had little else to do but get busy crossing the t’s and dotting the i’s. These are the notes that were transformed into his later writings on the Voyage, and they were studied and published in the mid 20th century by a Darwin scholar (see reference below).

Anyway, without further ado

Darwin on the Land of the Booby and the Noddy:

We found on St. Paul’s only two kinds of birds—the booby and the noddy. The former is a species of gannet, and the latter a tern. Both are of a tame and stupid disposition, and are so unaccustomed to visitors, that I could have killed any number of them with my geological hammer. The booby lays her eggs on the bare rock; but the tern makes a very simple nest with seaweed. By the side of many of these nests a small flying-fish was placed; which, I suppose, had been brought by the male bird for its partner. It was amusing to watch how quickly a large and active crab (Graspus), which inhabits the crevices of the rock, stole the fish from the side of the nest, as soon as we had disturbed the parent birds. Sir W. Symonds, one of the few persons who have landed here, informs me that he saw the crabs dragging even the young birds out of their nests, and devouring them. Not a single plant, not even a lichen, grows on this islet; yet it is inhabited by several insects and spiders. The following list completes, I believe, the terrestrial fauna: a fly (Olfersia) living on the booby, and a tick which must have come here as a parasite on the birds; a small brown moth, belonging to a genus that feeds on feathers; a beetle (Quedius) and a woodlouse from beneath the dung; and lastly, numerous spiders, which I suppose prey on these small attendants and scavengers of the waterfowl. The often repeated description of the stately palm and other noble tropical plants, then birds, and lastly man, taking possession of the coral islets as soon as formed, in the Pacific, is probably not quite correct; I fear it destroys the poetry of this story, that feather and dirt-feeding and parasitic insects and spiders should be the first inhabitants of newly formed oceanic land.

Darwin, C. R. 1845. Journal of researches into the natural history and geology of the countries visited during the voyage of H.M.S. Beagle round the world, under the Command of Capt. Fitz Roy, R.N. 2d edition. London: John Murray. With a bibliographical inroduction by R.B. Freeman.

The photo of the Brown Booby (Sula leucogaster) is from Wikipedia.