Feet and Legs 367 
We have hardly to leave the group of birds to which 
the crow belongs to find dozens of interesting and unex- 
pected adaptations of the feet to unusual habits. For 
example, the Rhinoceros-birds of Africa attach them- 
selves to some of the larger mammals, such as buffalos, 
rhinoceri, or antelopes, and spend much of their time 
in freeing these animals from troublesome ticks and other 
parasites. The power which these birds possess in their 
feet and legs is remarkable. Millais says of them: ‘The 
prehensile power of the claws is, as I found by experience, 
so great that when a dead bird which had grown stiff 
was thrown on to the back or sides of an ox, so that the 
feet touched the animal’s hide, the claws held fast at 
once and could not be withdrawn. It is most interesting 
to note the way in which a party of these birds will move 
about on the body of a horse or ox, searching every part of 
him as they run or hop over it in the most lively fashion. 
At the risk of being accused of telling a traveller’s yarn, 
I must state the fact that they can hop backward quite 
as well as forward, and they often make long drops down- 
ward from the shoulders to the foreleg, or down the side 
of the animal whose coat they are engaged upon. It 
is quite immaterial to them how or in what direction 
they move.” 
No hard and fast laws can be laid down, but it is gener- 
ally the rule that birds which are especially at home in 
the trees usually hop with both feet simultaneously 
when on the ground. Ground nesters and feeders, such 
as the Meadow Lark, Bob-white, and Vesper Sparrow, 
usually walk or run. 
