You see, there was hardly ever a big storm on land that didn't bring at
least one or two new birds of some sort or other to the islands.
Naturally, too, the newcomers landed always on the first shore they
could sight; and so at the present day the greatest number of species
is found on the two easternmost islands nearest the mainland, which
have forty kinds of land-birds, while the central islands have but
thirty-six, and the western only twenty-nine. It would have been quite
different, of course, if the birds came mainly from America with the
trade winds and the Gulf Stream, as I at first anticipated. In that
case, there would have been most kinds in the westernmost islands, and
fewest stragglers in the far eastern. But your own naturalists have
rightly seen that the existing distribution necessarily implies the
opposite explanation.
Birds, I early noticed, are always great carriers of fruit-seeds,
because they eat the berries, but don't digest the hard little stones
within. It was in that way, I fancy, that the Portugal laurel first
came to my islands, because it has an edible fruit with a very hard
seed; and the same reason must account for the presence of the myrtle,
with its small blue berry; the laurustinus with its currant-like fruit;
the elder-tree, the canary laurel, the local sweet-gale, and the
peculiar juniper. Before these shrubs were introduced thus
unconsciously by our feathered guests, there were no fruits on which
berry-eating birds could live; but now they are the only native trees
or large bushes on the islands--I mean the only ones not directly
planted by you mischief-making men, who have entirely spoilt my nice
little experiment.
It was much the same with the history of some among the birds
themselves. Not a few birds of prey, for example, were driven to my
little archipelago by stress of weather in its very early days; but
they all perished for want of sufficient small quarry to make a living
out of. As soon, however, as the islands had got well stocked with
robins, black-caps, wrens, and wagtails, of European types--as soon as
the chaffinches had established themselves on the seaward plains, and
the canary had learnt to nest without fear among the Portugal
laurels--then buzzards, long-eared owls, and common barn-owls, driven
westward by tempests, began to pick up a decent living on all the
islands, and have ever since been permanent residents, to the immense
terror and discomfort of our smaller song-birds. Thus the older the
archipelago got the less chance was there of local variation taking
place to any large degree, because the balance of life each day grew
more closely to resemble that which each species had left behind it in
its native European or African mainland.
Public-domain text, read in full here on John Shaqi.
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