Data Zone
Justification of Red List category
This species qualifies as Endangered because it has a very small range and a small number of mature individuals (<2,500), being known only from Mt Talinis and the immediate area, where ongoing forest destruction and habitat degradation is leading to a continuing decline in the extent, area and quality of habitat, and the number of mature individuals, as evidenced from a decline in encounter rates since 1992.
Population justification
The population is estimated as 1,100-2,500 individuals, and 750-2,200 mature individuals. This estimate is calculated from 2017-2021 surveys for Z. nigrorum on Mt Talinis (Oracion et al. 2022). The surveys yielded an encounter rate of 0.034 birds per hour. This rate was transformed into a density per km2 using the stated survey design of 8 km total transect length per survey across a total of 175.8 hours (Oracion et al. 2022). The density calculation assumed a detection width of 25 m either side of the transect. The density was extrapolated to a minimum area of suitable habitat of 73 km2 and maximum area of 164 km2 (calculated by sRedList [2023] using data from Jung et al. [2020]). This method gave a population estimate of 1,091-2,451, rounded to 1,100-2,500. Not all of these are likely to be mature individuals although the proportion of mature individuals is likely high given this species' short generation length. The estimate is revised to 750-2,300 mature individuals.
Large areas of the species range have not been surveyed, or have not been surveyed consistently or thoroughly. This is reflected in the rates reported by Oracion et al. (2022) which range from 0/hour to 2.7/hour. Additionally, the exact habitat requirements and tolerance of the species for degraded habitats are unknown. Therefore, this range captures the uncertainty in the population, whilst accurately reflecting the consistent low reporting rates of the species (Oracion et al. 2022, eBird 2024).
Trend justification
In 1992, one survey on Mt. Talinis recorded 76 Negros Striped-babbler in a single day, a detection rate of 9.5 birds per hour (Brooks et al. 1992). The species was described as one of the most frequently recorded birds in the area (Brooks et al. 1992). Subsequent surveys have shown continuing decline in the detection rates of the species, from 9.5/hour to 1.8/hour in 2007, to 0.2/hour from surveys between 2017-2021 (Oracion et al. 2022). From the surveys collated by Oracion et al. (2022), the highest number of birds recorded in a single day was 12. If the Brooks et al. (1992) estimate was an anomaly, the detection rates from 2007-2021 still show a clear decline in detection rates (Oracion et al. 2022).Given the continuing degradation of habitat across the species' range, these reporting rates are very likely representative of a continuing decline in the number of mature individuals.
Zosterornis nigrorum is endemic to Negros in the Philippines, where it is known from the vicinity of Mt Talinis in the south (BirdLife International 2001), including within Balinsasayao Twin Lakes National Park north of Mt Talinis. The species may also occur in Mt Canlaon in the north, but has not been recorded here since 2015 (Pios et al. 2016, eBird 2024). The species has also been recorded south of Mt Talinis at Mt Hapon-haponon (Oracion et al. 2007, Bucol 2009) and in the vicinity of Mt Mantiquil (eBird 2024), but has not been recorded since 2009 and 2015 respectively.
Z. nigrorum primarily inhabits montane forest at 900-1,600 m, and most consistently above 1,000 m (Collar and Robson 2020, Oracion et al. 2022). The species has also been recorded in degraded habitats where there is still sufficient understory and canopy density (Brooks et al. 1992, Oracion et al. 2022), including banana cultivations with remnant secondary and mature forest (Oracion et al. 2022). The species also occupies a vertical range as high as 60-65m (Oracion et al. 2022). The species is consistently observed in mixed flocks and feeds in the understory on small fruits and insects (Brooks et al. 1992, Oracion et al. 2022).
Agricultural and logging activities on Negros within the range of Z. nigrorum are ongoing. These activities were reported to have reached 1,250m on Mt. Talinis as of 1992 (Brooks et al. 1992). The area has seen a continuing rate of deforestation, with a 1.1% loss of forest cover from 2012-2022 (Global Forest Watch 2024, based on data from Hanson et al. [2013] and methods disclosed therein).
In conjunction with general habitat loss, the species is also undergoing population declines within suitable habitat as estimated from a large reduction in reporting numbers (Oracion et al. 2022). These declines are likely due to a combination of habitat degradation from logging activities and slash-and-burn agriculture (Brooks et al. 1992, Oracion et al. 2022). Degradation from human activities is apparent from a 10km2 reduction in suitable habitat within the species range between 2010 and 2020 (calculated by sRedList [2023] using data from Jung et al. [2020]), a low forest integrity score (Global Forest Watch 2024 using data from Grantham et al. [2020]), and an increase in the Human Modification Index across the range between 1990 and 2015 (calculated by sRedList [2023] using data from Theobold et al. [2020]). There are also likely other undetermined threats impacting the species, as evidenced from decrease in encounter rates since 1992, and further from 2007 until 2021 (Oracion et al. 2022). For example, climate change may also be having an unknown impact.
Conservation Actions Underway
The Mt Talinis/Twin Lakes area has been proposed for conservation funding and environmental awareness campaigns have been conducted near Mt Talinis itself (BirdLife International 2001).
14·5–15 cm. Forecrown and supercilium are black, rest of crown, neck side and upperparts olive; upperwing and tail dark greyish-brown, tertials and secondaries with whitish inner fringes (invisible on closed wing); lores whitish, cheek and frontal ear-coverts whitish with blackish flecks, rear ear-coverts olive with blackish flecks, submoustachial area white basally, black distally; chin and throat whitish, shading to yellowish on breast to belly, with narrow blackish shaft streaks on breast and broader, softer-edged, more greyish-olive streaks on belly and vent, olive-grey flanks and thighs; iris colour undocumented, believed dull reddish; white orbital skin; bill black; legs dark grey. Sexes similar. Juvenile apparently unrecorded.
Similar spp.: Possibly confusable with other small passerines with streaked underparts (e.g. Muscicapa flycatchers), but distinguishable by combination of behaviour and dark mask. Differs from very similar Z. latistriatus in having black extending from forehead over eye, no obvious “tramlines” (moustachial and malar lines) in upper submoustachial area but lower submoustachial area black and pronounced, streaking below much thinner and olive-green, rather than blackish (also, tail reportedly more reddish, but this not apparent on skins).
Voice: Song a loud pure whistle (sometimes delivered as subdued version), “pli-hi pli-hy pli-hi pli-hy” (or “pli-plie”), the first and third couplets rising and second and fourth falling, or “plea-he, plea-hü, plea-he, plea-hü”; a single burst also described as “tu-tu tutu soo”. Contact call a soft continuous “tsip, tsip…” or short sharp “tzi”, sometimes becoming a trill; also a high-pitched “weeet” and a double note.
Hints: Often encountered in groups, including mixed-species foraging flocks.
Text account compilers
Richardson, L.
Contributors
Bucol, A., Taylor, J., Benstead, P. & Gilroy, J.
Recommended citation
BirdLife International (2024) Species factsheet: Negros Striped Babbler Zosterornis nigrorum. Downloaded from
https://datazone.birdlife.org/species/factsheet/negros-striped-babbler-zosterornis-nigrorum on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 23/12/2024.