168 THE STRUCTURE AND LIFE OF BIRDS cCHAp. 
top of the Tibiotarsus (drumstick) partly from the 
lower end of the Femur or thigh-bone. When the 
leg bends at the ankle, there is a pull upon the 
tendons, the muscles are stretched, the toes are 
bent and grasp the perch on which the. bird sits. 
Thus he is maintained in position by his own weight,. 
which bends the leg and so causes the toes to grip. 
The strain on the muscles is, probably, not great. 
Chickens and, I believe, other birds rest their breast- 
bone upon the perch, and so get support nearly in the 
vertical line in which lies the centre of gravity. The grip 
of the toes, therefore, is wanted only to steady them. 
This bending of the toes, as a necessary consequence of 
bending the leg at the ankle-joint, is not altogether 
peculiar to birds. A squirrel’s toes will open or close ac- 
cording as his leg is straightened or bent. In birds what 
was once, probably, a trifling or useless feature has been 
developed in order to supply a vital need. Birds, such 
as Gulls, which do not sleep upon a perch and are rather 
ill at ease upon one, have this toe-grip only in a most 
rudimentary form. I have seen the Black-headed Gull 
alight on railings, and at the Zoological Gardens, when 
in a small aviary where they have not much ground to 
wander over, Gulls will remain perched for some time, 
though apparently uncomfortable, on the thin bar 
allotted them. This is no proof, however, that they 
could sleep upon a perch. Others, which are not 
ordinarily perchers, are quite capable of adopting 
arboreal habits. The.annual flooding of great tracts 
of country in Siberia has brought this about in the 
case of the Snipe 
| Vide Seebohm’s Siberza in Europe, p. 147 
