250 THE ESSEX NATURALIST. 
Although the Song Thrush is so close to the Redwing in many 
ways, one difference can be noted. Flocks of Thrushes are al- 
ways “‘ loose,’ the birds hanging together in a disjointed flock. 
The Redwing frequently flocks as close as Starlings, and will 
often perform elaborate aerial manceuvres after the manner 
of Starlings ; in my experience these large movements, wit- 
nessed, of course, in daylight, are carried out silently. Whenin 
small flocks the birds often utter their “‘ seep ”’ call. 
i \On closely comparing Thrush with Redwing a difference: in 
the eye becomes noticeable. The Thrush has by far the bigger 
eye. This difference cannot easily be shown in figures, but my. 
measurements are 5 mm. for Redwing and 6 mm. for Thrush. 
The difference is more apparent in the bones of the skull, where 
the rule can be placed on the frontal bone between the orbits. 
The space is 4 mm. in the Thrush, but 6 mm. in the Redwing. 
I do not think that size of eye is generally a safe ae to the 
habits of a bird ; 1t may be in this case. 
The Song Tare is much more often noticed on migration 
than is the Redwing, although apparently this curious point 
has never attracted consideration. My impression is. that for 
every hundred Thrushes met with at lighthouses or lightships 
there cannot be more than about thirty Redwings. The figures 
I have used have been drawn from such schedules as those pub- 
lished by the Committee on the Migration of Birds, those by 
Barrington on Migration in Ireland, Herluf Winge on Danish 
Lighthouses, Gaetke on Heligoland, and Dr. Eagle Clarke .on 
British and other stations. For example, when Dr. Clarke spent 
a month on the Kentish Knock Lightship, off the Essex coast 
{17th September to 18th October, 1923) he did not record a single. 
Redwing, although Song Thrushes were abundant. The date, of 
course, is not late enough for safe deductions to be made; but 
Gaetke, in his “‘ Heligoland”’ speaks clearly of the comparative 
rarity of the Redwing and the extreme abundance of Song 
Thrushes. 
-In my 1911 paper I expressed the opinion that nocturnal 
Redwings flew only in fine weather—that is, on nights fairly 
free from wind. I would modify this opinion ; I consider that, 
roughly speaking, the birds may be heard any night, without 
reference either to the weather or the state of the moon. On 
a stormy night the conditions are not suitable for outdoor vigils ; 
