244 THE ZOOLOGIST. 



Great numbers of birds were sheltering in the hollow ditches, 

 and when I struck one of these the inmates were forced to take 

 wing. A single example will suffice here. 



Walking up wind to a ditch, I came upon a small party of 

 Hooded Crows, and on my approach these tried to fly away from 

 me, in the teeth of the blizzard. Flying at what was obviously 

 their full speed, they made no headway whatever, and, indeed, 

 even moved very slowly towards me ; had I been free from the 

 wind myself, I could easily have touched one of them with my 

 walking-stick, and thus they hung for a second or so in the air 

 before me. Finding their efforts useless in that direction, the 

 birds promptly turned tail, and swept past me down wind. I 

 turned also, and saw them rise high in the air to clear a group 

 of tall trees a quarter of a mile inland. 



Let us assume for the moment that the wind was exactly fifty 

 miles per hour, or, as an alternative, that the speed of the Crow 

 is fifty miles per hour. Flying head to wind, as we have seen, 

 their velocity in relation to the earth was 50 — 50 = miles per 

 hour, but in the opposite direction it must have been 50 + 50 = 

 100 miles per hour over the surface of the earth. Since then I 

 have made many similar observations (but never under such 

 terrible conditions !). No longer ago than May 12th last, sitting 

 in the shelter of a rock at the summit of one of the Peak hills, I 

 saw a Titlark flying head to wind, and moving tail foremost past 

 my shelter at an estimated speed of two miles an hour. Assuming 

 that its usual velocity was 30, the wind must have been 32, and 

 when the bird turned (as it did do) its net speed between points 

 on the earth's surface was 30 + 32 = 62 miles per hour. If 

 we use these figures in conjunction with the "Head Wind Theory" 

 of migration, we shall see that such a bird as a Titlark could 

 not cross the North Sea in less than 150 hours, unless the 

 so-called "favouring" wind kept below 28 miles per hour; 

 but if we drop this theory and admit that a bird actually can fly 

 tail to wind, we shall see that with a 30-mile breeze a Titlark 

 could cross the North Sea in five hours. I cannot say that 

 I quite follow Mr. W. Eagle Clarke in his interesting and 

 epochal work, ' Studies in Bird Migration.' As I understand 

 his remarks, he does not now insist on the acceptance of his 

 " head wind" views described in the Beport of the British Asso- 



