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Show 26 DARWINISM CHAP. two or more broods a, year, ton will be below. tho avomgo of tho year's increase. Such birds as those often hve from fifteen to twenty years in confinement, and we c.annot suppose them to live horter lives in a state of nature, 1f unmolested ; but to avoid possible exaggeration we will tak? only ton Y?ars a~ the avoraae duration of their lives. Now, If we start with a smgle pair, ~nd these arc allowed to live and breed,. unmol~stcd, till they dio at the end of ten ycars,-as they m1ght do 1f t~rn ed loose into a aood-sized island with ample vegetable and msect food, but no ~ther competing or destructive birds or quad~·upcds -their numbers would amount to more than twenty m1lhons. But we know very well that our bird population is no greater, on the averaac now than it was ten years ago. Y car by year b' h . it may fluctuate a little according as t e wmtcrs iU'C m OI~e or less severe, or from other causes, but on the whole there 1s no increase. What, then, becomes of the enormous smplus population annually producccl1 It is e.viJont t~cy must all die or be killed, somehow; and as the mcrcasc 1s, on the average, about five to one, it fo1lows that, if the average number of birds of all kinds in our islands is taken iLt ten millions-and this i. prob~Lbly far under the mark- then iLhont fifty millions of birds, including eggs as possible birds, mu~ t annually die or be destroyed. Y ct we see nothing, or almost nothing, of this tremendous slaughter of the innocents going on all around us. In severe winters a few birds arc found dead, and a few feathers or mangled remains show us where a wood-pigeon or some other bird has been destroyed hy a. hawk, but no one would imagine that five times as many hin1s as the total number in the country in early spring die every year. No doubt a considerable proportion of th~so do not die here but during or after migration to other countries, but ot h er~ which are bred in distant countries come here, and tlut :-> balance the account. Again, as the average number of yotLng produced is four or five times that of the parent, we ought to have a,t least five times as IDitny birds in the country iLL Lhe end of summer as at the beginning, and there is corttLin ly no such enormous disproportion as this. The fact is, that the destruction commences, and is probably most severe, with nestling birds, which itrc often killed by heavy rains or blown away by severe storms, or left to die of hunger if either of JJ THE STRUGGLE FOR EXISTENCE 27 t. hek dp arent.s is kildle d ; wh. ile they offer a defenceless pr,e y t o Jac. aws, Jays, an. magpws, and not a few arc ejected from thmr nests by thmr foster-brothers the cucl\·.o os . A s soon as they are fledged and begin to leave the nest great numbers are dcstr?ycd ?Y bu~zards, sparrow-hawks, and shrikes. Of those whiCh migrate m autu~n a considerable proportion arc probably lost at sea ?r othcnVIsc. destroyed before they reach a pl~ce of safety; while thos~ whiCh. remain with us arc greatly thmned by cold and starvatiOn durma severe winters Ex tl h h. . o . . ac y t e same t mg goes on With every species of wild animal and plant. from the lowe t to the highest. All breed at such a rate, that m a fe': years the progeny of any one species would, if allowed t~ mcrcasc unchecked, alone monopolise the land . but a!l ahke arc kept within bounds by various dcstructiv~ agenc~es, so that, though the. numbers of each may fluctuate, they can never l?crmanently mcrcase except at the expense of some others, whiCh must proportionately decrease. Cases showing the Great Powers of Increase of Animals. As the facts now stated are the very foundation of the theory we are considering, and the enormous increase and perpetual dcs~ruction ~ontinually going on require to be kept eve: present m tho mmd, some direct evidence of actual ca. cs of ~ncrease must be ad.duced. That even the larger animals, w~ICh breed comparatively sl.o~Iy, ~ncrcaso enormously when placed unde~ favourable cond1t10ns m new countries, is shown by the rapid spread of cattle and horses in Amcri ·a Colu~bus, in his second voyage, left a few black catUe at S<t: Dommgo, and these ran wild and increased so much thitt, twonty-sevcn years afterwards, herds of from 4000 to 000 head w.er~ not uncommon. Cattle were afterwards taken ~rom this I~land to Mexico and to other parts of America, and I~l 1~87, Sixty-five years after the conquest of Mexico, the Rpamard~ exported ?4, 350 ~id?s from that country and 35,444 f1o~ St. Do~mgo, an mdiCation of the vast llUntbers of these ammals whiCh must then have existed there since those captured and killed could have been only a small ~ortion of the whole. In the pampas of Buenos Ayres there were, at the end. ~f the last century, about twelve million cows and three m1lhon hor·ses, besides great numbers in all other parts |
