The question as to the true cause of the difference in the nests has not yet been satisfactorily solved. Some allege that the red and black nests are simply white ones deteriorated by not having been collected in due season. I myself incline to agree with the natives that the nests are formed by different birds, for the fact that, in one set of caves, black nests are always found together in one part, and white ones in another, though both are collected with equal care and punctuality, seems almost inexplicable under the first theory. It is true that the different kinds of nests are not found in the same season, and it is just possible that the red and black nests may be the second efforts at building made by the swifts after the collectors have disturbed them by gathering their first, white ones. In the inferior nests, feathers are found _mixed up_ with the gelatinous matter forming the walls, as though the glands were unable to secrete a sufficient quantity of material, and the bird had to eke it out with its own feathers. In the substance of the white nests no feathers are found. Then, again, it is sometimes found in the case of two distinct caves, situated at no great distance apart, that the one yields almost entirely white nests, and the other nearly all red, or black ones, though the collections are made with equal regularity in each. The natives, as I have said, seem to think that there are two kinds of birds, and the Hon. R. ABERCROMBY reports that, when he visited Gomanton, they shewed him eggs of different size and explained that one was laid by the white-nest bird and the other by the black-nest builder. Sir HUGH LOW, in his work on Sarawak, published in 1848, asserts that there are "two different and quite dissimilar kinds of birds, though both are swallows" (he should have said swifts), and that the one which produces the white nest is larger and of more lively colours, with a white belly, and is found on the sea-coast, while the other is smaller and darker and found more in the interior. He admits, however, that though he had opportunities of observing the former, he had not been able to procure a specimen. The question is one which should be easily settled on the spot, and I recommend it to the consideration of the authorities of the British North Borneo Museum, which has been established at Sandakan. The annual value of the nests of Gomanton, when properly collected, has been reckoned at $23,000, but I consider this an excessive estimate. My friend Mr. A. COOK, the Treasurer of the Territory, to whose zeal and perseverance the Company owes much, has arranged with the Buludupih tribe to collect these nests on payment to the Government of a royalty of $7,500 per annum, which is in addition to the export duty at the rate of 10% _ad valorem_ paid by the Chinese exporters.