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

Taxonomic note

Acrocephalus luscinius, A. hiwae, A. yamashinae, A. astrolabii and A. nijoi (del Hoyo and Collar 2016) were previously lumped as A. luscinius following 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.

Red List criteria met

Critically Endangered	Endangered	Vulnerable
-	B1ab(iii,v)+2ab(iii,v); C2a(ii)	B1ab(iii,v)+2ab(iii,v); C2a(ii); D1+2

Red List history

Year	Category	Criteria
2024	Endangered	B1ab(iii,v)+2ab(iii,v); C2a(ii)
2016	Critically Endangered	A3bce+4bce
2012	Not Recognised
2008	Not Recognised
2004	Not Recognised
2000	Not Recognised
1994	Not Recognised
1988	Not Recognised

Migratory status	not a migrant	Forest dependency	low
Land-mass type		Average mass	28 g

	Estimate	Data quality
Extent of Occurrence (breeding/resident)	2,550 km2	medium
Area of Occupancy (breeding/resident)	200 km2
Number of locations	2	-
Severely fragmented?	no	-

	Estimate	Data quality	Derivation	Year of estimate
Population size	600-5700, 2200-3300 mature individuals	good	estimated	2010
Population trend	decreasing	medium	inferred	2009-2026
Generation length	2.59 years	-	-	-
Number of subpopulations	2	-	-	-
Percentage of mature individuals in largest subpopulation	1-89%	-	-	-

Population justification: In 2007 the population on Saipan was estimated at 2,742 birds (95% CI = 1,686 - 3,956) (Camp et al. 2009). The population on Alamagan was estimated to number 946 individuals (95% CI = 428-1,762) in 2010, comprising c.25% of the global population (Marshall et al. 2011, 2021). Combining these generates a global population estimate of 3,688 (95% CI = 1,019-6,356) birds (Marshall et al. 2021). Given that only a proportion likely refer to mature individuals and that the population has probably declined further following declines recorded between 1982 and 2007, the population is tentatively placed here in the band 600-5,700 mature individuals, with a best estimate of 2,200-3,300.

Trend justification: Abundance on Saipan declined from 6,658 birds (5,331-8,054) in 1982 down to 4,639 (3,669-5,689) birds in 1997, and has continued to decline to 2,742 birds (1,686-3,956) in 2007 (Camp et al. 2009). This suggests an accelerating decline equating to 40% between 1997 and 2007. Declines are thought to be driven by habitat loss in line with extensive economic development of the island, degradation due to the spread of non-native plants as well as predation from introduced rats and cats (Camp et al. 2009). The human population on Saipan is no longer rapidly expanding however and the conversion of forest to anthropogenic-dominated habitats is likely to have slowed. Population estimates for the Alamagan population show little variation but declined slightly from 1,125 (504-1,539) birds in 2000 to 946 (428-1,762) in 2010 and may decline significantly in the future as native forest continues to be overgrazed by feral ungulates (Marshall et al. 2021). However, it may be the case that the species has co-existed with ungulates on the island for several centuries (Commonwealth of the Northern Mariana Islands [CNMI] in litt. 2024). There are no more recent data on population trends, but habitat loss and degradation, as well as predation by introduced mammals, continue to be considered primary threats to the species (USFWS 2020). Declines are therefore inferred to be ongoing, though the rate has not been quantified.

Country/Territory	Presence	Origin	Resident	Breeding visitor	Non-breeding visitor	Passage migrant
Northern Mariana Islands (to USA)	extant	native	yes

Country/Territory	IBA Name
Northern Mariana Islands (to USA)	Alamagan Island
Northern Mariana Islands (to USA)	Northern Saipan
Northern Mariana Islands (to USA)	Topachau-Susupe-Kagman

Habitat (level 1)	Habitat (level 2)	Importance	Occurrence
Forest	Subtropical/Tropical Mangrove Vegetation Above High Tide Level	suitable	resident
Forest	Subtropical/Tropical Moist Lowland	suitable	resident
Shrubland	Subtropical/Tropical Moist	suitable	resident
Wetlands (inland)	Bogs, Marshes, Swamps, Fens, Peatlands	suitable	resident
Wetlands (inland)	Permanent Freshwater Lakes (over 8ha)	suitable	resident
Wetlands (inland)	Permanent Freshwater Marshes/Pools (under 8ha)	suitable	resident
Altitude	0 - 400 m	Occasional altitudinal limits

Threat (level 1)	Threat (level 2)	Impact and Stresses
Agriculture & aquaculture	Annual & perennial non-timber crops - Small-holder farming	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Ecosystem degradation, Ecosystem conversion
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Boiga irregularis	Timing		Scope		Severity		Impact
		Future		Majority (50-90%)		Very Rapid Declines		Medium Impact: 6
		Stresses Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Bos taurus	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Indirect ecosystem effects, Ecosystem degradation
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Capra hircus	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Indirect ecosystem effects, Ecosystem degradation
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Coccinia grandis	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Ecosystem degradation
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Felis catus	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Named species	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Reduced reproductive success, Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Sus scrofa	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Indirect ecosystem effects, Ecosystem degradation
Invasive and other problematic species, genes & diseases	Problematic native species/diseases - Varanus indicus	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Negligible declines		Low Impact: 4
		Stresses Species mortality
Residential & commercial development	Housing & urban areas	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Ecosystem degradation, Ecosystem conversion
Residential & commercial development	Tourism & recreation areas	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Ecosystem degradation, Ecosystem conversion

Purpose	Scale
Pets/display animals, horticulture	international

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Recommended citation
BirdLife International (2024) Species factsheet: Saipan Reed-warbler Acrocephalus hiwae. Downloaded from https://datazone.birdlife.org/species/factsheet/saipan-reed-warbler-acrocephalus-hiwae on 26/12/2024.
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 26/12/2024.