Species

Rota White-eye (Zosterops rotensis)

Geographic Range

Endemic to Rota, Northern Mariana Islands, where it is primarily found above elevations of 150 m.

Current Category & Criteria

Critically Endangered B1ab(i,ii,iii)+2ab(i,ii,iii)

Proposed Category & Criteria

TBD

A category proposal is not decided for this species, pending the outcome of this forum consultation. We hope to reach a recommendation by the end of this forum period.

Rationale for proposed change

This species was last assessed in 2017, hence needs re-assessment very soon to avoid exceeding the 10-year limit for IUCN Red List assessments.

The species was previously categorised as Critically Endangered under Criteria B1ab(i,ii,iii)+2ab(i,ii,iii). To be listed as threatened under Criterion B a taxon must meet the range threshold and two of three required subcriteria (see Annex 2 below).

The Area of Occupancy (AOO), calculated by overlaying a 2 x 2 km grid over the mapped range, exceeds the B2 threshold of 10km² and it therefore cannot be listed as CR under this criterion. The Extent of Occurrence (EOO) does fall below the CR threshold of 100km² under B1 however, and there is considered to be a single location (defined as a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present) due to the risk of accidentally introduced Brown Tree Snakes extirpating all known individuals, which caused the rapid extinction of the related Bridled White-eye Z. conspicillatus on the island of Guam.

The species does not undergo extreme fluctuations but may meet a second subcriterion if there is a continuing decline in the number of mature individuals or in the area, extent and/or quality of habitat. However, it is currently unclear if this is the case: after a steep decline from 1982 to the late 1990s the population recovered to 1980s levels by 2012, but there is no more recent information on population trends and the threats to this species are poorly understood. Additional information is therefore needed.

In the absence of evidence for population declines, the species also does not appear to meet thresholds for listing as threatened under Criteria A or C. The population is too large to meet the threshold for Criterion D; however, it qualifies as Vulnerable under Criterion D2 on the basis of its restricted range with a plausible future threat that could drive it to CR or EX in a very short time period.

Information regarding the population size, trend and threats is sought here and will be considered in full with a view to making a recommended category during this forum window.

Type of proposed change

n/a

Timing of genuine change

n/a

Drivers of genuine change

n/a

General request

The BirdLife Red List Team has updated the information held in SIS (IUCN Red List database) on the key parameters relevant to this species (Annex 1) and then applied the IUCN Red List Criteria and guidelines to reassess its status (Annex 2). If you have any information that may affect the value of the key parameters in Annex 1, and thus potentially affect the reassessment, please contribute them directly via the Forum or by email (redlistteam@birdlife.org) by 25 January 2026.

Specific questions

Annex 1: Species data (values of key parameters) *These terms have specific definitions as described by IUCN – please refer to the glossary and definitions page.

Population size

Estimate

Minimum

Maximum

Derivation

Number of mature individuals

5,600–21,000

5,600

21,000

Estimated* 

Justification

The most recent published population estimate was 14,384 (5,620–20,961) individuals in 2012 (Camp et al. 2015, USFWS 2025). Although surveys have continued, no updated estimate of the population size is available (USFWS 2025). In the absence of more recent data, the population is tentatively placed in the band 5,600–21,000 mature individuals, but further information is sought.

Population trend

Direction/Yes/No

Minimum %

Maximum %

Derivation

Current population trend

Unknown

.

n/a

Justification

The current population trend is unknown. The population is thought to have declined from 1982, when it was estimated at 14,963 (8,741–18,487) individuals, to the late 1990s when there were estimated to be only around 2,000 birds (Camp et al. 2015, USFWS 2025). The threats are unclear, but this decline may have been driven by habitat loss and degradation owing to agricultural development and typhoons (Fancy and Snetsinger 2001). Numbers then increased and by 2012 the population had recovered to approximately 1980s levels, with an estimate of over 14,000 birds (Camp et al. 2015, USFWS 2025). Although surveys have continued, no recent analysis has been conducted (USFWS 2025) and it is therefore unclear whether the population has stabilised or continued to increase. Further information is sought.

Generation length* (years)

2.6

Generation length from BirdLife International (2025).

3 generations/10 years (years)

10

Past 3 generations/10 years

n/a

.

.

n/a

Future 3 generations/10 years

n/a

.

.

n/a

Past + future 3 generations/10 years

n/a

.

.

n/a

Justification

n/a

Continuing decline in mature individuals

Unknown

.

n/a

Justification

n/a

Continuing decline over 3 years/1 gen

n/a

.

.

n/a

Continuing decline over 5 years/2 gens

n/a

.

.

n/a

Continuing decline over 10 years/3 gens

n/a

.

.

n/a

Justification

n/a

Subpopulation structure

Number of subpopulations

No. mature individuals in largest subpopulation

% individuals in largest subpopulation

Values

1

.

100%

Justification

Assumed to function as a single subpopulation on Rota.

Trend

n/a

Derivation:

n/a

Justification

n/a

Geographic range

Value

Continuing decline?

Derivation

Extent of Occurrence EOO* (km²)

52

No

Inferred*

Area of Occupancy AOO* (km²)

52

No

Inferred*

Justification

The EOO calculated from a minimum convex polygon around the mapped range is 40 km², however this is increased to match the AOO of 52 km² sensu IUCN guidelines. The AOO is calculated by overlaying a 2 x 2 km grid over the mapped range. The trend in both metrics is inferred to be stable given the species continues to be recorded across its mapped range (eBird 2025).

