The Caroline Ground-dove (Alopecoenas kubaryi) is endemic to the Federated States of Micronesia, occurring on the islands of Pohnpei and Chuuk, where it has been recorded on Tol, Weno, Patta, Dublon, Fenepi and Ipis Islands (D. W. Buden in litt. 2016, Baptista et al. 2020, eBird 2020). Several individuals have also been detected on Ant Atoll (D. Kesler in litt. 2012).
The population size has probably always been low (Baker 1951, Engbring et al. 1990). On Pohnpei, the population was estimated at 841 individuals in 1983-1984, and on Chuuk it was estimated to number 294 individuals in 1983-1984 (Engbring et al. 1990). In 1994, a repeat survey on Pohnpei recorded a decrease in encounter rate in the lowlands (Buden 2000, F. Amidon in litt. 2007). In 2012, a survey was carried out at 247 stations on 19 transects across Pohnpei and only five individuals were recorded (Oleiro 2014). Also on Chuuk, a population estimate in 2001 indicated a significantly smaller population than in 1983-1984 (G. Dutson in litt. 2001).
On Pohnpei, predation by introduced species (mainly rats Rattus spp. and cats) and excessive hunting may have caused some depletion (Buden 2000). Habitat loss also constitutes a threat. Overall, there was a reduction of undisturbed upland forest on Pohnpei of over 60% from 1975-1995 (B. Raynor in litt. 1995, Buden 1996, 2000, B. Raynor in litt. 2012), with habitat change slowing between 1994 and 2002 (Oleiro et al. 2014). In the elevation zone up to 100 m on Pohnpei, the area of undisturbed habitat decreased by 16% between 1975 and 1994, but changed little between 1994 and 2002 (Oleiro 2014). The majority of the island’s forests have been, to varying degrees, converted or at least degraded to mixed forest (native species mixed with lowland secondary species), largely attributable to the cultivation of sakau (kava) Piper methysticum as a major cash-crop (B. Raynor in litt. 2012).
Caroline Ground-dove is currently listed as Vulnerable on the basis of its small population. However, the sizes of the species’s subpopulations have not previously been quantified and, depending on the size of the largest subpopulation, the species could quality as Endangered. Hence, we are undertaking a review of the species’s Red List Category.
Criterion A – On Pohnpei, the population was estimated at 841 individuals in 1983-1984 (Engbring et al. 1990). It was found to have declined in the lowlands by 1994 (Buden 2000, F. Amidon in litt. 2007) and extensive surveys in 2012 recorded only five individuals (Oleiro 2014). On Chuuk, the population was estimated to number 294 individuals in 1983-1984 and was found to have declined by 2001 (G. Dutson in litt. 2001). This information suggests that the population size may have undergone a reduction over the past three generations (18 years; see Bird et al. 2020)*, but the magnitude of this reduction could not be quantified. Unless it is possible to suspect a percentage population reduction over three generations in the past and/or future, the species cannot be assessed under Criterion A. If it is suspected that the population size has undergone a reduction of 30% or more over the past 18 years, then the species may qualify as threatened under Criterion A2. We therefore ask for recent information on the magnitude of population declines over 18 years.
Criterion B – The Extent of Occurrence (EOO) is 30,000 km2, based on the area of a minimum convex polygon around the species’s range. This does not approach the threshold for listing the species as threatened under Criterion B1. The species is therefore assessed as Least Concern under this criterion.
Based on a 4km2 grid placed over the area of mapped range (Pohnpei, Tol, Weno, Patta, Dublon, Fenepi and Ipis Islands and Ant Atoll), the Area of Occupancy (AOO) must be smaller than 732 km2. Since it is unlikely that all of the mapped range is occupied, the AOO is placed in the band 400-732 km2. The lower end of this range meets the threshold for Endangered under Criterion B2. If there is evidence that the species occurs on more islands in Chuuk, then this figure may be revised upwards. To list the species as threatened on the Red List under Criterion B2, at least two further conditions must be met.
The species is not severely fragmented, since >50% of its total AOO is not in habitat patches that are either smaller than would be required to support a viable population, or separated from other habitat patches by a large distance. According to the IUCN Red List Categories and Criteria, ‘the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present’ (IUCN 2012). The main threat to the species is considered to be habitat destruction. Current evidence suggests that habitat loss is taking place slowly and that the species is likely to have more than ten locations. Therefore, condition a is not met. Nevertheless, due to the low rates of habitat loss condition b(iii) is met. Depending on the evidence of a continuing decline in the population size, condition b(v) may additionally be met. We have no information to suggest a severe fluctuation in habitat availability or population size, and so condition c is not met.
