Mr. T. KAZANO of the Tainan Museum, Formosa has sent me an example of
Tribura for identification. It was collected by him on Mt. Arisan, Central Formosa, October 5, 1936.
I have carefully compared it with a series of
Tribura luteoventris from Formosa and have come to the conclusion that it is no doubt a melanistic form of the present species in all respects. The dimensions of this specimen are as follows: total length 149mm. (measured by the collector in the flesh), wing 55.5mm. (56.5mm. in flat), tail 65.5mm., distance between central and lateralmost rectrices 30mm., tarsus 20mm., middle toe with claw 19.5mm., exposed culmen 11mm., entire culmen 13.5mm. Wing formula: the 1st primary 14mm. in length, the 2nd primary much shorter than the 10th, tip of wing forms by the 4th to the 6th primaries. Bill nearly black (very dark blackish brown) in skin, tarsus and toes "olive brown" of RIDGWAY and claws brownish horn colour in dry state.
The upper parts of the body including wings and tail almost "mummy brown"; the underparts including under wing-coverts also almost uniform "Saccardo's umber"; the ear-coverts with an indistinct pale shaft streaks as in ordinary examples (Pl. i, fig. 5).
Nestlings of the ordinary coloured phase represent the upper parts very much darker than those of the adult, uniform "sepia"; chin and throat greyish white with or without small dark brown spots like the cases of adult birds which vary individually, not according to the season! (Cf. Pl. i, figs. 1-3).
Chest and sides of body almost "Saccardo's umber, " centre of breast and abdomen as well as tips of under tail-coverts buffy white; under wing-coverts not growing, but edge of wing also buffy white as in that of adult bird (Pl. i, fig. 4).
From the above notes, it is clear that the melanistic example is no donbt a very rare one in this species.
Nineteen Russet Grass Warblers have been collected on Mt. Arisan and three examples on Mt. Taiheizan in Taihokusiu, Formosa. Mr. N. YAMADA has discovered nests, eggs and nestlings of the bird at altitude of 1200-3000m. on Mt. Arisan in 1935 and 1937. It breeds there from the middle of May to the end of June and the eggs and nestings were found on June 29, 1935, July 6, 1937, and July 10, 1935 (
cf. "Tori, " vol. ix, no. 45, pp. 445-446, pl. viii, fig. 10 (egg), text-fig. 133 (nest and eggs), Dec., 1937).
The date of collection of the skins of this species is March, April, June to October. It is a summer breeding resident on the mountains of central and north Formosa; and it has never been secured in winter months. Possibly it migrates in winter from the mountains to the plains or even reaching to the opposite continent. The problem of its winter haunt in Formosa is still unknown to science.
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