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Watching THE PLOVER-LIKE BIRDS

THE SHEATH-BILLS

(Family Chionidida)

On the extreme southern portions of South America and the adjacent islands, and on the farther Antarctic islands, are found four species of snow-white, Pigeonlike birds known as Sheath-bills, the name being derived from the remarkable saddle-shaped, horny sheath which encircles the base of the upper mandible and partially conceals the circular (holorhinal) nostrils.

There have been many differences of opinion as to the probable relationship of these birds, but after a careful and complete dissection of the Kerguelen Island form, Drs. Kidder and Coues conclude that they are”a connecting link, closing the narrow gap between the Plovers and Gulls of the present day,”and in their opinion”represent the survivors of an ancestral type from which both Gulls and Plovers have descended.”On the whole, however, their affinities seem to be rather more with the Chara-driidcB, and they are appropriately placed next to them.

As additional characters it may be mentioned that the Sheath-bills are four-toed birds, the anterior toes not being webbed, though there is a slight membrane between the base of the inner and outer toes; the tarsus is reticulated both before and behind and on the carpus there is a curious spur, the use of which is conjectural, as it does not appear to be employed in fighting. The Sheath-bills were formerly very rare in collections, which in a measure accounts for the uncertainty long existing regarding their relationship.

The four species are placed in two genera, the oldest known being Chionis, in which the face is bare and carunculated about the base of the bill. The oldest and best-known species (C. alba), which makes its home about the southern extremity of South America, attains a length of fifteen inches, and, as stated above, is snowy white throughout, with the bill and feet black or bluish dusky and the base of the mandibles yellowish. In 1904 an additional species (C. nasicomis) was described by Reichenow from Heard Island. In the second genus (Chi-onarchus) the face is bare in front but not below the eye and the caruncles are absent from the base of the bill. Of the two species in this genus we possess the most information concerning the Lesser Sheath-bill (C. minor) of Kerguelen Island and the Marion and Prince Edward islands.

Although called the lesser it is really larger than the first-mentioned species, being fifteen and one half inches long; the bill is black and the feet flesh-tinted, the plumage being uniformly pure white, and very soft and downy. When Kerguelen Island was visited by the Transit of Venus parties in 1874-1875, the Sheath-bill, or”White Paddy”of the whalers, was found to be abundant and so perfectly fearless as to be often taken in the hands.”It bears,”says Dr. Kidder,”a strong resemblance to the Pigeons in form and mode of flight; it is easily domesticated, remarkably fearless of man, dislikes water, cannot swim, is largely a vegetable feeder, and its usual note is a harsh croak.”On one occasion he observed a number on the rocks and walked toward them.”

They would scarcely get out of my way, seeming greatly interested in my movements, and when I sat on a stone, keeping perfectly still, the whole party, twelve in all, came up to examine the intruder. They walked all around me, coming almost within reach; others flying up from more distant rocks to join them, and finally stopping, almost in a semicircle, for a good stare.”

Their food he found to consist very largely of soft green seaweeds, which they stripped up with their bills, with occasional mussels and crustaceans; they also greedily devoured the eggs of various birds. Their own eggs, one to three in number, were placed in a carefully concealed nest of grasses in holes among or behind rocks. The remaining species (C. crozettensis) from the Crozette Islands is similar but smaller, with a smaller bill and darker feet.

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