HIGH MORTALITY AMONG YOUNG COMMON TERNS 277 



was certainly many times this figure : a very large 

 margin can thus be left for dead marked birds not 

 discovered. The other figures suggest that on 21st 

 July the marked young stood to the total hatched 

 by that date as 4 to 125. As the total marked up to 

 that time was 70, this would represent about 2200 

 young birds in all a very likely figure. The 125 

 and 4, of course, represent only the mortality observ- 

 able on a single date, and give no clue to the total 

 death-rate. In 191 3 Dr Galloway found dead none 

 of the 43 young Terns marked in that season. 



A. L. T. 



Conclusions. 



The young of the Common Tern are subject in certain 

 seasons to an extremely high death-rate, which applies to all 

 ages from the newly hatched to the fully fledged. Most 

 of the dead are not injured in any way, and there is also no 

 ground for suspecting parasites or disease. 



Sand-drifting during high winds buries both eggs and 

 very young birds, but does not explain the hundreds of 

 unburied dead of all ages. 



Long droughts occurred in both the bad seasons here 

 described, but the death-rate continued high after the 

 cessation of drought in 19 10. 



The appearance of the dead suggests starvation, and it 

 seems certain that the food of the young is very restricted 

 in kind, and that the supply is liable to be cut off. For the 

 season 1912 the starvation theory seems all-sufficient; but 

 the 19 10 observations include some contrary evidence, 

 namely, the fact that the almost omnivorous Black-headed 

 Gulls were affected in that season, and that the death-rate 

 among the Terns, also in that year only, varied noticeably 

 with the nature of the ground at different parts of the 

 colony. This latter fact remains unexplained. 



Postscript. Since penning the above the writers have 

 read the following sentences regarding mortality at the 

 Blakeney (Norfolk) " Ternery," where 1912 was a good 



