140 THE ZOOLOGIST. 



The first Terns' nests were batched on June 14th ; and 

 from then on a certain number hatched off weekly, approxi- 

 mately in the order in which I had numbered them, until on 

 July 20th there were only two of their nests left unhatched, the 

 two marked on July 12th. On July 5th several Gulls' nests 

 were either hatched or hatching. On July 20th there were 

 still six of them unhatched. 



My visits, with intervals of a week between them, were too 

 far apart to enable the period of incubation to be fixed accurately. 

 The only thing that can be said is that in neither bird did the 

 period exceed twenty-eight days. The observations pointed 

 rather to the period of close sitting being twenty or twenty-one 

 days after the complete clutch had been laid. In the case 

 of the Black-headed Gulls, in half a dozen instances the period 

 from the first egg of a clutch of three to the chipping of the 

 eggs came within twenty-eight days. 



Out of the fifty-one Terns' nests, there were thirty- six 

 clutches of three eggs, and fifteen clutches of two eggs. Out of 

 the thirty-five Gulls' nests, twenty-five had clutches of three 

 eggs, and nine had clutches of two eggs ; while two nests had a 

 single egg, which eventually turned out to be addled. 



The nests of both species were scattered over a considerable 

 area of ground ; those of the Terns being distributed in a series 

 of loosely connected clumps. That is to say, you would find 

 half a dozen Terns' nests, with ten to fifteen feet separating 

 them ; then a single nest, here and there, at quite distant 

 intervals ; then another small collection quite close together. 

 The Gulls' nests were in and out amongst those of the Terns, 

 sometimes quite close to them and to those of their own species; 

 but for the most part widely separated, and the bulk of them 

 forming a fringe round the outside of the area chiefly affected 

 by the Terns. The whole of the nesting site occupied by the 

 two species spread out to a length of a mile and a half, by a 

 width of half a mile. 



The greater number of the Terns' nests were made amongst 

 the fine grass and thrift. They were open nests, that is, with- 

 out any long vegetation overhanging their margins — with the 

 exception of two which were built in some tufts of purslane with 

 the stems overhanging the eggs, so much so as to suggest a Red- 



