274 Mr. R. Swinhoe on Formosan Ornithology . 
its tribe, it feeds on freshwater insects, Crustacea, and Mollusca. 
I met with it on one of my rambles into the hills. It was 
perched on a large slab of rock that stood in a running stream. 
It kept throwing up its tail like a Wren, and, hopping to the 
edge of the stone, dashed into the water; in a few seconds it 
reappeared at the surface and regained the rock. Till then I 
was not quite sure what bird it was ; there was no longer any 
mistake. My time was short, and I could watch no longer; so I 
secured my specimen and went my way. It was a likely place and 
season for its nest, but in my hurried search I could not detect it. 
33. Petrocincla manilensis (Bodd.). 
In Formosa you find this species as it is generally known, with 
blue upper plumage and breast and red belly. In all my nume¬ 
rous specimens the colours are always uniform. But in Amoy the 
red belly is by no means constant; I have several skins entirely 
blue, and others again with all proportions of red and blue. This, 
however, does not appear to be the case in the Formosan bird; so 
we will not here discuss the question of the validity of the species. 
The female retains the mottled plumage through life; but the 
young male in the first autumnal moult shows a good deal of 
blue on the back and throat, and red on the lower parts: the 
plumage becomes more defined in the following spring; but the 
mottles do not entirely disappear till the close of the second year, 
and often not then. 
Length. Wing. Tail. 
Male . .8^ in. 5^ in. 3^ in. 
Female.8J 3j% 
Both sexes vary somewhat in size, as also in the length of the 
wing. My measurements are from full-sized examples. 
This bird is partial to rocky hills near the sea. Its song is 
very sweet, and is often uttered on the wing. It builds its nest 
in the hollows and clefts of rocks and walls, adapting it to the 
shape of the chosen locality, and constructing it of fine flexible 
twigs, lined with fine grass, wool, and occasionally a few feathers. 
These are loosely put together, without much art. It lays from 
three to five pale greenish-blue eggs. In autumn, after the first 
moult, the young leave the hills and frequent the housetops of 
