and have found that in some cases no young-were reared at all; in other cases one or two young; while, as often as not, the young actually reared were only parasitical starlings after all. I have still to speak of the voice of the tree-creepers, an important point in the study of these birds; for, though not accounted singers, some species emit remarkable sounds; moreover, language in birds is closely related to the social instinct. They seem to be rather solitary than gregarious; and this seems only natural in birds so timid, weak-winged, and hard pressed. It would also be natural to conclude from what has been said concerning their habits that they are comparatively silent; for, as a rule, vigorous social birds are loquacious and loud-voiced, while shy solitary kinds preservo silence, except in the love season. Nevertheless the creepers are loquacious and have loud resonant voices; this fact, however, does not really contradict a well-known principle, for the birds possess the social disposition in an eminent degree, only the social habit is kept down in them by the conditions of a life which makes solitude necessary. Thus, a large proportion of species are found to pair for life; and the only reasonable explanation of this habit in birds--one which is not very common in the mammalia--is that such species possess the social temper or feeling, and live in pairs only because they cannot afford to live in flocks. Strictly gregarious species pair only for the breeding season. In the creepers the attachment between the birds thus mated for life is very great, and, as Azara truly says of Anumbius, so fond of each other's society are these birds, that when one incubates the other sits at the entrance to the nest, and when one carries food to its young the other accompanies it, even if it has found nothing to cany. In these species that live in pairs, when the two birds are separated they are perpetually calling to each other, showing how impatient of solitude they are; while even from the more solitary kind, a high-pitched call-note is constantly heard in the woods, for these birds, debarred from associating together, satisfy their instinct by conversing with one another over long distances.