Data Zone
Justification of Red List category
Cyornis caerulatus is listed as Vulnerable under A2cd+3cd+4cd. The extensive clearing and degradation of lowland forests on Borneo and Sumatra has resulted in declines in suitable habitat of c. 20% over the past ten years. However, the extreme rarity of the species suggests rapid declines from threats that are not completely understood. It is suspected that the trade of the species has had, and will continue to have, a profound impact on the population. These impacts are inferred from the popularity of the genus in trade, and the rapid declines of the closely related C. banyumas. Consequentially, declines in the range of 20-40% are suspected.
Population justification
The population size of Cyornis caerulatus is unknown. The species is considered uncommon to locally common on Borneo but appears very rare on Sumatra (BirdLife International 2001, Hua et al. 2011, Clement 2020). Most recent records of the species are clustered in the north-eastern corner of Sabah (Hua et al. 2011, eBird 2024). The species is patchily recorded throughout the rest of Borneo, which may in part reflect survey effort across the island (Hua et al. 2011), with recent records outside of Sabah from Gunung Mulu National Park and Kubah National Park in north and south-eastern Sarawak, respectively (eBird 2024). Regardless of survey effort, the species appears to occur at low densities even in undisturbed suitable habitat (Slik and van Balen 2005, Ansell et al. 2010, Hua et al. 2011), but has been recorded as locally common in central Kalimantan (Fischer et al. 2016), suggesting small pockets of high density populations may occur. On Sumatra, the species appears to have always been rare (van Marle and Voous 1988, BirdLife International 2001, Hua et al. 2011). The only Sumatran records this century are one observation from Kerinci Seblat National Park, Bengkulu (Hutchinson 2006), four individuals from Solok Selatan in west Sumatra (Kemp 2008 in Hua et al. 2011), and six individuals from Harapan Rainforest Restoration Site (Hua et al. 2011). Overall, this reflects a likely very small, localised, and patchily distributed population. However, it is not possible to estimate the total population size from current information.
Trend justification
C. caerulatus occupies lowland primary forest (Clement 2020), a habitat type that has been cleared at alarming rates both historically and contemporarily (BirdLife International 2001, FWI/GFW 2002, Sodhi et al. 2004). Forest loss within the range of the species over the past ten years has been c.19-21% (Global Forest Watch 2024, based on data from Hansen et al. [2013] and methods therein). However, forest loss data alone likely underestimate declines as they do not account for habitat degradation, which is likely to cause declines in this forest-dependent species and has been substantial in scale and intensity across the species' range (Global Forest Watch 2024, based on data from Grantham et al. [2020]), particularly as the species has been shown to occur in reduced numbers and abundance in selectively logged areas (Lambert 1992, Ansell et al. 2010).
On Sumatra, the species has only been recorded on three occasions from three separate areas this century (Hutchinson 2006, Kemp 2008 in Hua et al. 2011, Hua et al. 2011). There is a need for much improved survey coverage (Hua et al. 2011) and the species seems to always occur at low densities (e.g., see historical records in BirdLife International [2001] and Hua et al. [2011]), including in intact suitable habitat (Slik and van Balen 2005, Ansell et al. 2010). However, this rarity is reasonably partly caused by the high levels of deforestation and habitat degradation on Sumatra (Grantham et al. 2020). Without improved survey effort, it is difficult to infer local extinctions, but it seems likely that the species has disappeared from Way Kambas National Park, with one pair recorded in 1989 (Lewis et al. 1989 in BirdLife International 2001) and no records since this time despite reasonable survey coverage (eBird 2024). Regardless, these disjunct records of a small number of individuals highlight the very high risk of local extinctions in these areas, and on Sumatra in general.
There is little information specific to this species, but it is very likely that it is also impacted by the cage bird trade. Cyornis flycatchers are highly popular in the cage bird trade (BirdLife International 2001, Eaton et al. 2021), and the lack of reports of C. caerulatus in trade is likely due to misidentification rather than low demand. The species is clearly traded at higher numbers than available reports suggest, with one seizure from east Java in 2018 reporting 154 individuals shipped from southern Kalimantan (TRAFFIC 2024). The increasing rarity of the highly in demand C. banyumas (Chng et al. 2015, Kirwan et al. 2021, BirdLife International 2024) may also suggest that C. caerulatus will be increasingly targeted to cover this gap in the market. Symes et al. (2018) also predicted a reduction of c. 34% over the past ten years from trapping by assigning probability curves according to expert opinion on trade desirability in conjunction with accessibility (based on a distance to forest edge from remote sensed forest data). This analysis had no term to account for reproduction, and was largely speculative, but provides evidence that the species is certainly targeted for trade locally and occurs in areas accessible to poachers.
The impacts of trade and habitat loss/degradation on the population of C. caerulatus are suspected to be much higher than current available data suggests. Furthermore, Maxent habitat modelling using Special Report on Emissions Scenarios A1B and B1 predict a further c. 6-26% decline in suitable habitat on Borneo by 2050 caused by climate change (Singh et al. 2021). The cumulative impacts of these pervasive threats suggest ongoing declines in the population are likely in the range of 20-40% over ten years.
Cyornis caerulatus is patchily distributed through Sumatra and Kalimantan, Indonesia, Sabah and Sarawak, Malaysia, and Brunei (BirdLife International 2001).
