26 DARWINISM chap. 



two or more broods a year, ten will be below the average of 

 the year's increase. Such birds as these often live from fifteen 

 to twenty years in confinement, and we cannot suppose them to 

 live shorter lives in a state of nature, if unmolested ; but to 

 avoid j^ossible exaggeration we will take only ten years as the 

 average duration of their lives. Now, if we start with a single 

 pair, and these are allowed to live and breed, unmolested, till 

 they die at the end of ten years, — as they might do if turned 

 loose into a good-sized island with ample vegetable and insect 

 food, but no other competing or destructive birds or quadrupeds 

 — their luimbers would amount to more than twenty millions. 

 But we know very w^ell that our bird population is no greater, 

 on the average, now than it was ten years ago. Year by year 

 it may fluctuate a little according as the winters are more 

 or less severe, or from other causes, but on the whole there is 

 no increase. What, then, becomes of the enormous surplus 

 population annually produced? It is evident they must 

 all die or be killed, somehow ; and as the increase is, on the 

 average, about five to one, it follows that, if the average 

 number of birds of all kinds in our islands is taken at ten 

 millions — and this is probably far under the mark — then about 

 fifty millions of birds, including eggs as possible birds, must 

 annually die or be destroyed. Yet we see nothing, or almost 

 nothing, of this tremendous slaughter of the innocents going 

 on all around us. In severe winters a few birds are found 

 dead, and a few feathers or mangled remains show us where 

 a wood-pigeon or some other bird has been destroyed by a 

 hawk, but no one would imagine that five times as many birds 

 as the total number in the country in early spring die every 

 year. No doubt a considerable proportion of these do not die 

 here but during or after migration to other countries, but others 

 which are bred in distant countries come here, and thus 

 l)alance the account. Again, as the average number of young 

 jjroduced is four or five times that of the parents, we ought to 

 have at least five times as many birds in the country at the 

 end of summer as at the Ijeginning, and there is certainly 

 no such enormous disproportion as this. The fact is, that the 

 destruction commences, and is probably most severe, with 

 nestling birds, which are often killed by heavy rains or blown 

 away by severe storms, or left to die of hunger if either of 



