62 THE FLIGHT OF BIRDS 
all the heads turned one way, the object being to 
follow with the eye t®@ movements of the leader or 
leaders of the flock ? 
Good Steerers and Bad. 
There are good steerers and bad _steerers. 
Contrast the Swallow, the Lapwing, or the Sparrow- 
Hawk, those adepts at sudden swerving and 
doubling, with the Duck! The Duck becomes the 
slave of his own ponderous momentum, and changes 
his course slowly and with effort. The Swallow, 
the Lapwing and the Sparrow-Hawk have all of 
them a fine expanse of tail, while the Duck’s is small 
in area and, what there is of it, feeble. Efficiency 
or inefficiency of tail, no doubt, accounts for a 
great deal. But it is not the only factor to be 
considered. The Duck, though very strong, is 
lacking in agility; the three other birds have far 
more suppleness, I believe, notably at one im- 
portant point. Though birds’ backbones are, 
below the neck, very stiff, yet they allow of a good 
deal of bend, either up and down or sideways, at the 
waist. I have measured the amount of sideways 
bend in some few species and found that, as far as 
my far from complete evidence goes, good steerers 
Angle formed by backbone 
bending sideways at waist. 
Kestrel .. a ma ‘Sia: 
Swallow ot ne i A 
Pwitt. %. ik ye . as 
Common Tern fe: Vio baa 
Kestrel (another specimen) .. 156° 
Domestic Duck ay . 66" 
