322 Capt. C. lugraiiQ on the [Ibis, 



weather) they will show a tendency to travel low — so low, 

 in fact, that sometimes they almost skim the surface of the 

 sea, as the writer has himself observed off the China coast. 



In clear weather, on the other hand, the majority of birds 

 will fly so high that even the largest of the day migrants 

 passes unseen on its way to and from its summer quarters. 

 Some species, however, appear to fly low habitually. 

 Writing of the diurnal migration as noticed at the Tuskar 

 Rock, Ireland, Prof. C. J. Patten estimates the average 

 height for Meadow-Pipits to be 70 ft., for Wagtails 120 ft., 

 and for Swallows 40 ft. 



During the two years I was with the R.F.C. and Royal Air 

 Force in France (1916-1918) I made every effort to collect 

 information that would throw some light on the subject under 

 discussion, and with this object in view I interrogated a very 

 large number of pilots and observers — possibly as many as 

 seven to eight hundred. The majority of these had seen no 

 birds above a few hundred feet, but a small percentage had 

 done so and were able to impart very interesting information, 

 most of which I have endeavoured to incorporate in the 

 present paper. Vague statements, or those open to question, 

 have been omitted. 



I have heard it said that the average man is too unobservant 

 to make a mental note of birds encountered during the course 

 of a flight. Under ordinary conditions there might be some 

 ground for this argument, but it cannot apply in the present 

 case. W^hile on a patrol over the enemy's lines, vigilance 

 was always of such vital importance that a pilot was extremely 

 unlikely to overlook the passing of a flight of birds, and, 

 moreover, an encounter of this kind was always regarded as 

 an interesting event and one sufficiently unusual to warrant 

 comment on return to the squadron, and generally an entry 

 in the observer's diary. 



For these reasons 1 think the data obtained can be regarded 

 as tolerably reliable with regard to heights, dates, etc. ; but 

 unfortunately, as the majority of the observations weie 

 communicated by men making no pretentions to ornitho- 

 logical knowledge, the identification of the species, and 

 sometimes the family, was not always certain. 



