326 BRITISH BIRDS. 



April, and occasionally in March, also not infrequently 

 Ravens nest in the vicinity ; early eggs are undoubtedly 

 saved from the effects of frost and snow by the habit, 

 and all from the attacks of the Corvidse. The variation 

 in the size of the young, produced by their difference 

 in age, has sometimes wrongly been attributed to 

 sex. 



The Merlin {F. cesalon) also covers its eggs as soon as 

 laid. The following are the data from a nest I watched : 

 May 3rd, one egg ; May 4th, two eggs ; May 5th, three 

 eggs ; May 6th, three eggs ; May 7th, four eggs. On 

 the 4th the cock bird was sitting. It is certain that in 

 many species the male assists in incubation before the 

 clutch has been completed. 



The Osprey (P. haliaetus) has been recorded as sitting 

 with the first egg. 



In the Ciconiiformes all those species respecting whose 

 nesting habits I have information, belong to the Ovitegse. 



The Cormorant (P. carho) and the Shag (P. graculus), 

 though the latter often nests in recesses, would soon cease 

 to exist if their light-coloured eggs were exposed for any 

 length of time to the attacks of the more agile gulls. 

 Mr. F. M. Chapman records that the young of Darters 

 (Plotus) vary in age in the same nest, and the same is 

 noted of the Boobies (Sula leucogastra). 



The Common Heron (A. cinerea), as previously recorded, 

 incubates as soon as the first egg has been deposited, 

 and undoubtedly so also does the Purple Heron (A. 

 purpurea) and the Great White Heron (A. alba). 



In an article on the Bittern (B. stellaris), (Vol. L, pp. 329- 

 334), Mr. E. W. Wade gives a photograph of a nest 

 belonging to this species, and underneath it notes that 

 the nest was visible at thirty paces when the old bird 

 was not sitting. He further notes that some of the eggs 

 in each clutch are more incubated than others, and the 

 young are of unequal size. The Harriers would certainly 

 profit b}^ the absence of this, and allied species, if they 

 left their nests uncovered. 



