324 BRITISH BIRDS. 



Another group which lays white eggs, in holes in trees 

 and cavities in cliffs, is the Psittaci. All those parrots 

 concerning Avhich I have any information relative to 

 their incubating habits, cover their eggs from the laying 

 of the first. No doubt the habit is common to most or 

 all of the species, for it must be of great value in preserving 

 the white eggs from the unwelcome attentions of egg- 

 seeking animals. 



When last writing on this subject (Vol. IV., pp. 141, 142) 

 I gave examples of the hatching off of clutches of eggs 

 of the Black-headed Gull (L. ridibtindus), shoAving that 

 incubation, in this species, commences as soon as the hen 

 has deposited the first egg. Other species of Larinae in 

 Avhich I have noted the same habit, are the Great Black- 

 backed Gull (L. marimis), the Common Gull (L. canus), 

 and the Lesser Black-backed Gull {L. fusciis). In all 

 probability the habit is common to the whole subfamily. 

 I have noted the same thing in the case of the Arctic 

 yi\ux?\, {S. crejndatus), and have good reason to believe that 

 the Great Skua {M. catarrhactes) does not differ. 



It is interesting to find that Mr. F. M. Chapman, in his 

 Cam'ps and Cruises of an Ornithologist, writing of the 

 Skimmers (Rhynchopinse) on Cobb's Island, says : " The 

 four creamy A\hite eggs are conspicuously marked with 

 black, and are by no means difficult to see." Later he 

 states : " The chicks seem to appear on successive days." 

 No doubt these birds are ovitegous. 



My experience of the Black Guillemot {U. grylle) has 

 been, that incubation begins with the deposition of the 

 first egg. 



A bird which commonly lays its eggs in very exposed 

 situations is the Water-hen (G. chlorojms), and, as might 

 be suspected, this species sits on them constantly. 



The Accipitres are ovitegous. The Egyptian Vulture 

 {N. 2)ercno2)terus) has been recorded as covering her eggs 

 from the time the first is laid. The habit is well known 

 in the case of the Sparrow-Hawk (A. nisus) ; the following 

 is an example of the hatching off of this species : The 



