ON THE MIGRATION OF BIRDS. 4 
Taste [V.—Birds which are partially Periodical. 
Birds. 
Throstle (Turdus musicus) 
Starling (Sturnus vulgaris) 
Common Bunting (Emberiza miliaria) ...... Mar. 6} 38] ,, 16] 56 
Reed-Bunting (Hmberiza scheniclus) ......+0 » 10) 46) ,, 4] 55 
Greenfinch (Mringilla chloris) ...ccccceceere| 5, 14) 48} ,, 18) 54 
Lapwing (Vanellus cristatus) wccscceceesees| 5, 27} 49 | Sept. 29] 57 
Lesser Redpole (Fringilla linaria) ............ April 10} 47 | Oct. 21) 47 
Mountain-Linnet (Fringilla montium) ...... », 22} 50 | Sept. 17} 56 
Grey Wagtail (Motacilla boarula) 57 | April 11| 44 
Merlin (Falco @salon) .........60.0008 49 | ,, 
Ring-Ouzel (Turdus torquatus) ........::000 49 
REMARKS. 
The gradual increase of temperature in spring, and 
its decrease in autumn, are circumstances which seem 
to be so closely connected with the appearance and 
disappearance of the Periodical Birds that they have 
long been regarded as the primary causes of those 
phenomena. In reflecting on this very generally re- 
ceived opinion, it occurred to me that I had never met 
with any attempt to ascertain how nearly the tempe- 
rature of the time of the appearance of the Periodical 
Birds coincides with the temperature at the time of 
their departure; and, as this is a consideration of 
much importance, I have endeavoured, at least in some 
measure, to supply the deficiency. 
According to the Tables, it seems that, with a few 
exceptions, the temperature is considerably higher 
when the Periodical Summer Birds withdraw than it 
