It is an interesting evidence of the bird's keen instinct that where
nests are built on lonely roads and away from houses they are
noticeably deeper, and so better protected from bird enemies. The same
thing is sometimes noticed of nests built in maple or apple trees,
which are without the protection of drooping branches, upon which
birds of prey can find no footing. Some wise birds secure the same
protection by simply contracting the neck of the nest, instead of
building a deep one. Young birds building their first nests seem
afraid to trust in the strength of their own weaving. Their nests are
invariably shallow, and so suffer most from birds of prey.
In the choice of building material the birds are very careful. They
know well that no branch supports the nest from beneath; that the
safety of the young orioles depends on good, strong material well
woven together. In some wise way they seem to know at a glance whether
a thread is strong enough to be trusted; but sometimes, in selecting
the first threads that are to bear the whole weight of the nest, they
are unwilling to trust to appearances. At such times a pair of birds
may be seen holding a little tug-of-war, with feet braced, shaking and
pulling the thread like a pair of terriers, till it is well tested.
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