The second sub-order of the Rasores is that of the Columbacei or Gemitores, comprising the
Fig. 340. - Columbidae. Rock-pigeon (Columba livia).
Doves and Pigeons, and often raised to the rank of a distinct order under the name of Columbae. The Columbacei are separated from the more typical members of the Rasores by being furnished with strong wings, so as to endow them with considerable powers of flight. In place, therefore, of being chiefly ground-birds, they are to a great extent arboreal in their habits, and in accordance with this the feet are slender, and are well adapted for perching. There are four toes, three in front and one behind, and the former are never united towards their bases by a membrane, though the base of the outer toe is sometimes united to that of the middle toe. The hallux is articulated on the same plane as the other toes, and touches the ground in walking. Lastly, they are all monogamous, and pair for life; in consequence of which fact, and of their being readily susceptible of domestication, they present an enormous number of varieties, often so different from one another that they would certainly be described as distinct species if found in a wild state. It seems certain, however, that all the common domestic breeds of Pigeons, however unlike one another, are really descended from the Rock-pigeon (Columba livia), which occurs wild in many parts of Europe, and has retained its distinguishing peculiarities unaltered for many centuries up to the present day. Finally, the young of the Columbacei are born in a naked and helpless state, whilst those of the Gallinacei are "precocious," and can take care of themselves from the moment of their liberation from the egg.
Of the various living birds included in this section, the true Pigeons (Columbidae) are too well known to require any description ; but the Ground-pigeons (Gouridae) depart to some extent from this type, being ground-loving birds, more closely allied to the ordinary Gallinacei. The Treronidae, or Tree-pigeons, are exclusively found in the Old World, in its warmer parts, and are arboreal in their habits, living principally upon fruits. The Didunculidae are a small group, comprising only the little Diduncnlus strigirostris of the Navigator Islands. In this curious bird the wings are well developed, enabling it to lead an arboreal life, and the upper mandible of the beak is strongly arched and hooked towards its tip. The Didunculus is of special interest as having certain relationships to the now extinct Dodo, the representative of the family Dididae. The Dodo (Didus ineptus, fig. 341) formerly inhabited the island of Mauritius, in great numbers, but the last record of its occurrence dates from the year 1681. It was a large and heavy bird, bigger than a swan, and entirely unlike the Pigeons in general appearance. The wings were rudimentary and completely useless as organs of flight. The legs were short and stout, the feet had four toes each, and the tail was extremely short, carrying, as well as the wings, a tuft of soft plumes. The beak (unlike that of any of the Columbacei except the little Didunculus strigirostris) was strongly arched towards the end, and the upper mandible had a strongly-hooked apex, not at all unlike that of a bird of prey. The Dodo owed its extermination to the fact that it was good to eat, and that it was unable to fly. At present all the known remains of this singular bird that exist are some old, but apparently faithful, oil-paintings, and a few fragmentary remains, to which explorations in the Recent deposits of the island have added a large number of bones. Allied to the Dodo, and, like it, incapable of flight, is the Solitaire (Pezophaps) of Rodriguez, a small island lying about 300 miles to the east of Mauritius. Its last recorded appearance was in the year 1693. It had longer legs than the Dodo, and its bill was less strongly arched.
Fig. 341. - Skeleton of the Dodo (Didus ineptus), restored. (After Owen.)
As regards the distribution of the Rasores in time, the order is not known to have made its appearance sooner than the Eocene Tertiary (the Palaeortyx of the Paris basin). In the Miocene period occur the remains of both Gallinaceous and Columbaceous birds, one of the most noticeable of the former being a Turkey (Meleagris antiquns) from the Miocene of Colorado. The later Tertiary and Post-tertiary deposits have also yielded the bones of various Rasorial birds.