Page:The Zoologist, 4th series, vol 3 (1899).djvu/49

Rh of the parents, and certainly by the covering capabilities of the sitting hen. Mr. Davies allows that the food-supply may affect the parents, for he says that the number of eggs is often less when insect food is not abundant. And, again, he gives as a reason for the two broods of Finches, &c, that "it is necessary for them to produce eight or ten of their kind in a season to aid in killing off from the cultivated lands the vast swarms of insects to which the summer has given birth;" which means that where the supply of insects is great there will be plenty of birds to prey upon them. But this ought to apply equally to the Warblers, &c.

Mr. Davies proceeds to give reasons why in one family of birds the usual number of eggs laid by the species of that family is large; whereas in another family the reverse is true. With regard to Game Birds, he suggests that the large number of eggs is to meet a large amount of destruction. It seems to me that not only with Game Birds, but with all birds, this is the secret of a larger or smaller number of eggs. Darwin wrote: "The Fulmar Petrel lays but one egg, yet it is believed to be the most numerous bird in the world" ('Origin,' p. 52). And I should suppose that the causes which controlled the average numbers of eggs of different species were—(1) the supply of food; (2) the number of enemies; (3) the power of self-defence or escape.

It is not possible to accept some of Mr. Davies' reasons. For instance, he supposes that the Nightjar lays two eggs, because several gaping young birds would be a conspicuous object. As they only gape after dusk, no number of them would be conspicuous. I know no object less conspicuous than a Nightjar covering its young or eggs.

Again, is not the reason for the single egg of the Guillemot to be looked for in the special defences of this bird rather than in the shape of the egg? No doubt this shape is a protection. If Guillemots' eggs were shaped like those of most birds, very few would be hatched. But the one egg is laid in a place of comparative safety, and the bird itself is quick on the wing and an apt diver, and for part of the year lives far from land, and so is probably less subject than most birds to attacks of foes.