(811) Tribura luteoventris Hodgs.
THE BROWN BUSH-WARBLER.
Tribura luteoventris, Fauna B. I., Birds, 2nd ed. vol. ii, p. 406.
This species of Tribura has a wider range than either of the preceding species, being found from Nepal and Sikkim, throughout the lower Outer Himalayas, to Eastern Assam, the Chin and Kachin Hills to Annam and, according to Stresemann, as far East as Szetchuan. It is very common in suitable places in the hills South of Assam, being exceptionally numerous in the Khasia Hills between 4,000 and 6,000 feet. In Sikkim it should be noted that Stevens records it up to 9,000 feet.
This is much more of a forest bird than either of the two pre¬ceding birds and it is also one of the few which habitually haunts. Pine forests, so long as these are fairly open and have enough undergrowth to conceal it as it skulks about. In many of the Khasia Pine forests there is a very dense undergrowth of Daphne- bushes, and with these there is mixed a certain amount of bracken and grass—the more open the forest the more these last two flourish. In other Pine forests numerous ravines break up the ground, and in these but few Pine-trees grow, their place being taken by other deciduous trees and an undergrowth, sometimes quite thick, of bracken, brambles of all kinds and low and tall bushes. Both these types of undergrowth are favourite breeding resorts of the Brown Bush-Warbler, though many birds also breed on the open hill-sides between the forests, where there is much bracken, bush and grass growing between the quite open grass-lands and the edge of the forest.
Out of the hundreds of nests I have taken or examined I have seen only two or three built actually on the ground under the shelter of a tuft of coarse grass or at the roots of a Daphne-bush, among weeds. Most nests are built well inside Daphne-bushes or in tangles of bramble, weeds or coarse grass a few inches to a couple of feet from the ground. Higher than this is not so usual, though I have seen nests in both bushes and Raspberry-brambles as high as 4 feet from the ground.
The nests are of two kinds. The great majority are deep cups, the depth exceeding the breadth ; probably an average-sized nest would be about 3 inches across the top and 4 to 5 inches in depth, while others exceed this by a full half inch either way ; yet others are decidedly smaller. The top of the nest is usually not quite the widest part, the lips being drawn in a little.
The dome-shaped nests average about 3.1/4 inches in diameter by about 5 inches from top to bottom, the egg-cavity being roughly about 2.1/4 to 2.1/2 inches each way.
Both kinds of nests are made entirely of grass-blades and strips of grass, firmly but not very tidily wound together, the material used being generally old and often considerably torn and broken. Inside most nests, but by no means always, finer blades and grass stems are used, though these can hardly be said to form a lining. I have seen feathers placed inside sometimes. Of these, one single feather may be stuck casually into the nest, near the top just as likely as near the bottom, or a few, half a dozen at the most, make an apology for a lining. Very rarely there is a real, though meagre, lining of grass-stems, rather finer than the rest of the materials.
May is undoubtedly the month in which most eggs are laid but, probably, many birds have two broods, as in July there seems to be another burst of egg-laying. I have taken eggs at all dates between the 19th of April and the end of July.
The eggs are like those of the two species already dealt with but, as a series, are decidedly darker, and are far more often well capped or zoned. I have two or three clutches in which the markings all coalesce to form unicoloured caps in one or more eggs. In a few eggs, also, the markings are larger—blotches rather than specks or spots.
Two hundred eggs average 18.2 x 14.3 mm. : maxima 19.9 x 14.9 and 19.0 x 15.2 mm. ; minima 16.9 x 14.5 and 17.3 x 13.3 mm.
Both sexes incubate, but the female far more than the male, the birds trapped on the nest, being, in four cases out of five, females. The female performs most of the building operations also, though the male bird brings a certain amount of material to the nest.
Incubation takes twelve or thirteen days, probably the former, though I have never been able to fix it exactly.
811. Tribura luteoventris
(811) Tribura luteoventris Hodgs.