Justification of Red List category
This species qualifies as Vulnerable because it is restricted to low-lying forest in a region where this habitat-type is being cleared and degraded at a catastrophic rate, such that rapid and continuing population declines are suspected.
The population size is preliminarily estimated to fall into the band 10,000-19,999 mature individuals. This equates to 15,000-29,999 individuals in total, rounded here to 15,000-30,000 individuals.
Recent data on the population size and trend are lacking, but habitat conversion continues at a catastrophic rate across the region, particularly within the specialised habitats occupied by this species, suggesting a rapid and continuing decline.
Setornis criniger is confined to Borneo (including Sabah and Sarawak, Malaysia, Brunei, and Kalimantan, Indonesia) and the Indonesian islands of Sumatra and Bangka (BirdLife International 2001). It is locally common on Borneo, perhaps rarer in the north and appears always to have been relatively rare and restricted in range on Sumatra. On both islands it is likely to be in steep decline owing to the destruction of its habitat.
It is strongly associated with nutrient-poor vegetation on acid soils. These include peatswamp (lowland evergreen forest characterised by low tree species diversity and strong adaptation to a fluctuating water-table and heath forest (kerangas, dense, low forest of thin-boled, small-leaved and often sclerophyllous trees). It has also been recorded in abandoned rubber plantations, ridge-top heath forest (to 1,000 m), sometimes tolerating secondary forest, but generally avoiding dryland primary forest.
Peatswamp forest on Borneo and Sumatra is now under extreme pressure through logging and agricultural, industrial and residential development, particularly oil palm plantation agriculture (G. Davidson in litt. 2007, B. van Balen in litt. 2012). It is rendered more vulnerable by its restriction to coastal lowlands. In addition, recent forest-fires have destroyed vast swathes of primary peatswamp vegetation. Even in protected areas, such as Tanjung Puting National Park, industrial-scale illegal logging is proceeding at sufficient pace that most peatswamp forest is likely to disappear in the next decade.
Conservation Actions Underway
It occurs in the Klias Forest Reserve, Sabah (F. Lambert in litt. 2002), Similajau National Park and Samunsam Wildlife Sanctuary (Sarawak), Gunung Palung and Tanjung Puting National Parks (Kalimantan) and Padang-Sugihan Wildlife Reserve (Sumatra). There is an old record and several unconfirmed recent reports from Kayan-Mentarang National Park (East Kalimantan), whilst there is an old unconfirmed report from Danu Sentarum National Park (West Kalimantan), and a number of confirmed records in 2008-2009 from an area immediately to the south of the park (per B. van Balen in litt. 2012). Nevertheless, only c.7% of remaining peatswamp-forest is under actual or proposed protection, whilst almost all protected areas containing this habitat continue to be threatened by logging, drainage and development. Attempts have been made to slow the conversion of peatswamp forest on Borneo through legislation and efforts by various organisations (B. van Balen in litt. 2012).
19-20 cm. Drab, forest-dwelling bulbul. Warm brown crown, rest of upperparts mid-brown. Distinctive face pattern with whitish supercilium, blackish eye-stripe and moustachial divided by greyish cheeks. Pale whitish-buff underparts, greyer on flanks. Brown outer tail feathers broadly tipped white. Strong and hook-tipped bill. Similar spp. Puff-backed Bulbul Pycnonotus eutilotus also has white-tipped tail feathers, but is warmer brown, usually has visible crest and red eyes, and lacks supercilium and eye-stripe. Voice Relatively quiet, but gives loud, harsh crruk.
Text account compilers
Benstead, P., Gilroy, J., Taylor, J.
Davidson, G., van Balen, B., Lambert, F.
BirdLife International (2023) Species factsheet: Setornis criniger. Downloaded from http://datazone.birdlife.org/species/factsheet/hook-billed-bulbul-setornis-criniger on 03/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 03/12/2023.