Probably the sober and generally protective colouring of the tree-creepers, even with the variability and adaptiveness displayed in their habits superadded, would be insufficient to preserve such feeble birds in the struggle of life without the further advantage derived from their wonderful nests. It has been said of domed nests that they are a danger rather than a protection, owing to their large size, which makes it easy for carnivorous species that prey on eggs and young birds to find them; while small open nests are usually well concealed. This may be the case with covered nests made of soft materials, loosely put together; but it cannot be said of the solid structure the tree-creeper bnilds, and which, as often as not, the bird erects in the most conspicuous place it can find, as if, writes Azara, it desired all the world to admire its work. The annual destruction of adult birds is very great--more than double that, I believe, which takes place in other passerine families. Their eggs and young are, however, practically safe in their great elaborate nests or deep burrows, and, as a rule, they lay more eggs than other kinds, the full complement being seldom less than five in the species I am acquainted with, while some lay as many as nine. Their nests are also made so as to keep out a greater pest than their carnivorous or egg-devouring enemies--namely, the parasitical starlings (Molo-thrus), which are found throughout South America, and are excessively abundant and destructive to birds' nests in some districts. In most cases, in the
252 The Naturalist in La Plata.
big, strong-domed nest or deep burrow, all the eggs are hatched and all the young reared, the thinning, out process commencing only after the brood has been led forth into a world beset with perils. With other families, on the contrary, the greatest amount of destruction falls on the eggs or fledglings. I have frequently kept a dozen or twenty pairs of different species--warblers, finches, tyrants, starlings, &c.--under observation during the breeding season, 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
The Woodhewer Family. 253
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 Anumbiüs, 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.
The foregoing remarks apply to the Dendrocolap-tidae throughout the temperate countries of South America--the birds inhabiting extensive grassy plains and marshes, and districts with a scanty or scattered tree and bush vegetation. In the forest areas of the hotter regions it is different; there the birds form large gatherings or "wandering bands," composed of all the different species found in each district, associated with birds of other families--wood-peckers, tyrant-birds, bush shrikes, and many others. These miscellaneous gatherings are not of rare occurrence, but out of the breeding season are