--many of the birds running or hopping
on the ground to search for insects in the loose soil or under dead
leaves, while others explore the thorny bushes. My observations of these
small bands lead me to believe that everywhere in South America the
Dendrocolaptidae are the first in combining to act in concert, and that
the birds of other families follow their march and associate with them,
knowing from experience that a rich harvest may be thus reaped. In the
same way birds of various kinds follow the movements of a column of
hunting ants, to catch the insects flying up from the earth to escape
from their enemies; swallows also learn to keep company with the
traveller on horseback, and, crossing and recrossing just before the
hoofs, they catch the small twilight moths driven up from the grass.
To return to the subject of voice. The tree-creepers do not possess
melodious, or at any rate mellow notes, although in so numerous a family
there is great variety of tone, ranging from a small reedy voice like
the faint stridulation of a grasshopper, to the resounding,
laughter-like, screaming concerts of Homorus, which may be heard
distinctly two miles away. As a rule, the notes are loud ringing calls;
and in many species the cry, rapidly reiterated, resembles a peal of
laughter. With scarcely an exception, they possess no set song; but in
most species that live always in pairs there are loud, vehement,
gratulatory notes uttered by the two birds in concert when they meet
after a brief separation.
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