Species

Mariana Crow (Corvus kubaryi)

Geographic Range

Endemic to Rota, Northern Mariana Islands. Formerly occurred on Guam, where it was extirpated in the late 1990s following the introduction of the Brown Tree Snake.

Current Category & Criteria

Critically Endangered A2bcde+3bcde+4bcde; C2a(ii)

Proposed Category & Criteria

Endangered D

Rationale for proposed change

This species was previously assessed as Critically Endangered under Criteria A2bcde+3bcde+4bcde on the basis of extremely rapid population declines exceeding the threshold of 80% over a period of three generations (c. 21 years). However, this trend has since slowed and the population, though severely depleted relative to historical levels, is now increasing. As such, the rate of reduction over the most recent three-generation period (2005-2026) no longer meets this threshold.

Given the population trend is now increasing, the species also no longer qualifies as Critically Endangered under C2a(ii) which requires there to be an observed, estimated, projected or inferred continuing decline in mature individuals.

The population size remains very small, and it is therefore proposed to be reassessed as Endangered under Criterion D.

Type of proposed change

Genuine change

Timing of genuine change

A captive rear–and-release program was initiated in 2015, and the population has been increasing since. The timing of genuine change is therefore placed in the period 2012-2016 for the Red List Index.

Drivers of genuine change

See above.

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 17 May 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

146

.

Estimated*

Justification

The population was most recently estimated at 146 breeding adults in 2025 (USFWS 2025).

Population trend

Direction/Yes/No

Minimum %

Maximum %

Derivation

Current population trend

Increasing

.

Estimated*

Justification

In 1984 there were estimated to be 150-200 individuals on Guam and approximately 1,300 individuals on Rota. The population on Guam was extirpated in the late 1990s following the introduction of the Brown Tree Snake, and the population on Rota declined sharply down 92 breeding adults by 2014, likely a result of high mortality in first-year birds driven by feral cat predation (Camp et al. 2015, USFWS 2025).

A captive rear–and-release program was initiated in 2015, and the population has been increasing since: there were estimated to be 102 breeding adults in 2020 and 146 in 2025 (USFWS 2025).

Generation length* (years)

6.9

Generation length from BirdLife International (2025).

3 generations/10 years (years)

20.7

Past 3 generations/10 years

Reduction

15

Estimated*

Future 3 generations/10 years

n/a

n/a

n/a

Past + future 3 generations/10 years

n/a

n/a

n/a

Justification

In 2005 the population was estimated at 170 breeding adults. It then decreased to a low of 92 in 2014, before increasing to 146 in 2025 following the initiation of a captive rear-and-release programme in 2015. The overall population reduction over the past three generations (2005-2026) is therefore estimated at approximately 15%.

Continuing decline in mature individuals

No

.

Estimated*

Justification

A captive rear–and-release program was initiated in 2015, and the population has been increasing since (USFWS 2025).

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

146

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)

120

No

Inferred*

Justification

The EOO, calculated from a minimum convex polygon around the mapped range, is 108 km², however this is increased to match the AOO of 120 km² sensu IUCN guidelines. The trend is inferred to be stable given the species continues to be recorded across its mapped range (eBird 2026).

Area of Occupancy AOO* (km²)

120

No

Inferred*

Justification

The AOO is calculated by overlaying a 2 x 2 km grid over the mapped range. The trend is inferred to be stable given the species continues to be recorded across its mapped range (eBird 2026).

Locations*

1

n/a

n/a

Justification

The introduction of the Brown Tree Snake caused the rapid extinction of this species 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 species appears to utilise a range of habitats and there is currently no evidence for a continuing decline in the area, extent and/or quality of habitat. However, further information on this 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 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

EN

B2: Area of Occupancy AOO* (km²)

< 10

< 500

< 2,000

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

No

.

(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

CR

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

No

.

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

No

.

Plus at least 1 of 3: 

.

a(i): Mature individuals per subpopulation

≤ 50

≤ 250

≤ 1,000

Met

EN

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

.

Met

EN

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

.

This species is proposed to be assessed as Endangered.

.

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. 2026. 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.

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. Aga or Mariana crow (Corvus kubaryi) 5-year review summary and evaluation. Honolulu, Hawaii. U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office.