176 STUDIES IN BIRD-MIGRATION 



the rays and striking against the lantern until 2 a.m., when, 

 owing to the appearance of fog, the dismal and terrifying 

 blasts from the fog-horn were turned on. These soon 

 scared the visitors, and saved them from the mystifying 

 and dangerous influence of the brilliant beams of light. 

 Herons, Wheatears, and White Wagtails were also 

 present, the weather being favourable for the display of 

 the decoying powers of the lantern. On the two following 

 days a number of Terns, whose identity could not be 

 determined, were present off the south end of the island 

 — the only instance of the presence of these birds during 

 the daytime that has come under my notice. On the night 

 of the 20th, at 9 P.M., a party of Terns on migration again 

 appeared in the vicinity of the lighthouse, but as the 

 night was clear they did not approach the lantern, and 

 only announced their presence by their cries. This, and 

 much other evidence in my possession, proves that Terns 

 largely migrate during the hours of darkness. 



The Common Tern has only during recent years been 

 added to the list of the breeding birds found in Shetland. 

 The above is the only instance in which this species has 

 been identified as a visitor to Fair Isle. 



Sterna macrura, Arctic Tern. — Our introduction to 

 this species as a Fair Isle bird has just been related 

 under the Common Tern. On 22nd September 1909, a 

 number noisily announced their appearance at 7.30 p.m. 

 and flew in the rays of the lantern for a short time. On 

 the following night a party arrived at 9.45 p.m., but did 

 not remain long. 



Terns on migration chiefly visit the Isle during the 

 night-time and mostly pass unnoticed unless the weather 

 conditions be such as to render the rays from the lantern 

 conspicuous. No doubt these birds are to be seen at 



