1881.] J. C. Douglas — On the Perching of Birds. 55 



sleeping bird is thus held securely on his perch by the weight of his own 

 body ; and some authors add " without fatigue." I purposely omit other 

 details such as the structure of the joints by which the leg is stiffened laterally 

 and vertically. 



In the first instance, if the toes were flexed by the weight of the body 

 putting tension on the muscles, this could not happen without causing 

 fatigue, for the mere tension of a muscle influences its nutrition and waste, 

 hence muscular exhaustion would result. That exhaustion is felt, is proved 

 by the bird using only one leg while resting the other, also by the fact that it 

 changes the leg from time to time, and that on waking, the foot is opened 

 as if cramped. The evidence in favour of Borelli's explanation is anatomi- 

 cal ; if the leg of a dead bird be bent under certain circumstances, the toes 

 close together, and the foot may be so made to seize the finger of the 

 experimentalist ; if the leg be dissected, the movements of the parts may 

 be clearly seen to bring about the result. But although this takes place 

 in the dead bird, and is therefore possible in the live one, it by no means 

 follows that this is the mechanism of perching. Even this purely anatomi- 

 cal phenomenon, which has been relied on to prove the physiological condi- 

 tions, is not invariably present, for if a bird die with its leg contracted and 

 its claw extended, the leg may be extended and flexed without closing the 

 toes ; in fact, the production of the phenomenon depends on the condition 

 of the muscles after death. If the bird dies with its claws open and leg 

 extended, the flexor muscles of the toes are not opposed by the extensors, 

 they shrink and lose their elasticity when they die, and the phenomenon is 

 produced ; if they are opposed by the extensors, and the leg is bent, they 

 lose their elasticity but cannot contract, and are therefore, when dead, elon- 

 gated, and the phenomenon is not produced. It is very obvious in the live 

 bird these muscles are elastic, and their exact length while living may be 

 anything between the above extremes, but whether they act in the manner 

 stated, depends entirely on their condition in the living bird, which is standing 

 with his legs bent at their normal angle, these muscles being opposed by 

 another set of muscles, and both being under the control of the bird's will. 

 Because bending the leg bends the toes in a dead bird, in which the muscles 

 have lost their elasticit}^ and become shortened, to assume that therefore in 

 the live bird, the mechanism acts precisely in the same manner, is an 

 assumption in my opinion which is contradicted by observation of the 

 living bird, and by the consideration of the general laws of which the 

 perching bird is but a particular instance. Mammals and birds, on plane 

 surfaces, maintain the upright attitude by balancing themselves, and 

 birds standing on two legs on a perch do not, unless the perch be shaken, 

 hold the perch, they simply balance themselves ; the birds are prevented 

 from slipping by the soft under-surface of the foot, which gives a 

 foot -hold little liable to slip on the rough bark of a tree, and if the perch 



