Thus, those which were heard number 192. Of these the language of 7 species has been completely forgotten, and of 31 the sound-impressions have now become indistinct in varying degrees. Deducting those whose notes have become silent and are not clearly heard in the mind, there remain 154 species which are distinctly remembered. That is to say, when I think of them and their language, the cries, calls, songs, and other sounds are reproduced in the mind.
Studying the list, in which the species are ranged in order according to their affinities, it is easy to see why the language of some, although not many, has been lost or has become more or less indistinct. In some cases it is because there was nothing distinctive or in any way attractive in the notes; in other cases because the images have been covered and obliterated by others--the stronger images of closely-allied species. In the two American families of tyrant-birds and woodhewers, neither of which are songsters, there is in some of the closely-related species a remarkable family resemblance in their voices. Listening to their various cries and calls, the trained ear of the ornithologist can easily distinguish them and identify the species; but after years the image of the more powerful or the better voices of, say, two or three species in a group of four or five absorb and overcome the others. I cannot find a similar case among British species to illustrate this point, unless it be that of the meadow- and rock-pipit. Strongly as the mind is impressed by the measured tinkling notes of these two songs, emitted as the birds descend to earth, it is not probable that any person who had not heard them for a number of years would be able to distinguish or keep them separate in his mind--to hear them in their images as two distinct songs.
In the case of the good singers in that distant region, I find the voices continue remarkably distinct, and as an example will give the two melodious families of the finches and the troupials (Icteridae), the last an American family, related to the finches, but starling-like in appearance, many of them brilliantly coloured. Of the first I am acquainted with 12 and of the second with 14 species.