Science in Arcady | Page 6

out, this particular bullfinch happened to have
in his crop several undigested seeds of European plants exactly suited
to the bullfinch taste; so when he died on the spot, these seeds,
germinating abundantly, gave rise to a whole valleyful of appropriate
plants for bullfinches to feed upon. Now, however, there was no
bullfinch to eat them. For a long time, indeed, no other bullfinches
arrived at my archipelago. Once, to be sure, a few hundred years later, a
single cock bird did reach the island alone, much exhausted with his
journey, and managed to pick up a living for himself off the seeds

introduced by his unhappy predecessor. But as he had no mate, he died
at last, as your lawyers would say, without issue.
It was a couple of hundred years or so more before I saw a third
bullfinch--which didn't surprise me, for bullfinches are very woodland
birds, and non-migratory into the bargain--so that they didn't often get
blown seaward over the broad Atlantic. At the end of that time,
however, I observed one morning a pair of finches, after a heavy storm,
drying their poor battered wings upon a shrub in one of the islands.
From this solitary pair a new race sprang up, which developed after a
time, as I imagined they must, into a distinct species. These local
bullfinches now form the only birds peculiar to the islands; and the
reason is one well divined by one of your own great naturalists (to
whom I mean before I end to make the _amende honorable_). In almost
all other cases the birds kept getting reinforced from time to time by
others of their kind blown out to sea accidentally--for only such species
were likely to arrive there--and this kept up the purity of the original
race, by ensuring a cross every now and again with the European
community. But the bullfinches, being the merest casuals, never again
to my knowledge were reinforced from the mainland, and so they have
produced at last a special island type, exactly adapted to the
peculiarities of their new habitat.
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