on bird, song.



307



while performing their nocturnal journeys, but the difficulty of

identifying the species and their calls is obvious. It seems certain

that if not now, at any rate during the evolution of the species some

reason must have been attached to these calls, other than arising from

the ordinary needs of denoting proximity. But as so very little is

known up to the present about migration itself, it is difficult to arrive

at any really satisfactory explanation of these signal calls.


Finally we come to the love call, which precedes the song

proper. Some species possess a very simple love call, which may

I’esemble the call note, but differs considerably in strength and power

of utterance. For instance, the call note of the nuthatch is a simple

metallic note, often reiterated ; the love call is the same note, more

l’apidly delivered in a hell-like silvery tone. Other species possess an

entirely distinct love call. The great tit, besides its pretty little song of

“ spring coming, spring coming,” which may be heard on and off

during the whole year, and every hour of the day during the spring,

has a single clear note, which is only heard at the height of the nesting

season. One more point may be mentioned with regard to these love

calls. The hen chaffinch has a call peculiar to her sex, a soft and

rather plaintive note, which is frequently made use of early in the

season ; whether the females of other species are gifted with a special

call is at present not known for certain.


The precise cause and meaning of the song proper, is still a

vexed question, and opinions and theories vary considerably. These

may be roughly divided into two categories : (l) That singing is


primarily and solely a secondary character, (like other physical

characters of sexual selection) ; (2) that song is an expression of


nervous vitality, and may be called forth, by many and varying

emotions. The first theory, which has long held the field, rests on

Darwin’s theory of sexual selection, i.e. that the female selects the

male by virtue of his superior strength, exhibited by his physical

attractions, (plumes of the bird of paradise, etc.) and vocal powers,

in comparison with those of his rivals. There is much evidence to

support this theory, and although it is too big a subject to discuss

fully in this paper, the chief points may be briefly set down. Song

is primarily a specialised development of the love call, the special

use of which is to call and attract hen birds. Birds’ song being



