246 THE ZOOLOGIST. 



matter might be worked out theoretically, and I arranged a sort 

 of time-table, giving the speeds of a stream of birds an hour 

 apart, crossing a series of concentric eddies moving at known 

 velocities in a given direction. The actual courses, as worked 

 out for me by Mr. H. G. Taylor, M.Sc, A.M.I.C.E., prove con- 

 clusively that a "migration route," either for a species or for a 

 general tide of birds, is a physical impossibility. Mr. T. A. 

 Coward, in his tiny yet most valuable book, ' The Migration of 

 Birds,' has figured a route modified from one of Mr. Taylor's 

 charts, and I hope soon to see the publication of a set of these 

 significant diagrams, with the data on which they are based. 



Perhaps those who do not readily understand how a flying 

 bird cannot possibly have its feathers ruffled by the wind — and I 

 admit that the reasoning is not so simple as some would have 

 us believe — may be contented with the account of a simple 

 experiment that can be repeated as often as desired. In places 

 where Gulls are in the habit of being fed it is easy to persuade 

 any individual bird to move in a circle. Choose a bird and toss 

 it a fragment of fish ; then, as the same individual flies past 

 again throw it another ; in a short time it will make its circles 

 as small as possible, in order to lessen the intervals between the 

 morsels of food (in the Black-headed Gull the minimum circle 

 is about thirty to thirty-five feet in still weather). On a windy 

 day watch the plumage carefully, especially during that part of 

 its course when the bird is tail to wind — there ivill be no ruffling 

 in any way. Observe, however, that as the Gull is about to 

 alight, when flight has ceased and the force of gravity acts as a 

 sort of connection with the earth, the feathers are often ruffled, 

 although the bird is in the air. 



It should now be clear that birds cannot cover long distances 

 against a wind ; that they can, and regularly do, fly with the 

 wind, and this without any ruffling of plumage, and without loss 

 of lifting power ; and I would go further, and express my belief 

 that the migrations of birds are aided to a very great extent by 

 the movements of the atmosphere. Every field ornithologist 

 must be familiar with the intelligent manner in which birds 

 habitually make use of local currents or eddies of air or water, 

 either in play or when about their more serious affairs : a Swan 

 using its wings as sails ; Gulls utilizing the upward current 



