THE MOVEMENTS. 
25 
covered with layers of duckweed, or some other aquatic 
plant, so as to give the resistance necessary, while 
crossing so light a bridge in their wanderings. Others, 
not handy with their feet on land, move in a similar 
manner, seeking to keep their foothold or establish their 
equilibrium with the assistance of their wings; as, for 
example, the Guillemot, when forced to make its way 
across a space of level ground. The pace of the most 
rapid runners among birds is about equal to that of the 
fleetest mammal. 
Climbing requires the use of one, and, according to cir¬ 
cumstances, even of two members of the body more than 
walking,—the beak and tail; though the feet must always 
do the principal portion of the work. This is effected in 
a variety of ways in accordance with the formation of the 
body and the functions of the bird; it may be, with or 
without the assistance of the beak and tail-feathers. All 
Woodpeckers climb by means of a series of springs or 
jumps, but only in ascending, inasmuch as they hang on 
to the side of a tree by their claws, pressing the tail, 
which is furnished with strong elastic feathers, against 
the tree. Before they first make the spring, which is 
always very short, the tail is so pressed against the tree 
that it becomes much bent in the middle; they then 
advance by a hop with the feet, the elastic pressure 
of the tail assisting the operation. Treecreepers climb 
in the same manner, although, from their ability to 
cling-on to the lower side of a limb, they are able to 
run both up and down. The Nuthatch does the same, 
simply by means of its remarkably long feet, which are 
furnished with large hooked claws. The Wallcreeper 
(Tichodroma muraria) ascends, in a similar manner, old 
over-hanging walls and rocks, but has to assist itself with 
E 
