Bicol Ground-Warbler Robsonius sorsogonensis Scientific name definitions

20–22 cm; 57–65 g. Adult has forehead greyish olive, shading on crown to olive, all with faint dark scales; mantle and upper back olive with faint narrow dark scales, becoming uniform brown on lower back, paler on rump, where white tips of feathers form semi-concealed bar, uppertail-coverts dark rufescent-brown, tail dark brown; greater and median upperwing-coverts black, broadly fringed brown and tipped white, rest of upperwing-coverts greyish olive-brown, a few near bend of wing tipped white, primary-coverts black with white tips, flight-feathers broadly edged brown, with bold white tips on outer two and indistinct tip on third; lores and narrow supercilium to above eye white, cheek and ear-coverts grey, finely streaked white, submoustachial stripe white, narrow malar streak blackish; chin to upper breast white, neck and breast sides and middle to lower breast grey, belly white, long fluffy feathering on flanks dull rusty brown, undertail-coverts dark red-brown; iris brown; bill blackish brown, basal half of lower mandible grey; legs light brown. Differs from similar R. rabori in having crown much less rusty, head side greyish with white flecks, chin to upper breast white, grey breastband shading to white belly, much less dark scaling above. Sexes similar. Juvenile has buffier throat and cheeks with less obvious dark tips on submoustachial area, weakly developed grey breastband, all-chestnut belly and flanks, obscured (grey-buff) tips of wing-coverts and outer primaries, pale lower mandible.

C & S Luzon and Catanduanes, in NC Philippine Is.

Song  a very high, thin, high-pitched “tit’tsu—tsuuuu-tsiiiiii” (third and fourth notes higher, fourth rising towards end), also “tssuit’swiieeii”, “tssuu’sit’suuiiee”, “tssiiuu’sweeiieet” or “tit-tsuee-swiieet”, lasting 1·2–1·9 seconds and repeated every 2–7 seconds; similar in pitch and quality to that of R. rabori, but apparently somewhat shorter and simpler in structure. Calls as yet undescribed.

Not globally threatened. Currently considered Near Threatened. Restricted-range species: present in Luzon EBA. Status difficult to determine owing to secretive habits. Considered uncommon. As with R. rabori, numbers may be higher than is suggested by field observations, although habitat loss within its range has been, and continues to be, extensive. Previously considered Vulnerable, but now thought to occur at more than ten localities (2 Hosner, P.A., Boggess, N.C., Alviola, P., Sánchez-González, L.A., Oliveros, C.H., Urriza, R. and Moyle, R.G. (2013). Phylogeography of the Robsonius ground-warblers (Passeriformes: Locustellidae) reveals an undescribed species from northeastern Luzon, Philippines. Condor 115(3): 630–639. Close ) and to be tolerant of forest degradation, perhaps even preferring scrubby, bamboo-dominated forest; consequently downlisted to Near Threatened in 2015. Present in Quezon and Mount Isarog National Parks.