Based on current evidence, the species could qualify as Near Threatened or Least Concern under Criterion B2. However, if there is evidence to suggest that there is a plausible threat, such as the potential introduction of an invasive species, so that Caroline Ground-dove would have ten or fewer locations, the species could qualify as Vulnerable or Endangered under Criterion B2. Conversely, if the species is likely to occur on more islands than those listed here, and the AOO is thus likely to be greater than 500 km2, then the species could qualify as Vulnerable under Criterion B2 (depending on the number of locations), but not Endangered. To fully assess Caroline Ground-dove against Criterion B, we ask for recent information on the distribution range as well as on the threats that the species is facing in order to quantify the number of locations.
Criterion C – Based on the surveys described above, the total population is suspected to number 250-999 mature individuals. The species meets the population size threshold for listing as Endangered under Criterion C. The population is also inferred to be undergoing a continuing decline. To list the species as threatened on the Red List under Criterion C further conditions must also be met.
We do not have population data from which to estimate the rate of decline, so the species cannot be assessed as threatened under Criterion C1. Caroline Ground-dove is likely to have at least two subpopulations, with the largest found on the island of Pohnpei. Based on the current mapped range, which consists of the islands of Pohnpei, Tol, Weno, Patta, Dublon, Fenepi, Ipis, and Ant Atoll, Pohnpei comprises around 85% of the total range. If it is assumed to also contain 85% of the population, we may place the subpopulation size for Pohnpei within the band 200-850 mature individuals. In 2012, a survey was carried out at 247 stations on 19 transects across Pohnpei and only five individuals were recorded (Oleiro 2014), suggesting a very small population size. If the subpopulation on Pohnpei is considered likely to have fewer than 250 mature invidividuals, the species will qualify as Endangered under Criterion C2a(i). If not, the species will qualify as Vulnerable under the same Criterion.
Less than 90% of individuals are found in any one subpopulation, meaning that the species does not meet condition a(ii).There is no evidence that the species’s population size is undergoing extreme fluctuations so the species doesn’t meet condition b.
Caroline Ground-dove may therefore qualify for listing as Vulnerable or Endangered under Criterion C2a(i), depending on whether the largest subpopulation comprises fewer than 250 mature individuals. We are asking for information on the sizes and structure of the subpopulations of Caroline Ground-dove.
Criterion D – Based on the population estimates described above, the species qualifies as Vulnerable under Criterion D1. If a plausible threat (such as typhoon on Pohnpei) could result in the loss of 25% of the total population within 3 years, the species may also qualify as Vulnerable under Criterion D2. To quantify the number of locations we seek recent information on potential threats to the species and their likely impacts on the population size.
Criterion E – To the best of our knowledge no quantitative assessment of the probability of extinction has been conducted for this species, and so it cannot be assessed against this criterion.
Based on the above assessment, the species may be listed as Vulnerable or Endangered, depending on:
- the suspected percentage population reduction over 18 years
- which islands in Chuuk the species is thought to occur on, and hence the species’s AOO
- whether there is a plausible threat such as the introduction of a further invasive species that could mean that the species has five or fewer locations
- the size of the largest subpopulation.
To assess the Red List status of Caroline Ground-dove (Alopecoenas kubaryi), we particularly request information in relation to the above four points.
Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’s Red List status. Therefore, please make sure your comments are about the proposed listing. By submitting a comment, you confirm that you agree to the Comment Policy.
*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).
An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.
Baker, R. H. 1951. The avifauna of Micronesia: its origin, evolution and distribution. University of Kansas, Lawrence.
Baptista, L.F., Trail, P.W., Horblit, H.M., Christie, D.A., Kirwan, G.M., Boesman, P. & Garcia, E.F.J. 2020. Caroline Ground-dove (Alopecoenas kubaryi). Barcelona (Accessed: 1 April 2020).
Bird, J. P.; Martin, R.; Akçakaya, H. R.; Gilroy, J.; Burfield, I. J.; Garnett, S.; Symes, A.; Taylor, J.; Šekercioğlu, Ç.; Butchart, S. H. M. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.
Buden, D.W. 2000. A comparison of 1983 and 1994 bird surveys of Pohnpei, Federated States of Micronesia. Wilson Bulletin 112: 403-410.
eBird. 2020. eBird: An online database of bird distribution and abundance [web application]. Ithaca, NY, USA Available at: http://www.ebird.org.
Engbring, J.; Ramsey, F. L.; Wildman, V. J. 1990. Micronesian forest bird surveys, the Federated States: Pohnpei, Kosrae, Chuuk, and Yap. U.S. Fish and Wildlife Service, Honolulu.
IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. Gland, Switzerland and Cambridge, UK: IUCN. Available at www.iucnredlist.org/technical-documents/categories-and-criteria
Oleiro, P. 2014. Avian population responses to anthropogenic landscape changes in Pohnpei, Federated States of Micronesia. Unpublished Masters Thesis. University of Missouri.