XVI 



above the earth, at which height they are able to distinguish the prominent features of the 

 landscape, such as coast-lines, the principal watercourses, mountain-chains, &c. They usually 

 migrate during clear weather, when they can discern the landmarks on the earth below them — 

 supposing that they are to some extent guided by landmarks ; and if this is the case the 

 bewilderment they exhibit when thick weather sets in is explained by the fact that, their land- 

 marks being obscured, they are at a loss to know what course to pursue, and consequently 

 descend to the nearest resting-place on the earth. At the same time I must add that, it 

 appears to me, the hypothesis that birds are guided by landmarks below them is not confirmed 

 by more recent observations. Mr. Scott made his observations when looking at a number of 

 objects through the nine-inch equatorial at the astronomical observatory at Prince Town, New 

 Jersey, in October 1880, when, the night being clear, he could see the birds passing across the 

 field of observation clearly defined against the bright background. 



The above statement as regards the altitude at which birds travel has been corroborated by 



Mr. Gatke, who has come to the same conclusion from careful observations made on Heligoland 



during nearly forty years. I lately spent a week on Heligoland, and was astonished to see the 



mass of information on the subject he has collected, and which will ere long be published in a 



work he is on the eve of issuing, which will be a most valuable essay on the difficult and so little 



understood subject of migration. He believes, and (as far as I could judge by a glance through 



his rough notes) on excellent grounds, that birds migrate at an altitude of from one (at least) to 



two miles above the earth, and that they travel at a speed far above what has hitherto been 



surmised — the heavy Hooded Crow even attaining a speed of fully twenty-seven geographical 



miles per hour, and many other species travelling at a much greater speed. He surmises that the 



Eed-spotted Bluethroat (Cyanecula suecica) passes from North Africa to Heligoland in a single 



night, which gives a rate of locomotion of about forty geographical miles per hour, a speed which 



he believes may easily be attained at altitudes where the air, being so rarefied, offers, comparatively 



speaking, so little resistance; and it is certainly true that the first point north of its winter 



quarters where this bird is found in considerable numbers is Heligoland. In a letter to Professor 



Baird, of which he gave me a copy, he makes some interesting remarks on the subject of 



migration, which I may transcribe as follows, especially as he is strongly of opinion that birds 



are not in the least influenced by the contour of the countries over which they pass in the choice 



of the direction they take. He says : — " That the direction of the course of wandering birds should 



be influenced by river-courses or mountain-chains is a point which I do not agree to, at least so 



far as Europe comes under contemplation. Here during the fall the route of miscellaneous 



species is so varied that the two principal hosts cross each other at right angles, one great mass 



progressing due west from the furthest east of Asia (e. g. Anthus richardi, Sylvia swperciliosa) 



and continue their course to Heligoland, England, France, and Spain. Besides these, all the 



rare autumnal visitors come here from the far east of Asia, which proves that there must be 



with birds of these regions a strong inherent tendency to a western migration, even in species 



