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

Taxonomic note

Gerygone magnirostris and G. hypoxantha (del Hoyo and Collar 2016) were previously lumped as G. magnirostris following Christidis & Boles (2008) and Sibley & Monroe (1990, 1993).

 

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.
Morony, J. J.; Bock, W. J.; Farrand, J. 1975. Reference list of the birds of the world. Department of Ornithology, American Museum of Natural History, New York.

Red List criteria met

Critically Endangered	Endangered	Vulnerable
-	-	-

Red List history

Year	Category	Criteria
2023	Near Threatened	B1b(iii)
2016	Vulnerable	C2a(ii)
2012	Not Recognised
2008	Not Recognised
2007	Not Recognised
2004	Endangered
2000	Endangered
1994	Endangered
1988	Threatened

Migratory status	not a migrant	Forest dependency	medium
Land-mass type		Average mass	7 g

	Estimate	Data quality
Extent of Occurrence (breeding/resident)	3,600 km2
Severely fragmented?	no	-

	Estimate	Data quality	Derivation	Year of estimate
Population size	15000-45000 mature individuals	poor	suspected	2022
Population trend	decreasing	-	suspected	2017-2027
Rate of change over the past 10 years/3 generations (longer of the two periods)	1-9%	-	-	-
Rate of change over the future 10 years/3 generations (longer of the two periods)	1-9%	-	-	-
Rate of change over the past & future 10 years/3 generations (longer of the two periods)	1-9%	-	-	-
Generation length	2.92 years	-	-	-
Number of subpopulations	1	-	-	-
Percentage of mature individuals in largest subpopulation	100%	-	-	-

Population justification: The population size of this species has not previously been directly quantified. Other species of Gerygone occur at quite high densities (20-400 birds/km²; e.g. Fogden 1976, Bell 1982), although qualitatively G. hypoxantha is considered rare (Pratt and Beehler 2015, Beehler and Pratt 2016), while the limited eBird (2022) data available support that it may occur at lower densities than congeners. Using the global landcover 2 estimate of forest cover for the island (closed to open broadleaved evergreen or semi-deciduous forest) and excluding fragments smaller than 1 km² results in an area classified as forest habitat of 1,572 km². Consequently, assuming (somewhat precautionarily) a combined occupancy/density of 10-30 mature individuals/km², the population is suspected of numbering 15,000-45,000 mature individuals, although there remains high uncertainty with this.

Trend justification: No direct assessment of rate of population change has been made for the species. It is considered to be forest dependent and there has been a slow rate of forest cover loss, up to 4% in the ten years to 2022 (data from Global Forest Watch 2022, using Hansen et al. [2013] data and methods disclosed therein) and this is suspected to be causing broadly equivalent reductions in population size of this species.

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

Country/Territory	IBA Name

Habitat (level 1)	Habitat (level 2)	Importance	Occurrence
Forest	Subtropical/Tropical Dry	suitable	resident
Forest	Subtropical/Tropical Mangrove Vegetation Above High Tide Level	major	resident
Forest	Subtropical/Tropical Moist Lowland	suitable	resident
Shrubland	Subtropical/Tropical Moist	suitable	resident
Altitude	0 - 600 m	Occasional altitudinal limits

Threat (level 1)	Threat (level 2)	Impact and Stresses
Agriculture & aquaculture	Annual & perennial non-timber crops - Shifting agriculture	Timing		Scope		Severity		Impact
		Ongoing						Low Impact: 3
		Stresses Ecosystem degradation, Ecosystem conversion
Biological resource use	Logging & wood harvesting - Unintentional effects: (large scale) [harvest]	Timing		Scope		Severity		Impact
		Ongoing						Low Impact: 3
		Stresses Ecosystem degradation, Ecosystem conversion

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Recommended citation
BirdLife International (2024) Species factsheet: Biak Gerygone Gerygone hypoxantha. Downloaded from https://datazone.birdlife.org/species/factsheet/biak-gerygone-gerygone-hypoxantha on 24/11/2024.
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 24/11/2024.