426 THE LIFE OF A BIRD. 



on land, they do so with some difficulty and with 

 a peculiar gait, showing that their proper element 

 is the wave, and not the land. But in the water 

 how different are its movements ! The singular 

 feet are now found to be beautiful instruments 

 for propelling the bird along the yielding surface. 

 When drawn forwards, the thin edge of the foot 

 passes like a knife through the water, but in 

 giving the back stroke, or impulse, the webs are 

 forced wide out, and thus offer a very great 

 resistance against which the bird acts and thrusts 

 itself onwards. In addition to this, the joints of 

 the whole limb are so formed that it can be moved 

 with facility in a variety of directions, and/thus 

 impel the body in any course which may be neces- 

 sary to the bird in following its prey through the 

 water. The grebes thus plunge forward with 

 great power and speed, occasionally making use of 

 the wings to assist them in their career. 



Very different from either of these forms of feet 

 is the climbing foot of birds. The toes in the foot 

 of the wood-pecker are four in number, and in 

 climbing, the two front ones act against the two 

 hinder ones. The front claws penetrate into the 

 crevices or irregularities of the bark, and the hind 