C. caerulatus occurs in lowland primary forest up to 500 m, generally in the interior or the edge of clearing in the mid-strata (Pearson 1975, BirdLife International 2001, Clement 2020). The species appears to be replaced in riverine habitats by the more abundant C. turcosus (Clement 2020).
C. caerulatus occupies lowland primary forest (Clement 2020), a habitat type that has been extensively cleared in the Sundaic region for decades (BirdLife International 2001, Haryoko et al. 2020). The vast majority of habitat loss has been driven by the widespread conversion of Borneo's lowland forests into palm-oil and rubber plantations (Descal et al. 2021, Wang et al. 2023). Even protected areas in this region are impacted by both small- and large- scale logging impacts (BirdLife International 2001). Particularly, the species appears to be sensitive to disturbance such as selective logging. For example, Cyornis flycatchers (including C. caerulatus) were completely absent from a selectively logged plot in lowland forest of Ulu Segama Forest Reserve, Sabah, as opposed to a mist-net capture rate for C. caerulatus of 2.77 birds/km of net/10 hours in primary forest (Lambert 1992). Similarly, the species was found in higher overall abundance and with a higher capture rate in undisturbed forest in the Danum Valley Conservation Reserve in Sabah, compared with both nearby naturally regenerating and rehabilitated regenerating forests that were logged in 1988-89 (Ansell et al. 2010, Hua et al. 2011). However, the species appeared to persist in similar numbers in unlogged forest compared with once- and twice-logged forest in Yayasan Sabah logging concession in Sabah (Supplemental Material in Edwards et al. 2010), but its presence may be influenced by landscape factors such as the proximity to undisturbed forest patches (Lambert 1992). Regardless, declines are very likely considering the scale and intensity of habitat degradation within the species’ range (Global Forest Watch 2024, based on data from Grantham et al. [2020]).
Fire may also pose a threat to the species, by similarly degrading habitat quality. The species was recorded an average of 0.06 times per plot in an undisturbed forest patch in east Kalimantan but was not recorded in adjacent once- or twice-burned forest (Slik and van Balen 2006). Logging is expected to increases the likelihood of fires in Sumatra and Borneo, and half of lowland regions on Kalimantan are reportedly at high risk repeated fires due to high-intensity deforestation (BirdLife International 2001).
The future loss of suitable habitat may also occur as a result of climate change, with Maxent habitat modelling using Special Report on Emissions Scenarios A1B and B1 predicting a c. 6-26% decline in suitable habitat on Borneo by 2050 (Singh et al. 2021), further exacerbating the impacts of habitat clearing and degradation and reducing suitable habitat in protected areas.
C. caerulatus is also suspected to be highly threatened from the cage bird trade, despite the paucity of information specific to this species. This threat is inferred from the popularity of Cyornis flycatchers in trade in general (BirdLife International 2001), and the fact that it may often be misreported/misidentified as the highly traded C. banyumas and/or that demand for C. caerulatus may increase with the rising rarity of C. banyumas (Jepson et al. 2011, Eaton et al. 2015, BirdLife International 2024). A 2018 seizure of 154 C. caerulatus individuals (TRAFFIC 2024) suggests that it is certainly traded in higher numbers than current information may suggest.
Conservation Actions Underway
It has been recorded in various protected areas throughout its range, including Sepilok Forest Reserve (Sabah), Gunung Mulu National Park (Sarawak), Kutai National Park (Kalimantan), Kerinci-Seblat and Way Kambas National Parks (Sumatra; Clement 2020), and the Harapan Rainforest ecosystem restoration site (Hua et al. 2011).
14 cm. Medium-sized blue (male) or brown-and-blue (female) forest flycatcher with broad-based bill. Male nominate race has deep blue face and upperparts (including upperwing and tail), except for blackish-blue lores to eye, cheek, chin and sides of throat, and brighter blue forehead, lower back and rump; centre of throat buff or buffish-orange, becoming deeper orange on breast, and fading on belly to whitish undertail-coverts; iris dark; bill black; legs dark grey. Distinguished from very similar C. rufigastra by slightly smaller size, paler or brighter blue forehead and lower back and rump (not uniform in colour); from C. turcosus by slightly larger size, orange-buff (not blue) throat, pale of forehead not extending over eyes, and duller blue on lesser coverts. Female has head to mantle, back and wings brown (mantle and lesser coverts sometimes bluish), lower back, rump and tail dull blue, pale eyering and underparts as male. Juvenile undescribed. Race rufifrons male is deeper orange-rufous on underparts than nominate, and female usually has bluer scapulars and wing-coverts; albiventer is whiter on lower belly to undertail-coverts. Sounds: Song two or three phrases of thin, metallic, rising and falling notes, “si-si-tiuuuw”; resembles song of Cyornis umbratilis, but without introductory “ziit”.
Text account compilers
Richardson, L.
Contributors
Brickle, N., Poulsen, M., Benstead, P., Gilroy, J. & Derhé, M.
Recommended citation
BirdLife International (2024) Species factsheet: Large-billed Blue Flycatcher Cyornis caerulatus. Downloaded from
https://datazone.birdlife.org/species/factsheet/large-billed-blue-flycatcher-cyornis-caerulatus on 23/11/2024.
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 23/11/2024.