1 68 THE STRUCTURE AND LIFE OF BIRDS ch\p. 



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. 1 



1 Vide Seebohm's Siberia in Europe, p. 147 



