144 THE BIRDS OF SHERWOOD FOREST. 
odd, festooning flight from tree to tree, but not invariably 
so, as I have heard it both when clinging to a tree and 
when on the ground. The latter situation is only fre- 
quented where there are anthills, when it willingly leaves 
its strongholds the trees, to search for its favourite 
food. 
Its motions on the trees, for which it is so admirably 
fitted, are well worth watching. I never saw it by any 
chance perch on the upper side of a bough, but it is 
fond of clinging to the under side, where during the day 
insects chiefly congregate. It is on the perpendicular 
trunk, however, that it is most at home. Commencing 
at the base it pursues a spiral course to the top, prying 
into every chink and crevice, tapping here and there 
with vigorous and rapid strokes to alarm its insect prey. 
I have remarked previously that nearly all the old 
oaks in the forest have suffered the loss of their tops by 
the agency of wind and lightning, aided by natural 
decay. Sometimes you may see the upper portion of 
one of these venerable trunks quite denuded of its bark, 
and riven with many fissures, though the tree is all the 
while in vigorous growth. On some of these I have 
often noticed the green woodpecker practise a singular 
feat. Placing its bill in one of the long cracks I have 
mentioned, it produces, by an exceedingly rapid vibra- 
tory motion, a loud crashing noise, as if the tree was 
violently rent from top to bottom. I have heard it 
when the sound was so loud and sudden that the woods 
rang again. For a long time I was at a loss to know 
how it was produced, but I one day witnessed the pro- 
cess, and have seen it several times since. It would 
effectually rouse up all the insects, for it seemed as if the 
tree quivered from top to bottom. 
