Jones — On Common and Roseate Terns. 39 



themselves to the different environment which these places 

 afford. 



The eggs are generally deposited on successive days, rarely 

 a whole day intervening between the deposition of two eggs. 

 Incubation begins when the first egg is deposited, and the eggs 

 hatch in the order in which they were deposited. The period 

 of incubation for six nests studied was 21 days, or the same 

 as for the domestic fowl. 



Both male and female take regular turns sitting, but my ob- 

 servations indicate that the female spends more time on the 

 nest than the male. In the cases studied, a bird later found 

 to be the female, approached the nest abruptly and settled upon 

 the eggs without any preliminaries. She remained quiet 40 

 minutes, when she uttered a peculiar call which was repeated 

 at short intervals until a bird separated itself from the hover- 

 ing cloud, or company at the water's edge, when she stood up, 

 took a few steps, and flew away. The male alighted on the 

 sand several rods to leeward of the nest and approached it 

 gradually, simulated feeding, and called loudly at intervals. 

 \^■hcn he reached the nest he merely stood over the eggs to 

 protect them from the scorching rays of the sun, and kept 

 calling at intervals. In 20 minutes he became more restless, 

 called more frequently, and soon ran some distance to wind- 

 ward of the nest and took wing. Within a few minutes the 

 female alighted on the sand near the nest and went abruptly 

 to it and settled upon the eggs. This maneuver was repeated 

 many times, with slight modifications. Upon the slightest 

 disturbance the birds leave the nest and circle about overhead, 

 calling excitedly and loudly, often making sallies at the head 

 of the intruder. At first it seemed impossible to select the 

 parents from the other scolding birds which constantly hovered 

 over me, and since one can seldom find a nest which is suffi- 

 cienitly isolated to enable one to concentrate attention upon it 

 alone, there might well be confusion as to the owners of any 

 given nest. But with the young the case is more definite. 

 When a young bird is picked up, two of the hovering birds 

 becnir.e much bolder than the rest, dashing within a few feet 

 of the intruder. After considerable careful studv it became 



