FEET OF BIRDS. 267. 
or such as have their feet adapted not only for 
perching on trees, but for walking upon the ground. 
Some unite both these powers in the greatest per- 
fection. The crow, the thrush, the robin, sparrow, 
and numerous other familiar birds, are as often 
seen in one situation as the other, and in both are 
equally at home. But the swallow is rarely seen on 
the ground, save when employed, by the side of a 
wet puddle, in picking up particles of mud for its 
nest. The flycatcher also (taking our common 
grey species as a genuine example of the family) 
very rarely sets its feet upon the earth, and then 
but for a moment. The larks, on the other hand, as 
rarely perch upon trees; the ground is more pecu- 
liarly their element, and the wagtails do the same. 
Nevertheless, all these families come into the general 
order of perching birds (Insessores), because they 
have those external characters which so distinguish 
them, yet modified in different degrees and pro- 
portions. Nature, ever watchful over her creatures, 
always makes up to them in one way what she 
takes from them in another. Of what use or ad- 
vantage would it be to the wagtail, that it should 
run up trees like a woodpecker, or fly with the 
swiftness of a swallow, when its natural food is placed 
close to the ground? If all birds were equally 
endowed, if all could walk, climb, run, fly, or swim 
with the same ease and with the same perfection, 
they must all have a similarity of structure adapted 
for such powers; and that variety, which is one of 
the greatest wonders of the creation, would never have 
existed. We therefore see gradations of the same 
quality—those, for instance, of perching or of walk- 
