83 BRITISH BIEDS. 



hindered and turned by unsuitable ground, which acts as does the sea. We 

 know that the Great Sahara desert is such a barrier to the Sylviidce ; and 

 the mountains and rough ground of Wales in the same manner form boun- 

 daries. 



Mr. Blyth appears to attribute a northern and southern knowledge to the 

 Nightingale (^vicle Thompson's ' Birds of Ireland,' vol. i. p. 426, note ; Yarrell, 

 ed. 4, p. 318). If this knowledge exist, it may arise from the double system of 

 respiration in birds, more developed in some than others. Dr. Jerdon says : — 

 " In the Hornbills the very phalanges of the toes are hollow and communicate 

 with the lungs. A high and rapid aeration of the blood is thus maintained ; 

 and the great energy and irritability of the muscular system of birds is a direct 

 consequence of this amount of respiration." Query, true of the phalanges .'' 



Atmospheric influence has certainly considerable effect : one constantly 

 sees that. In my flock of Gulls their motions correspond exactly to the 

 weather-cock over their heads ; they point more truly to the wind. On some 

 days every bird is sitting dow^n, as sheep and horned stock may be observed to 

 repose, each individual being on the ground. Shepherds will tell that some- 

 times a sort of jumping fit runs through the whole flock, and their antics are 

 very pretty. This is atmospheric. 



The above remarks do not apply to old Nightingales ; they know their 

 w^ay. I have taken the most difficult case, that of the young bird without 

 a guide, who does not moult his primaries. 



Thus we see how he finds his way ; his right path in England is south, and 

 to it he must come. The difference between him and the old birds of expe- 

 rience and strong flight may be observed by the eye of one accustomed to 

 watch migration, in Larks particularly : the veterans travel with such a 

 determined shoot forward. 



Why do some go and some stay, as among Larks and Goldfinches in 

 England, and (as stated by Darwin)the Mocking Thrushes (^Mimus polyghttus) 

 in Louisiana, of which some are harbour birds and the rest migrate to the 

 Eastern States ? To understand this w^e must look a little into their respective 



