• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Taxonomic note

Laniellus langbianis (del Hoyo and Collar 2016) was previously listed as Crocias langbianis.

Taxonomic source(s)
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A., Fishpool, L.D.C., Boesman, P. and Kirwan, G.M. 2016. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 2: Passerines. Lynx Edicions and BirdLife International, Barcelona, Spain and Cambridge, UK.

Red List criteria met

Critically Endangered	Endangered	Vulnerable
-	-	-

Red List history

Year	Category	Criteria
2024	Near Threatened	A2c+3c+4c
2016	Endangered	B1ab(i,ii,iii,iv,v); C2a(ii)
2012	Endangered	B1ab(i,ii,iii,iv,v)
2008	Endangered	B1a+b(i,ii,iii,iv,v)
2004	Endangered
2000	Endangered
1996	Critically Endangered
1994	Critically Endangered
1988	Threatened

Migratory status	not a migrant	Forest dependency	high
Land-mass type	continent	Average mass	-

	Estimate	Data quality
Extent of Occurrence (breeding/resident)	47,600 km2	medium
Number of locations	11-100	-
Severely fragmented?	no	-

	Estimate	Data quality	Derivation	Year of estimate
Population size	unknown	-	-	-
Population trend	decreasing	poor	suspected	2016-2027
Rate of change over the past 10 years/3 generations (longer of the two periods)	5-29,15-29%	-	-	-
Rate of change over the future 10 years/3 generations (longer of the two periods)	5-29,15-29%	-	-	-
Rate of change over the past & future 10 years/3 generations (longer of the two periods)	5-29,15-29%	-	-	-
Generation length	3.79 years	-	-	-
Number of subpopulations	2-50	-	-	-
Percentage of mature individuals in largest subpopulation	1-89%	-	-	-

Population justification: The population size of this species has never been estimated. On the Dalat Plateau, Viet Nam, it is evidently highly localised (Eames et al. 1995, Mahood and Eames 2012, eBird 2023) with no obvious correlating habitat variables between confirmed sites to enable even a crude estimation of what percentage of its mapped range might be occupied. In the Mang Den region (Kon Tum province, Viet Nam) it appears to be more (at least locally) abundant (Wheatley 2015); while here it is confirmed from only a relatively small area, the total area of suitable habitat is considerably larger (and very poorly explored). The species' recent discovery in Dong Ampham, Lao PDR (Berryman 2023) [approximately 100 km north-west], in habitat broadly identical to that the species is found in Mang Den (A. Berryman pers. obs) supports suggestion that the species is probably more widespread in this section of the Annamites, although may remain very localised.
Given the great uncertainty over this species' true distribution (or, more accurately, great uncertainty about its habitat preferences and tolerances within it), the population size is here considered unknown. However, given the area of forest within the mapped range covers c.8,000km² (and this may prove an underestimate), even if only a very small proportion of this is occupied (as seems probable), the population size is unlikely to be very small given its local abundance (e.g., approximately 40 birds encountered in a relatively small area of the Mang Den forests: Wheatley 2015).

Trend justification: Suspected to be declining in response to habitat loss and degradation. There is no direct evidence that the species is trapped for the cagebird trade (unlike its sole congener: Nijman et al. 2021).
Given uncertainties over this species' range, and abundance throughout it, determining plausible rates of decline is challenging. This difficulty is made only more acute by a lack of understanding of its habitat tolerances. At most occupied sites, it inhabits native forest that is either primary or only lightly degraded; however, at others (e.g. Ta Nung Valley, Da Lat), it persists in very degraded forests, while being inexplicably absent from surrounding, less modified, areas. Nonetheless, within its probable range, forest cover loss has occurred moderately rapidly in recent years, equivalent to rates of 8-27% over the past three generations (11 years: 2011-2022) with uncertainty principally driven by the difficulties in determining its range (Global Forest Watch 2023, based on data from Hansen et al. [2013] and methods disclosed therein). Translating this into plausible bounds of population decline introduces even greater uncertainty with respect to habitat modification tolerances. Possible rates of population decline are therefore set broadly, as between 5 and 29% over the past three generations, with a precautionary best estimate at the upper end of this (15-29%). Future rates of decline are set the same in the absence of any indication that forest cover loss has recently slowed.

Country/Territory	Presence	Origin	Resident	Breeding visitor	Non-breeding visitor	Passage migrant
Laos	extant	native	yes
Vietnam	extant	native	yes

Country/Territory	IBA Name
Vietnam	Chu Yang Sin
Vietnam	Tuyen Lam

Habitat (level 1)	Habitat (level 2)	Importance	Occurrence
Artificial/Terrestrial	Subtropical/Tropical Heavily Degraded Former Forest	marginal	resident
Forest	Subtropical/Tropical Moist Montane	major	resident
Altitude	900 - 1700 m	Occasional altitudinal limits

Threat (level 1)	Threat (level 2)	Impact and Stresses
Agriculture & aquaculture	Annual & perennial non-timber crops - Agro-industry farming	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Ecosystem degradation, Ecosystem conversion
Agriculture & aquaculture	Annual & perennial non-timber crops - Shifting agriculture	Timing		Scope		Severity		Impact
		Ongoing		Whole (>90%)		Slow, Significant Declines		Medium Impact: 7
		Stresses Ecosystem degradation, Ecosystem conversion
Biological resource use	Logging & wood harvesting - Unintentional effects: (large scale) [harvest]	Timing		Scope		Severity		Impact
		Ongoing		Whole (>90%)		Slow, Significant Declines		Medium Impact: 7
		Stresses Ecosystem degradation, Ecosystem conversion
Biological resource use	Logging & wood harvesting - Unintentional effects: (subsistence/small scale) [harvest]	Timing		Scope		Severity		Impact
		Ongoing		Whole (>90%)		Slow, Significant Declines		Medium Impact: 7
		Stresses Ecosystem degradation, Ecosystem conversion
Energy production & mining	Mining & quarrying	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Negligible declines		Low Impact: 4
		Stresses Ecosystem degradation, Ecosystem conversion

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Recommended citation
BirdLife International (2024) Species factsheet: Grey-crowned Crocias Laniellus langbianis. Downloaded from https://datazone.birdlife.org/species/factsheet/grey-crowned-crocias-laniellus-langbianis 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.