1 91 9.] Height at ivhich Birds migrate. 325 



wings at a similar height seen Marcli ]917 (Lt. O. B.Wills, 

 .34 Squadron). 



My second highest record is of some "Sandpipers" 

 observed by ('apt. E. Pope, 57 Squadron, over Arras 

 towards the end of March 1917. These birds, '-'about the 

 size of a Snipe," were flying eastwards at an elevation of 

 12,000 ft. 



Other birds, somewhat doubtfully identified but which 

 were very probably Limicoline species, were seen by 

 Major Russell of 32 Squadron at 10,000 ft., and by 

 Lieut. King of 43 Squadron at 9500 ft., the latter on 

 18 December flying in a southerly direction. 



Early in March 1918 Col. Portal saw a party of what 

 I imagine to have been Whimbrel, since he describes them 

 as beinu' " exact! v like Curlews, oiilv about two-thirds their 

 size."^ These were at 4000 ft., travelling very fast over 

 Lens in a north-easterly direction. 



Herons have been met with by Lieut. O. B. Wills at 

 3000 ft., and by Capt. S. Stammers between 2500 ft. and 

 3000 ft. The latter, a single bird flying in a north-westerly 

 direction, was over the Crouch, Essex, in September 1916. 



In fine, still weather birds will often ascend to con- 

 siderable heights for apparently no other reason than mere 

 joie de vivre. During the mid-summer months, towards 

 the heat of the day, Swifts, and possibly to a lesser extent 

 some of the Swallows, make a practice of rising to the 

 cooler strata of air, and I have often met with Apus apus 

 in the mountains at several thousand feet, while in Trinidad 

 I have noticed that the local forms of Swifts regularly dis- 

 appeared from the lower levels as the sun gained force. 



The four records I have of Swifts or Swallows (my 

 informants were not able to differentiate between these 

 species) at heights varying from 2500 ft. to 3000 ft. were 

 probably attributable to this habit rather than to migratory 

 movements. The same may also be said of the Gulls met 

 with by Major Leather (88 Squadron) at 3500 ft. in 

 Scotland during the spring of 1917, and of- the large 

 numbers of Wood-Pigeons seen by Col. Portal '' circling 

 round " at 1500 ft. 



