MISCELLANEOUS NOTES. 223 



from their feeding grounds at sea to roosting quarters on the numerous rocky 

 islets, that stud this stretch, in the teeth of a stiff breeze and over a choppy 

 sea. The formation was invariably in single file, each bird about a length in 

 rear of and in echelon to the lee of the preceding one. The flight was 

 maintained a Eew points off, not directly into the winds' " eye " and just 

 above the water, the troughs and crests of the waves being followed so as to 

 obtain the shelter afforded by the retarded air currents near the surface. 



The distant spectacle of these long strings of brown objects rapidly mov- 

 ing across and appearing and disappearing above and below the surface of the 

 sea made it easy to imagine bow in former and less sophisticated seafaring 

 times the wonderful mariners' yarns of " Monstrous sea serpents careering 

 o'er the Deep " arose. 



Speculation regarding the significance of the echelon formation above 

 referred to raises some interesting questions on bird aviation. Why should 

 this flight formation be usual in flocks of some species and not in others, 

 and how are the former (as they evidently are or the formation would not be 

 employed) aided in their flight by such formation ? 



A little consideration will call to mind those species in flocks of which it is 

 in vogue, e.g., the Cranes, Storks, Geese, Ducks, certain Waders and sea-birds 

 etc. Also flocks in which it is not seen or is not noticeable such as those of 

 the smaller passerine species, the Gulls, Rooks and Lapwings, and in coveys 

 of partridges or packs of grouse, etc. If we bear in mind how species in both 

 of the above categories fly in flocks the suggestion will occur that the forma- 

 tion in question is intimately connected with uniformity and compactness of 

 flocks, with weight and size of the component individuals, with velocity 

 with the powers of sustained flight required by migrant species and with 

 capacity, in spite of size, for making headway in adverse winds. Conversely 

 that it confers no advantage on flocks in which the individuals do not fly in 

 very close proximity to each other, in which the formation is a loose and 

 straggling one, in which the individuals, although fast fliers, have little power 

 of sustained flight, and in those composed of birds whose small size offers 

 comparatively little resistance to the air. 



The answer to the first half of the question must then, I think, lie in the 

 characteristics of the different species of gregarious birds and the necessities of 

 their existence. 



To the second half the answer must, I think, be sought for in the behaviour 

 of the atmosphere on the passage at speed of a heavy body through it. A large 

 or heavy bird in rapid flight in a still or slowly moving atmosphere must 

 continually displace a volume of air equal to its bulk and thus be the cause 

 of a powerful indraught in its immediate rear, Behind the same bird flying 

 against a high wind if there is no indraught there is yet a certain space in 

 which the air is comparatively still. In the former case a bird immediately 

 behind would be in a strong following wind, a state of things birds dislike 

 intensely as it upsets their equilibrium. In the latter the bird would be to 



