The Solomon Islands and Their Natives

by H. B. Guppy

The handsome ground-pigeon, known as the Nicobar pigeon (Geophilus nicobaricus), is commonly observed in the wooded islets on the coral reefs of the Solomon Group. As I have remarked on [page 293], this bird is probably instrumental in transporting from one locality to another the small hard seeds and fruits which the common fruit-pigeon (Carpophaga) refuses. That it is able to crack such hard seeds as those of the leguminous plant Adenanthera pavonina,[457] is shown by the fact that I have found these seeds cracked in the cavity of the gizzard, which is in its structure and mechanism a veritable pair of nutcrackers. In this bird the muscular stomach or gizzard is of a surprising thickness, and is provided with a very singular mechanical contrivance to assist its crushing power. As shown in the accompanying [diagram], it is composed of two muscular halves, each having a maximum thickness of five-eighths of an inch and united with each other in front and behind by a stout distensible membrane, which is the proper wall of the organ. Developed in the horny epithelial lining membrane there are two cartilaginous bodies of hemispherical shape, one in each muscular segment of the gizzard, which measure about one-third of an inch in thickness and three-fourths of an inch in diameter. The outer or convex surface of each cartilaginous body fits into a cup-shaped cavity which is lined by a semi-cartilaginous membrane, the whole constituting a “ball-and-socket” joint with well lubricated surfaces. The two surfaces of this pseudo-articulation are capable of easy movement on each other, being retained in close apposition by the attachment to the subjacent tissues of the horny epithelial lining membrane in which the cartilaginous body is developed. The inner or free surface of each hemispherical body, that which looks into the gizzard cavity, is somewhat concave, and projects a little above the surface of the lining membrane; it is much harder than the opposite convex side of the cartilage and has almost the consistence of bone, the arrangement of the cells into densely packed rows with but little intervening matrix indicating an approach towards ossification.

[457] The Kuara tree of India, of whose hard seeds necklaces are made.

The firm consistence of these hemispherical cartilages combined with the mechanism of a moveable articulation must greatly assist the already powerful muscular walls of the gizzard; but there is an additional factor in the crushing power in the constant presence of a small quartz pebble, usually about half-an-inch across. With such a apparatus, I can well conceive that very hard seeds and nuts may be broken, as in the case of the seeds of Adenanthera pavonina already alluded to. The Nicobar pigeon is in fact possessed of a nut-cracking mechanism in its gizzard, by which nuts like those of our hazel tree would be cracked with comparative ease.

With reference to the small quartz pebbles found in the gizzards of these birds, I should remark that there is usually only one present, and that it varies in weight between 30 and 60 grains. I was sometimes able to say where the pigeon had obtained its pebble. Thus, in Faro Island the bird often selects one of the bipyramidal quartz crystals, which occur in quantities in the beds of the streams in the northern part of the island, where they have been washed out of the quartz-porphyry of the district. In other instances the pebble seems to have been originally a small fragment of chalcedonic quartz, such as composes some of the flakes and worked flints that are found in the soil which has been disturbed for cultivation. Sometimes the pebble is of greasy quartz; and now and then in the absence of quartz the bird has chosen a pebble of some hard volcanic rock. It is a singular circumstance that although these pigeons frequent coral islets where they can easily find hard pebbles of coral-rock, they prefer the quartz pebbles which are of comparatively rare occurrence. I never found any calcareous pebble in their gizzards, and was often at a loss to explain how the bird was able to ascertain for itself the different degree of hardness between the two pebbles, when the quartz was of the dull white variety. . . . I learn from a recent work on New Guinea by the missionaries, Messrs. Chalmers and Gill, that inside the gizzard of each Goura pigeon there is a good-sized pebble much prized by the natives as a charm against spear-thrusts and club blows.[458] The Goura pigeon resembles the Nicobar pigeon in habits; and I think it probable that its gizzard will be found to present a similar structure and mechanism for cracking nuts and hard seeds. The common fruit pigeons (Carpophaga) of the Solomon Islands, living as they do on soft fleshy fruits, and rejecting the hard seeds and kernels, have no peculiar structure of the gizzard, the walls of which are comparatively thin, and are thrown into permanent rugæ somewhat warty oh the surface.

