The stream, although maintaining a depth of 5 to 10 feet, at length became very narrow, and we were compelled, in order to proceed, to chop away the network of vegetation that overhung the water. Now and again it ran through open spaces covered with tall and matted grass, and then between banks a dozen feet high; but when we were forced to stop, unable to proceed further, the water was still brackish, although we had almost reached the hills in which it takes its source. The banks were frequented by herons, redshanks and other waders, and kingfishers (both _P. leucocephala_, with sandy head and body and blue wings, and the tiny _bengalensis_, the counterpart of our English bird). Several beautiful butterflies were seen, a rather common species, with velvety black wings, blotched with turquoise, constantly flitting up and down the course of the stream. We obtained good water in the harbour; slightly to the west of the little bay, a rocky hill makes an angle with a little beach of bright sand, and at the point of junction a path leads to the spring a few yards inland, where, in the jungle, the trickling water runs down a face of black rock, and collects in a stony basin. By forming a slight dam at the foot of the rock, any quantity can be collected. In the rocky hill just mentioned, we discovered several caves, which run inwards from mouths situated at the water's level. These are the homes of thousands of tiny leaf-nosed bats (_Hipposideros nicobarulæ_, sp. nov.), and immense numbers of the bird's-nest swift (_Collocalia linchii_). The largest of these caves is about 50 feet deep, and 20 feet high at the entrance; but at the back the accumulation of guano is so great that there is barely room to stand. As we entered with a lantern, our feet sinking ankle-deep into the soft chocolate-coloured floor, there was a continual rush of little bats and birds overhead as they sought to escape, and with a leafy branch we knocked over a number of each kind before going to the end. The rock at the back was covered with countless numbers of the shallow cup-shaped nests of saliva-gummed moss: so closely were they built, that in many cases one could not place a fingertip on the rock between them, and often they were constructed one on the side of the other. Nearly every one contained two comparatively large, white eggs, or ugly, unfledged nestlings. Fortunately for the birds, they are builders of the green variety of nest; for had these been white, they would not long have remained undisturbed by the Chinese. Swifts and bats--the one as graceful as the other is hideous--would seem queer neighbours, although there is a certain affinity between the two, for both enjoy the same food--flies and other insects--and obtain it on the wing without mutual interference; for the first hunt by day, and the others are nocturnal. In the cave, the swallows breed at the inner end, while the bats congregate near the mouth.