64 CHARLES DARWIN 



Many theories, even phrenological theories, have been ad- 

 vanced to explain the origin of the cuckoo laying its eggs in 

 other birds' nests. M. Prevost alone, I think, has thrown 

 light by his observations 9 on this puzzle: he finds that the 

 female cuckoo, which, according to most observers, lays at 

 least from four to six eggs, must pair with the male each time 

 after laying only one or two eggs. Now, if the cuckoo was 

 obliged to sit on her own eggs, she would either have to sit 

 on all together, and therefore leave those first laid so long, 

 that they probably would become addled; or she would have 

 to hatch separately each egg, or two eggs, as soon as laid : 

 but as the cuckoo stays a shorter time in this country than 

 any other migratory bird, she certainly would not have time 

 enough for the successive hatchings. Hence we can perceive 

 in the fact of the cuckoo pairing several times, and laying 

 her eggs at intervals, the cause of her depositing her eggs 

 in other birds' nests, and leaving them to the care of foster- 

 parents. I am strongly inclined to believe that this view is 

 correct, from having been independently led (as we shall 

 hereafter see) to an analogous conclusion with regard to 

 the South American ostrich, the females of which are 

 parasitical, if I may so express it, on each other; each 

 female laying several eggs in the nests of several other 

 females, and the male ostrich undertaking all the cares 

 of incubation, like the strange foster-parents with the 

 cuckoo. 



I will mention only two other birds, which are very com- 

 mon, and render themselves prominent from their habits. 

 The Saurophagus sulphuratus is typical of the great Ameri- 

 can tribe of tyrant-flycatchers. In its structure it closely 

 approaches the true shrikes, but in its habits may be com- 

 pared to many birds. I have frequently observed it, hunting 

 a field, hovering over one spot like a hawk, and then pro- 

 ceeding on to another. When seen thus suspended in the air, 

 it might very readily at a short distance be mistaken for one 

 of the Rapacious order; its stoop, however, is very inferior 

 in force and rapidity to that of a hawk. At other times 

 the Saurophagus haunts the neighbourhood of water, and 

 there, like a kingfisher, remaining stationary, it catches any 



Read before the Academy of Sciences in Paris. L'Institut, 1834, p. 418. 



