HIGH MORTALITY AMONG YOUNG COMMON TERNS 271 



NOTES ON HIGH MORTALITY AMONG YOUNG 

 COMMON TERNS IN CERTAIN SEASONS. 



By A. Rudolf Galloway, M.A., M.B., CM., and A. Landsborough 

 Thomson, M.A., B.Sc, M.B.O.U. 



The writers of the following notes wish to draw attention 

 to the extraordinarily high " infant mortality " that prevails 

 in certain seasons in some nesting colonies of the Common 

 Tern {Sterna hirundo L.). The colony to which their observa- 

 tions relate is one of over a thousand nests, situated on the 

 extensive sands of Forvie, on the Aberdeenshire coast, 

 immediately to the north of the estuary of the Ythan. The 

 seasons in which the high mortality was evident were 1910 

 and 191 2, and the notes for these years are given separately 

 below. Other seasons of which the writers are able to speak 

 are 1907, 1908, 1909, 191 1, 191 3, and 1914, although only 

 as regards the earlier part of the first two : in all these years 

 nothing more than the normal slight or moderate mortality 

 was recorded, except during a short period in the otherwise 

 favourable summer of 1914, a point which will receive further 

 mention. The two bad seasons stand out in strong contrast 

 to the others by reason of the excessive rate of mortality 

 which then prevailed ; on numerous occasions the ground 

 was strewed with many hundreds of dead and dying young, 

 and the total number which survived to take wing in these 

 years must have been pitifully small. Similar occurrences 

 have been reported from colonies in other parts of the 

 British Isles, and, as there is room for doubt as to the cause 

 or causes, the matter seems to be of considerable interest. 



The High Mortality at Forvie in 191 o. 



Unfortunately I saw only the early phases of the high 

 mortality in both 19 10 and 191 2, owing to absence from 

 Aberdeenshire after the middle of July. For the following 

 observations regarding the former season I am, therefore, 



