( 109 ) 



ON INCUBATION.* 



An Observational and Experimental Proof of the 

 Value of the Ovitegous Habit in Birds. 



BY 



ERIC B. DUNLOP. 



As the best means of ascertaining tlie value of the 

 o\'itegous habit to birds, I devoted some time during 

 the breeding-season to watching the Herring-Gull {L. 

 argentatus), which I had previously found normally 

 incubated from the laying of the first egg. Various 

 experiments were also made. All these observations and 

 experiments are not given in the following pages, but 

 sufficient evidence is brought forward to make. I beheve. 

 the value of the ovitegous habit undeniable. 



On May 8th the first eggs of the Herrmg-Gull were 

 noted, two nests containing single eggs : the breedmg-place 

 was on a small island. One of the nests was in full vie\\ 

 of a blind which had been previously erected ; soon after 

 I had entered the blind and the boat had left, one of the 

 birds belonging to this nest settled and stood about ten 

 feet from it. An American Crow (C. brachyrhynchos) 

 shortly after settled in a near-by tree and made a sudden 

 swoop down towards the nest : the Gull rushed forward 

 with upraised wings and drove him off, the Gull's mate 

 coming up and assisting. After a while the Crow returned 

 and flew past ; the Gull ran forward as fast as it could and 

 sat down on the nest and egg (it had retired a few feet 

 from the nest and stood there after the first raid). The 

 bird now incubated for a while and then returned to its 

 former stand. Again the Crow flew near, and yet again 

 the Gull ran forward and covered the egg. The Crow- 

 settled in front of the nest and the black one's mate 

 also came up and settled beliind. The Gull was very 

 uneasy, calling continually ; a raid on the egg was no 



* For previous articles on this subject see Vol. IV., pp. 137-4."). 

 Vol. v., pp. 322-27, Vol. VII., pp. 10.->-l4. 



