VARYING FECUNDITY IN BIRDS. 25 



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 nume- 

 rous 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 con- 

 spicuous. 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 com- 

 parative 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. 



* Mr. A. K. Wallace has thus modified this statement : — " The Fulmar 

 Petrel exists in myriads at St. Kilda and other haunts of the species, yet it 

 lays only one egg." (' Darwinism,' p. 30). 



