96 



difficulties they become. It will be necessary to recapitulate a 

 little in examining the feats this poor bird is required to accom- 

 plish. On p. 37 the Northern Bluethroat is cited as a species 

 performing its migrations from its breeding grounds in the north 

 to its winter quarters in the south, in a rigidly-adhered-to, north- 

 to-south hne of flight, and in a broad column whose front corres- 

 ponds to the longitudinal area of the former district. We are also 

 told that Heligoland forms the most western limit of this migra- 

 tion front, and that the Blviethroat only in the rarest instances 

 deviates from the aforesaid direction of flight. In spring the 

 migration is conducted in a similar manner, but the direction of 

 the flight is of course reversed. At this period of the year, if 

 the weather be fine and warm, the bird is an abundant visitor 

 to Heligoland. May 26th, 1880, is a date pointed out when 

 this was especially the case. On this occasion — " all the gardens 

 of the island teemed with them to such an extent that their 

 numbers in the nearest gardens were adjudged above five 

 hundred." This gives a good idea of the numbers of Bluethroats 

 migrating by this particular fly-line. It is further stated (p. 265) 

 that during its spring passage from Central and Northern Africa to 

 the north of Scandinavia, in the absence of cold and dry northerly 

 winds at the end of May and April, it appears on Heligoland as 

 a daily visitor, and if, in addition, the weather be fine and warm 

 with a light south-east wind, it frequently occurs on days of this 

 kind in such large numbers that as many as from thirty to fifty 

 males have been obtained. The migration thus lasts one month. 



We also read that the Northern Bluethroat travels only during 

 the night, setting out at dusk and ending its journey at daybreak, 

 or immediately after sunrise. Hence, being unobserved in inter- 

 mediate localities, it accomplishes a flight of more than 1,600 

 geographical miles from Egypt to Heligoland in the course of a 

 spring night of scarcely nine hours, giving the almost miraculous 

 velocity of 180 geographical miles per hour. The further fact 

 that this liird is never seen during the night by the lantern of the 

 lighthouse is cited as an additional proof that the long migration 

 from Northern Africa is performed in one uninterrupted flight 

 (p. 45). It will be noted that the flight is first stated to travel 

 between Central Africa and the north of Scandinavia, but in 



