cry, and finds
again its melodious song; and even the secretive Grasshopper-Warbler
crawls out of the midst of the thicket in order to "reel," just as, for
a similar reason, Savi's Warbler climbs to the top of a tall reed. In
fact the males of most species, when they are finally established on the
breeding grounds, make themselves as conspicuous as possible by sight
and by sound. And since the sounds produced by no two species are
exactly alike, the females are able to recognise their prospective
mates, and the males that are still in search of ground have ample
warning if that upon which they are treading is already occupied. So
that you see, from the remarkable development of the vocal powers in the
male, there follow two important results--"recognition" and "warning."

We here turn from song as the expression of an instinctive disposition,
and the question of what calls forth this expression, to the impression
produced by the song on the hearer.

Most birds have a call-note or a number of call-notes, which, generally
speaking, are specifically distinct. But to the human ear they are not
always so, perhaps because our power of hearing is less sensitive than
that of a bird, and unable to appreciate delicate differences of tone.
Be this as it may, however, the fact remains that we often find it
difficult, and in not a few cases impossible, to recognise a bird merely
by its call. The plaintive notes of the Willow-Warbler and of the
Chiffchaff are to our ears very closely akin, so, too, are those of the
Marsh-Warbler and of the Reed-Warbler, and there is a great resemblance
between the hissing sound produced by the two Whitethroats. In Co.
Donegal I have been deceived by the spring-call of the Chaffinch which,
owing possibly to the humidity of the atmosphere, is, there, almost
indistinguishable from the corresponding note of the Greenfinch. The
Yellow Bunting and the Cirl Bunting frequently make use of a similar
note, so do the Curlew and the Whimbrel. In fact, numberless instances
could be quoted in which notes appear to us identical, and, as a rule,
the more closely related the species, the more difficult it becomes to
distinguish the sounds--alike in plumage, alike in behaviour, alike in
emotional manifestation, it would be surprising if they were not alike
in voice. But the moment we pass from the call-notes to a consideration
of the songs we are faced with a very remarkable fact, for not only are
these readily disti