MIGRATION OF THE PACIFIC PLOVER TO AND FROM

THE HAWAIIAN ISLANDS.1

By HENRY W. HENSHAW.

Since primitive times the phenomenon of bird migration has excited peculiar interest, and although much of the mystery formerly attaching to it has been dispelled by the prosaic facts brought to light by modern investigations, it still presents enigmas to stimulate the imagination and invite study. How birds migrate is now beginning to be understood, and the present practice of tabulating dates of arrival and departure and collating the facts gathered by numerous observers in different parts of the country is likely ere long to give us the solution of many as yet unsolved problems. Why birds migrate is quite another question, likely to resist satisfactory solution for some time to come for, were there no other reason, from the very nature of the case we can have comparatively few facts to guide us, and speculation must largely take the place of deduction.

When we consider the number of miles traveled, the widely different character of the regions chosen for summer and winter abodes, and the perils necessarily attending the passage between them, the migration of no other of our birds appears so wonderful as that of the golden plover. In part the migration route of the eastern form of the golden plover (Charadrius dominicus) is well understood, and those interested in the subject are referred to a suggestive paper by Austin H. Clarke on the probable method by which the bird is guided safely across the Atlantic from Nova Scotia to South America. In the present paper will be presented such facts in regard to the migration of the Pacific plover (Charadrius dominicus fulvus) as the author was able to gather during his stay in the Hawaiian Islands from 1894 to 1904-together with certain deductions therefrom.

1 Reprinted by permission, after author's revision, from The Auk, a quarterly journal of ornithology, Cambridge, Mass., vol. 27, No. 3, July, 1910.

2 Auk, pp. 134-140, 1905.

97578°

-SM 1910

-35

545

Isolation of the Hawaiian Islands.-It may be premised that no other part of the earth's surface is so far distant from continental areas as the Hawaiian Archipelago. The islands are about 2,000 miles from the coast of California on the east; about the same distance from the Aleutians on the north and the Marquesas Group on the south; and not much farther from Japan, reckoning from the outermost of the chain of low islands and reefs which stretches from Hawaii some 1,700 miles toward the Asiatic coast. It is important to note, however, that, assuming the availability of these islands as stepping-stones for birds, there would still be an interval of more than 2,000 miles between the most northwestern of the chain and Japan. Hence, if we reject as untenable the theory of a sunken southern continent, of which the Hawaiian Archipelago is the northernmost and now the only visible remains, the original introduction into Hawaii of its mammals, birds, insects, and plants presented greater difficulties than were presented to the fauna and flora of any other part of the world.

So remote and isolated have these islands been since their formation, and so few and uncertain nature's carrying agencies-the birds, the winds, and the ocean currents-that after the islands were thrust up out of the sea ages must have elapsed before they received the parent stocks of the many and diverse forms of plant and animal life peculiar to them.

That the difficulties of stocking the archipelago with life, great as they must have been, were not insurmountable is proved by the fact that enough waifs found their way to the islands to clothe them with verdure and stock them with animal life. As a result of the competitive struggle which followed, upward of 900 species of plants, numerous insects, including many distinct genera, seven species of lizards, more than 50 species of birds, and at least two mammals, finally made good their foothold on the islands and flourished, some more, some less, according to their nature and adaptability.

Avifauna of the Hawaiian Islands.-Among other inhabitants of the islands are some 45 species of passerine birds, one hawk, an owl, a mud hen, a gallinule, a stilt, a duck, a goose, and a few others. All of these I pass by for the moment and come to certain migrants from North America which regularly journey between the islands and the continent, both spring and fall. Four of these migrate in great numbers, viz, golden plover, turnstone, wandering tatler, and bristle-thighed curlew; the shoveler duck and pintail also visit the islands in considerable numbers. In addition to these are perhaps a dozen other ducks and geese whose occurrence in the islands is more or less casual, and the same remark applies to a dozen or 15 wading birds. Altogether, including the regular migrants, the

casuals, and the accidentals, the visiting birds make quite a respectable winged army.

Islands accidentally discovered by present migrants.—It is not supposable that birds ever put to sea to seek unknown lands by a hitherto untraveled route. We know that millions of birds of many species are annually or semiannually driven out to sea by storms, especially species that migrate near the seacoast. Many, perhaps most, of these storm-driven waifs never see land again, but become wing weary and find watery graves. Some few, however, reach safe havens in oceanic islands, and in this way, no doubt, such islands have received their bird colonists.

