( 322 ) 

 ON INCUBATION. 



BY 



ERIC B. DUNLOP. 



In a previous article on this subject (Vol. IV., pp. 137- 

 145), I showed that there is a considerable number of 

 birds which commence to incubate as soon as the first 

 egg has been deposited. The birds which have this habit 

 it will be convenient to term the Ovitegse ; the species 

 which do not sit until the full clutch has been laid, the 

 Ovinudse. In this paper I shall show hoAv extensive 

 is the former group. Writing of the Kaven (C. corax) 

 in my last paper, it was suggested that many eggs of 

 this species Avould be rendered infertile by the elements, 

 if the bird did not sit from the first. Further experience 

 of these birds proves that incubation does begin with 

 the deposition of the first egg. The habit is not only 

 of value to the species in saving the eggs from the effect 

 of frost and snow, but also by protecting them from egg- 

 stealing birds. This was proved in an unusual manner : 

 A pair of Ravens having been disturbed at their nest by 

 a keeper, forsook it ; very shortly afterwards the nest 

 was raided by Crows ; search revealed the eggs, which 

 had been sucked, on an adjacent hill-end. 



In my previous paper, I stated that the Magpie (P. 

 rustica) exceptionally covers her eggs from the time the 

 first is laid, but this species undoubtedly belongs to the 

 Ovitegse. Building of the large nest commonly begins 

 in March, and the trees being then leafless, it is a prominent 

 object, frequently being visible at a distance of fully a 

 mile. Great risk is run thereby from the depredations 

 of egg-sucking animals. If the bird was not constantly 

 present to protect her eggs, it is probable that few Avould 

 be left to hatch. 



The Carrion-Crow [C. corone) also commonly sits as 

 soon as egg-la3dng has commenced and, no doubt, the 

 same is the case with the Hooded Crow (C. comix). 



