Again, when we consider a large number of species of different groups, we find that there is not with the Tree-creepers, as with most families, any special habit or manner of life linking them together; but that, on the contrary, different genera, and, very frequently, different species belonging to one genus, possess habits peculiarly their own. In other families, even where the divergence is greatest, what may be taken as the original or ancestral habit is seldom or never quite obsolete in any of the members. This we see, for instance, in the woodpeckers, some of which have acquired the habit of seeking their food exclusively on the ground in open places, and even of nesting in the banks of streams. Yet all these wanderers, even those which have been structurally modified in accordance with their altered way of life, retain the primitive habit of clinging vertically to the trunks of trees, although the habit has lost its use. With the tyrant birds--a family showing an extraordinary amount of variation--it is the same; for the most divergent kinds are frequently seen reverting to the family habit of perching on an elevation, from which to make forays after passing insects, returning after each capture to the same stand. The thrushes, ranging all over the globe, afford another striking example. Without speaking of their nesting habits, their relationship appears in their love of fruit, in their gait, flight, statuesque attitudes, and abrupt motions.
With the numerous Dendrocolaptine groups, so
242 The Naturalist in La Plata.
widely separated and apparently unrelated, it would be difficult indeed to say which, of their most striking habits is the ancestral one. Many of the smaller species live in trees or bushes, and in their habits resemble tits, warblers, wrens, and other kinds that subsist on small caterpillars, spiders, &c., gleaned from the leaves and smaller twigs. The Anumbius nests on trees, but feeds exclusively on the ground in open places; while other ground-feeders seek their food among dead leaves in dense gloomy forests. Coryphistera resembles the lark and pipit in its habits; Cinclodes, the wagtail; Geobates a Saxicola; Limnornis lives in reed beds growing in the water; Henicornis in reed beds growing out of the water; and many other ground species exist concealed in the grass on dry plains; Homorus seeks its food by digging in the loose soil and dead leaves about the roots of trees; while Geo-sitta, Furnarius, and Upercerthia obtain a livelihood chiefly by probing in the soil. It would not be possible within the present limits to mention in detail all the different modes of life of those species or groups which do not possess the tree-creeping habit; after them comes a long array of genera in which this habit is ingrained, and in which the greatly modified feet and claws are suited to a climbing existence. As these genera comprise the largest half of the family, also the largest birds in it, we might expect to find in the tree-creeping the parental habit of the Dendrocolaptidae, and that from these tropical forest groups have sprung the widely-diverging thicket, ground, marsh, sea-beach, and rock-frequenting groups. It happens, however,
The Woodhewer Family. 243
that these birds resemble each other only in their climbing feet; in the form of their beaks they are as wide apart as are nuthatches, woodpeckers, crows, and curlews. They also differ markedly in the manner of seeking their food. Some dig like woodpeckers in decayed wood; others probe only in soft rotten wood; while the humming-bird-billed Xiphorhynchus, with a beak too long and slender for probing, explores the interior of deep holes in the trunks to draw out nocturnal insects, spiders, and centipedes from their concealment. Xiphoco-laptes uses its sword-like beak as a lever, thrusting it under and forcing up the loose bark; while Dendrornis, with its stout corvine beak, tears the bark off.
In the nesting habits the diversity is greatest. Some ground species excavate in the earth like kingfishers, only with greater skill, making cylindrical burrows often four to five feet deep, and terminating in a round chamber. Others build a massive oven-shaped structure of clay on a branch or other elevated site. Many of those that creep on trees nest in holes in the wood. The marsh-frequenting kinds attach spherical or oval domed nests to the reeds; and in some cases woven grass and clay are so ingeniously combined that the structure, while light as a basket, is perfectly impervious to the wet and practically indestructible. The most curious nests, however, are the large stick structures on trees and bushes, in the building and repairing of which the birds are in many cases employed more or less constantly all the year round. These stick nests vary greatly in form,