That the golden plover, like the other migrants from the North American coast, discovered Hawaii accidentally is hardly open to doubt. I see no necessity for presupposing the existence of sunken continents or of ancient continental extensions to account for the presence on the islands of the plover and other North American birds, like the night heron, gallinule, and coot. The presence there of the weak-winged passerines is another matter, and it must be admitted that proof of the existence of an ancient continent, stretching from the islands southward toward Australia, would simplify a very difficult problem. So far, however, as our North American birds are concerned, it need be assumed only that long ago some thousands of Pacific plover and other species, when following the usual southward migration route along the Asiatic coast in fall, were accidentally driven to sea, and that a greater or less number were able to maintain themselves on the wing long enough to make a lucky landfall of the low islands to the northwest of Hawaii. The flight from Japan to the nearest island eastward would involve a flight about as prolonged as that from the Aleutian Archipelago to Hawaii, or some 2,000 miles. The chain of low islets once gained, it would be but a question of time for migrants, step by step, to reach the larger islands of Hawaii, 1,700 miles or so to the eastward. After wintering, a sufficient number may have essayed the flight back across the ocean to the Asiatic coast the following spring, and then northward to their Siberian breeding grounds with their Asiatic fellows. Having once discovered the islands and learned their suitability as winter quarters, they would no doubt return over the same route, and thus in time establish a regular fly line or migration route from the Asiatic mainland to the islands. Later, as the position of the islands became better known, the part-land, part-water route would naturally be exchanged for a shorter all-water route. It is possiblę, however, that the old Asiatic route has never been wholly abandoned and that it is still favored by a certain number of the island migrants; for plover, turnstones, curlew, and tatlers have been observed on Laysan, about 600 miles northwest of Hawaii, late in May. These

birds were probably about to migrate across the ocean, but it is, of course, impossible to tell whether they were headed directly for America or for America via Asia.

Absence of fog.-The original discovery of the Hawaiian Islands by birds was undoubtedly greatly facilitated by the fact that, although fog is common on the mountains at altitudes of 5,000 feet and upward, it never occurs at sea level; and as its absence favored the original avian discoverers, so it continues to favor annual migrants.

Date of discovery of the islands by American migrants.-As to the length of time the Pacific golden plover and its fellow migrants have been visiting the Hawaiian Islands, or when they first discovered the group, it were idle to speculate. Their arrival probably antedated by thousands of years that of the natives, which is supposed to date back only some 20 centuries. Certain of the bird colonists from America, like the owl, night heron, gallinule, and coot, have resided in the islands so short a time that they have changed very little from their American ancestry. Others, like the hawk, stilt, and goose, have changed more, and hence presumably have been residents of Hawaii a longer time. Changes of color, proportion, and size, however, be they great or small, can not be used as time measures, except in the vaguest way, since practically next to nothing is known of the length of time they require. We are perhaps justified in concluding that none of the above species have changed sufficiently to call for isolation from their American ancestors for periods to be reckoned by geologic intervals rather than by thousands of years.

Spring migration of plover.-The impulse to migrate in spring is by no means simultaneous among all the plover that winter in the islands or that winter on any one island, nor, apparently, is it the rule for large bodies of plover to migrate together. The plover and turnstones, probably often in mixed companies, begin to leave for the north early in April, and the migration continues till at least the latter part of May (probably even later), being dependent, apparently, on the state of preparedness or the inclination of individual birds.

When the time to migrate comes, small parties, from a dozen or even less, to flocks of 200 or more, strike boldly out to the northward, apparently without hesitancy or doubt of the result. Mr. Haswell, of Papaikou, which is on the coast about 15 miles north of Hilo, soon after daybreak during the early days of April, 1900, saw several flocks rise to a great height and, after widely circling about a few times as if to orient themselves, finally disappear in a northerly direction.

It is probable, however, that day migration is not the rule with plover and other shore birds. Apparently it is more usual for the flocks to feed by day and leave just before nightfall, as do many other birds in different parts of the world. Mr. R. C. L. Perkins states that several times he "witnessed these departures, always late in the afternoon or just before dark." He adds:

When about to return to the north, the plover frequently assemble in very large flocks, and before setting out on their journey rise to an enormous height in the air, even beyond the range of sight. I have once seen two such flocks start from the same point, the one following the other after an hour's interval.[Fauna Hawaiiensis, Vol. I, pt. iv, p. 449, 1903.]

It is interesting to note that plover are occasionally sighted from passing ships. Naturally they attract little attention and never are recorded in the ship's log. I found one ship captain, however, who remembered to have seen a flock of plover passing north in spring. The date was uncertain, but the ship was about midway between San Francisco and Hawaii, and the plover were steering a course which would carry them to the neighborhood of the Aleutians.

Where data are so scarce and difficult to obtain it is worth noting, as bearing on the season and course of the spring migration of island birds, that Townsend captured a Pacific plover, which boarded the Albatross May 19, 1890, when 600 miles south of Kadiak. This bird was probably an island migrant nearing the end of its long flight. Elliott, also, speaking of the turnstone, states that he "met with it at sea 700 miles from the nearest land, flying northwest toward the Aleutian Islands, my ship being 800 miles west of the Straits of Fuca."

Physical condition of spring migrants.-During the last two months of their stay in the islands both the migrating plover and turnstones get very fat, and it is probable that individuals that are not in good condition do not attempt the flight, or if they do, do not survive the attempt. Toward April most plover seem to be in full breeding plumage, and I feel sure that none of the birds assuming the breeding dress remain behind, unless sick or wounded. There is, however, a small contingent, both of plover and turnstones, that summer in the islands, and these appear to consist wholly of immature individuals, which, as a rule, are thin and not in good trim.

Speed of migrating plover.-The migration of plover over a wide ocean involves two factors: (1) Ability to go without food for the time necessarily consumed in the flight. (2) Ability to make the journey without resting and yet not overtax the physical powers. As stated above, apparently all the migrating birds in spring are in good order, and some of them, especially the males, are exceedingly fat. They are thus in condition to exert their utmost powers for a considerable period and to do without food. I know of no actual