( 105 ) 

 ON INCUBATION. 



BY 



ERIC B. DUNLOP. 



As has previously been shown,* many birds belonging 

 to various Orders commence incubation upon the laying 

 of the first egg. This habit is undoubtedly of the 

 utmost value to many species, saving the eggs from 

 destruction by the numerous animals which devour 

 them with avidity : in fact it does not seem too much 

 to say in the case of some, that if the eggs were left 

 exposed, such would be the attacks made upon them, 

 that extinction would shortly result. 



If further investigation be made, however, the fact 

 is revealed that the habit is not an unmixed blessing, 

 but brings in its train a great mortahty amongst the 

 young of various ovitegous birds of widely different 

 Orders. That the mortality referred to should be 

 directly attributable to a habit which is essentially 

 protective, is a very remarkable fact, but one which 

 can, I think, be clearly proved. 



Few people as they pass beneath a rookery would 

 imagine that a tragedy occurred in practically every 

 nest built by these birds : on the contrary the sight 

 and sound of Rooks at home during the nesting-period 

 calls to our minds all that is commonplace and normal. 

 To associate the homely Rook with the tragic, seems 

 to be impossible : nevertheless, according to my observa- 

 tions, the seemingly impossible must be admitted to 

 the realm of fact. As is well known, the Rook very 

 frequently deposits five eggs and occasionally six. It 

 would appear, on the face of it, that the parents should 

 not unusually bring five young birds up to the age 

 at which they are ready to leave the nest. In point of 

 fact, that is rarely or never accomplished. The Rook 

 does not usually rear more than three young, and 

 frequently does not attain even to that moderate degree 

 of success. 



* See Vol. v., pp. 322-27, and Vol. IV., pp. 137-45. 



