Archived 2020 topic: Caroline Ground-dove (Alopecoenas kubaryi): request for information

BirdLife species factsheet for Caroline Ground-dove

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.

References

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.

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5 Responses to Archived 2020 topic: Caroline Ground-dove (Alopecoenas kubaryi): request for information

  1. Red List Team (BirdLife International) says:

    The following comment was received from Chris Collins via email on 22nd June:

    Caroline Ground Dove

    I have been to Chuuk, Micronesia on multiple occasions over the last 16 years as part of an extended ship based birding tour I am involved with in the West Pacific. The info on the BL website asked for which islands the species is known to occur on in Chuuk. We have only visited Weno and Tol and the species is definitely present on both and we have seen it there in recent years, eg at least eleven individuals were seen on Weno in 2019. Last year, we followed the coastal road around approximately five miles of the coast on the northern side of Weno and observed six individuals in degraded habitat over the course of a couple of hours or so. Previously I had always taken the groups to a spot known as ‘Japanese Gun’ where this species is reasonably regular (we typically see up to half a dozen or so individuals there over the course of a couple of hours) so it was good to see it elsewhere and in unexpectedly good numbers. There is now very little good quality native habitat on Weno whereas on Tol, the higher parts of the island are still extensively covered in native forest. Our experience in 2019 confirmed, however, that the species is able to survive in scrub.

    With regards to threats, there is massive loss of native habitat in this region (eg essentially no pristine habitat left on Weno) and the children especially do kill birds with catapults etc so personally I would certainly regard this species as remaining threatened.

    I have not visited any other islands (apart from Tol) but given our recent experience of finding it in such degraded habitat on Weno, I would anticipate it is highly likely to occur on some of the other islands.

    Looking at the species factsheet ie https://globally-threatened-bird-forums.birdlife.org/2020/06/caroline-ground-dove-alopecoenas-kubaryi-request-for-information/ I would like to suggest that the comment that this species has an “extent of occurrence” of 30,000kms is verging on nonsense as most of this is ocean !!!!

  2. Robert Davis says:

    This review is well considered and highlights the major knowledge gaps that are required for accurate assessment, namely accurate distributional information and trend data on populations. Although I cannot provide those, except to say that I have not seen it on Pohnpei. It would seem apparent that it is extremely rare on Pohnpei as the work by Kessler and Oleiro was comprehensive and would likely have detected this species well. Their work was also able to compare to past surveys and has therefore shown a clear decline. There are also few e-bird records from Pohnpei. It would appear that birdwatchers find the specie more regularly on Chuuk and e-bird bears testament to this. So the impression is that the species has declined to the point of becoming vanishingly rare on Pohnpei but may be stable or declining at a lesser rate on Chuuk.

    The threats have not been addressed and the impact of cats especially is well known to be devastating for ground dwelling birds in the Pacific. Given the lack of threat mitigation and increasing loss of habitat on Pohnpei and Chuuk, it would be reasonable to argue that the threats may be continuing to negatively affect populations. The conceivable introduction of the brown tree snake is a major threat that cause the extirpation of the Pohnpei population and has been previously considered in the assessments for Pohnpei Kingfisher. The loss of the Pohnpei population is quite possible due to ongoing habitat loss for Sakau, farms and the lack of mitigation of cats and rats.

    The species easily qualifies for Vulnerable but Endangered would seem appropriate based on the documented decline on Pohnpei, the lack of recent sightings there and the ongoing threats from invasive species as well as the potential threat form brown tree snake introductions.

  3. Red List Team (BirdLife International) says:

    Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested by so many people in commenting. The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.

    Thank you once again,
    BirdLife Red List Team

  4. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2020 Red List would be to list Caroline Ground-dove as Endangered under Criterion C2a(i); D.

    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.

    The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  5. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisation for this species has not changed. Caroline Ground-dove is recommended to be listed as Endangered under Criteria C2a(i); D.

    Many thanks for everyone who contributed to the 2020 GTB Forum process. The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.