Locations*

1

Unknown

n/a

Justification

The introduction of the Brown Tree Snake caused the rapid extinction of the related Bridled White-eye Z. conspicillatus on Guam. It is plausible that the introduction of snakes to Rota could similarly affect all individuals within a short time period, and the species is therefore considered to occur at a single location.

Area/extent/quality of habitat

.

Unknown

n/a

Justification

The threats to this species are unclear, but the decline from 1982 to the late 1990s may be attributed to habitat loss and degradation owing to agricultural development and typhoons (Fancy and Snetsinger 2001). The population appears to have recovered since, and it is unknown whether there is a continuing decline in the area, extent and/or quality of habitat at present. Further information is sought.

Severe fragmentation and extreme fluctuations

Yes/No

Parameter

if yes

Justification

Severely fragmented*

No

.

n/a

Extreme fluctuations*

No

.

n/a

Restricted AOO/number of locations with

a plausible future threat that could drive

the taxon to CR or EX in a very short time

Yes

.

The species is restricted to the island of Rota where the spread of Brown Tree Snakes would likely result in its rapid extirpation, as occurred with the related Bridled White-eye Z. conspicillatus on Guam.

Annex 2: Application of IUCN Red List Criteria. *These terms have specific definitions as described by IUCN – please refer to the glossary and definitions page.

Categories and Criteria thresholds

Critically Endangered

Endangered

Vulnerable

Met or approached by species?

Threshold level reached

Criterion A: Rate of population decline over 3 generations/10 years (whichever is longer)

A1

≥ 90%

≥ 70%

≥ 50%

No

.

A2

≥ 80%

≥ 50%

≥ 30%

No

.

A3

≥ 80%

≥ 50%

≥ 30%

No

.

A4

≥ 80%

≥ 50%

≥ 30%

No

.

Criterion B: Geographic range

B1: Extent of Occurrence EOO* (km²)

< 100

< 5,000

< 20,000

Met

CR

B2: Area of Occupancy AOO* (km²)

< 10

< 500

< 2000

Met

EN

And at least two of (a), (b) and (c):

(a): Severely fragmented*/Number of locations*

=1

≤ 5

≤ 10

Met

CR

(b): Continuing decline observed/estimated/inferred/projected in

(i) EOO, (ii) AOO, (iii) Habitat area/extent/quality,

(iv) Locations/subpopulations, (v) mature

individuals

Unknown

.

(c): Extreme fluctuations* in

(i) EOO, (ii) AOO, (iii) Locations/subpopulations,

(iv) mature individuals

.

No

.

Criterion C: Small population size and decline (population size must be ESTIMATED – it cannot be inferred or suspected [see IUCN Standards and Petitions Committee 2024])

Number of mature individuals

< 250

< 2,500

< 10,000

Met

VU

And at least one of C1 or C2:

C1: An observed/estimated/projected continuing decline of at least:

25% in 3

years or 1

generation

20% in 5

years or 2

generations

10% in 10

years or 3

generations

Unknown

.

C2: An observed, estimated, projected or inferred continuing decline

Unknown

.

Plus at least 1 of 3: 

.

a(i): Mature individuals per subpopulation

≤ 50

≤ 250

≤ 1,000

No

.

a(ii): % mature individuals in largest subpopulation

90-100%

95-100%

100%

Met

.

b: Extreme fluctuations* in number of mature individuals

.

No

Criterion D: Very small or restricted population (population size must be ESTIMATED – it cannot be inferred or suspected [see IUCN Standards and Petitions Committee 2024])

Number of mature individuals

< 50

< 250

D1.   

< 1,000

.

No

.

Restricted AOO/number of locations with a plausible future threat that could drive the taxon to CR or EX in a very short time

–

–

D2. Typically: AOO < 20 km² or ≤ 5 locations

Met

.

Criterion E: Quantitative Analysis

Indicated probability of extinction in the wild (in 100 years max)

≥ 50% in longer

of 10 years/3 generations

≥20% in longer

of 20 years/5 generations

≥ 10% in 100 years

n/a

.

Proposed Red List Category

.

The Red List status of this species is considered uncertain (see above).

Species Range Map

.

References

BirdLife International. 2025. Generation lengths of the world’s birds. Version 3.1 (August 2025). Available at: https://datazone.birdlife.org.

Camp, R.J., Brinck, K.W., Gorresen, P.M., Amidon, F.A., Radley, P.M., Berkowitz, S.P. and Banko, P.C. 2015. Current land bird distribution and trends in population abundance between 1982 and 2012 on Rota, Mariana Islands. Journal of Fish and Wildlife Management 6: 511-540.

eBird. 2025. eBird: An online database of bird distribution and abundance [web application]. Ithaca, New York. eBird, Cornell Lab of Ornithology. Available at: http://www.ebird.org.

Fancy, S.G. and Snetsinger, T.J. 2001. What caused the decline of the Bridled White-eye on Rota, Mariana Islands? Studies in Avian Biology 22: 274-280.

IUCN Standards and Petitions Committee. 2024. Guidelines for Using the IUCN Red List Categories and Criteria. Version 16. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

U.S. Fish and Wildlife Service (USFWS). 2025. Rota white-eye (Zosterops rotensis) 5-year review summary and evaluation. U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office, Honolulu, Hawaii.