[458] “Work and Adventure in New Guinea” (p. 317): London, 1885.

One of the most familiar birds in these islands is the “bush-hen,” which belongs to the family of the mound-builders (Megapodiidæ). They bury their eggs in the sand at a depth of between three and four feet. On one occasion in the island of Faro, Lieutenant Heming and his party found eight eggs, in different stages of hatching, thus buried: they were scattered about in the sand; and according to the account of the natives only one egg was laid by each bird. The eggs are sometimes found on the surface of the sand. The young birds are able to fly short distances soon after they are hatched. One that was brought on board astonished us all by flying some thirty or forty yards from the ship and then returning to the rigging.

The account recently published by Mr. H. Pryer of his visit to the birds’ nest caves of Borneo[459] has opened up the discussion as to the nature of the substance of which the edible bird’s nest is composed. Many and varied have been the surmises as to the source of this material; but nearly all of them have been based on mere speculation, and have been relegated to the limbo of sea-tales. Amongst the earlier explanations, I may allude to those which have been given by early writers. The swiftlets (Collocalia), which build their nests in this extraordinary fashion, were considered to gather a gelatinous material from the ocean-foam, or from the bodies of holothurians, or from the skin of the sun-fish. The Chinese fishermen assured Kæmpfer that their nests were composed of the flesh of the great poulpe. A more probable explanation, however, was found by Rumphius in the occurrence on the sea-coasts of a soft almost cartilaginous plant which he with confidence asserted was the material from which these swiftlets constructed their nests; but subsequently this naturalist inclined to the opinion that the substance of which the edible birds’ nests are composed is merely a secretionary product. In these two views of Rumphius we have the two sides of the controversy very much as it at present stands. On the one hand, there are those who hold that this substance is a secretionary product: on the other hand, the opinion is held that the nest is constructed of a vegetable matter, usually resulting from the growth of a microscopic alga, which is found in the caves and on the faces of the cliffs where the nests occur. All the weight of experiment and of actual observation tends to negative the view of the vegetable origin of this substance. Sir Everard Home in 1817 declared his opinion that certain peculiar gastric glands, which he found in one of these birds, secreted the mucus of which the nest was formed. In 1859, Dr. Bernstein[460], after having carefully studied the habits of the birds in question, came to the conclusion that their nests are formed from the secretion of certain salivary glands which are abnormally developed during the nest-building season. M. Trécul, who held the same opinion, showed that the bird constructs its nest by means of a mucus which flows abundantly from its beak at the pairing time.[461] This last view is strongly supported by Mr. Layard, who unhesitatingly pronounces his opinion that these swiftlets build their nests from the secretionary products of their own salivary glands.[462] However, when Mr. Pryer visited in March, 1884, the birds’ nest caves in British North Borneo, he considered that he had found the source of the material of which the nests were composed in the occurrence of a “fungoid growth,” which incrusted the rock in damp places, and which, when fresh, resembled half-melted gum tragacanth. Without at present expressing an opinion as to the validity of the inference Mr. Pryer drew from his observations in these caves, I may observe that the “fungoid growth” has been determined by Mr. George Murray,[463] of the Botanical Department of the British Museum, to be the result of the growth of a microscopic alga, a species, probably new, of Glœocapsa; whilst the edible nests from these caves, according to a chemical and microscopical examination made by Mr. J. R. Green,[464] have been shown to be formed in the great mass of mucin, which is the chief constituent of the mucous secretions of animals. After examining various specimens of edible nests from other localities, Mr. Green subsequently confirmed the results of his first experiments. The nest-substance, as he unhesitatingly states, is composed of mucin, or of a body closely related to it.[465] So far, therefore, there would appear to be but little evidence to support the view of Mr. Pryer that the species of alga, which he found incrusting the rock in the vicinity of the Borneo caves, supplied the material for the construction of the nests of the swiftlets. However, before proceeding to state my own opinion on the matter, I will refer briefly to my observations in the Solomon Islands relating to this question.

[459] Proceedings of the Zoological Society for 1884: p. 532.