OCR Text |
Show 106 DR. R. O. CUNNINGHAM ON RHEA. [Feb. 7, have picked up its characteristic white-tipped feathers in various localities in the plains *. I regret that I have almost nothing to add to our knowledge of the habits of Rhea americana, as it was but seldom that I noticed live examples, and then, owing to their speed of foot, only for a few minutes at a time. I can, however, corroborate the testimony of Mr. Darwin with regard to the facility with which the species takes to the water, one of the officers of the * Nassau,' a very careful and trustworthy observer, having on one occasion observed several individuals on the south of St. Jago Bay (Strait of Magellan) escape from threatened danger by running into the sea. Further, I may add that, although indiscriminate in its feeding like other members of the tribe, it appears, in common with the Upland Goose (Chloephaga magellanica), to cherish a special predilection for the red berries of the Empetrum rubrum, a plant very abundant on the grassy plains. Some months ago Mr. Sclater was good enough to place in my hands for examination and comparison two nearly perfect skeletons of Rhea americana and R. darwinii; and I now venture to lay a few brief notes on the subject before the Society. Both specimens were those of females, that of Rhea americana having apparently belonged to an adult bird, while that of R. darwinii bore unequivocal traces of immaturity. It is necessary, of course, to bear this fact in mind, as many of the differences observable are without doubt due to the different ages of the individuals, while a certain number are possibly only the result of individual variation, and others may probably with justice be regarded as marks of specific distinction. Regarded in toto, the differences between the two skeletons are comparatively slight, though perhaps not more so than those which commonly obtain between closely allied species. In the following observations, I would premise that it is not m y intention to attempt the very elaborate task of giving a full description of the osteology of the two species, as to do that in a complete and satisfactory manner would have necessitated the examination of a much larger number of specimens than I have had at m y command, but to content myself with noting those points which appear to be of the most salient character. Cranium.-Beginning with the cranium, I may remark that its general contour is very much the same in both species, though certain minute marks of distinction between the individual bones are recognizable on a careful inspection. Thus in the cranium of the specimen of Rhea darwinii (in which nearly all the bones are still unanchylosed) the vertical ridge on the supraoccipital is considerably more elevated than in R. americana, and the portion of the hori- * When Dr. Adolf Booking, in his interesting " Monographie des Nandu oder siidamerikanischen Strausses," in Wiegmann's Archiv for 1863 (for a reference to which I a m indebted to Mr. Sclater), speaks of R. americana and R. darwinii as climatic varieties comparable with those of Ferdix cinerea, it is difficult to avoid the conclusion that be has never carefully examined specimens of the two birds; and his hypothesis is disproved by the fact of their occurring in the same district. |