410 USEFUL BIRDS. 
fectly smooth surface. Nesting boxes mounted on poles may 
be guarded in this way. Zinc is the best material. A wide 
piece of wire netting, shaped like a hat brim, and fastened 
around a tree, will prevent cats and squirrels from climb- 
ing it. A smooth, 
tall, slim pole, made 
of a peeled sapling 
pine set in the open, 
is rarely climbed by 
cats or squirrels. 
Thick thorn bushes 
often serve as safe 
nesting places for 
birds. Bundles of 
thorny sticks tied 
around tree trunks 
will keep cats out of 
the trees. An island 
in a small artificial 
: Fig. 1'71.— Zine bands to prevent cats or squirrels pond is also a refuge 
from climbing trees or poles. fos eats. The bask 
cat-proof fence for a city garden is that used by Mr. William 
Brewster at Cambridge. It is made of wire netting some 
six feet in height, surmounted by a fish seine of heavy twine, 
which is fastened to the top of the wire. The top of the net is 
then looped to the ends of long, flexible garden stakes. This 
fabric gives beneath any weight, and offers so unstable a foot- 
ing that no cat ever succeeds in scaling it. Mr. Brewster's 
garden has become famous for the numbers of birds that breed 
there, and the migrants that visit it year by year. 
THE PROTECTION OF FARM PRODUCTS FROM BIRDS. 
Serious losses sometimes occur from injury inflicted on 
crops or poultry by birds. It is well to remember, how- 
ever, that, while the harm done by birds is conspicuous, 
the compensating good that they do is usually unnoticed. 
In most cases it is best not to kill them, but to protect both 
birds and crops; for by killing too many birds we may dis- 
turb the biological equilibrium, and bring about a greater™ 
