Santa Cruz Ground-dove (Alopecoenas sanctaecrucis): revise global status?

In the most recent Red List assessment for Santa Cruz Ground-dove (Alopecoenas sanctacrucis) the species was considered to occur on only two islands – the volcanic island of Tinakula, Solomon Islands, and Espiritu Santo, Vanuatu; with the species thought to be probably extinct on Utupua, and historically thought to occur on even more islands (BirdLife International 2017). It is currently listed as Endangered under criterion B1ab(ii,iii,v), but in 2017 its Extent of Occurrence (EOO) was recalculated using a Minimum Convex Polygon, with the result that the species no longer qualifies for listing under its current Red List category.

We previously proposed changing the Red List category of Santa Cruz Ground-dove (among other species) on the basis of its revised EOO in a forum topic posted in 2017 (available here). However, the species’ situation has changed over the course of 2017, and as such we have created this new forum topic to allow discussion this species’ global status in light of newer information (please note that comments discussing this species will now only be accepted under this topic).

In 2017 trappers went to Tinakula and collected a large number of individuals from the population there, some of which ended up in the cagebird market, although some were confiscated in the Solomon Islands before they could leave the country (N. Collar in litt. 2017). Then in October, the Tinakula volcano erupted, destroying a large part of the island, and potentially killing a large proportion of the population of this species on the island (N. Collar in litt. 2017).

A survey took place in mid-December on Tinakula and this managed to find some individuals still living in the wild on the island. In total this survey located only 11 male and 4 female Santa Cruz Ground-doves (which could potentially equate to the whole population on the island), while 109 individuals rescued from trade are now being safely kept in captivity in the Solomon Islands (per OceansWatch Facebook page https://www.facebook.com/oceanswatch/, Assomull 2017). The species is not restricted to Tinakula, although sightings on Espiritu Santo are rare, with recent records only coming from 1972, 1985, two sightings of one to two birds in 2006 (Barré et al. 2011) and individuals heard in both 2008 and 2009 (G. Dutson in litt. 2009). However, given the worrying situation on Tinakula we have reassessed the species here against all criteria.

 

Criterion A – With the recent situation on Tinakula we can say that there has been a one-off large reduction in the population size. However, the uncertainty over the population found on Espiritu Santo means that it is very difficult to clearly assess the overall declines in the population. Therefore, we cannot accurately assess the species against this criterion.

 

Criterion B – Use of the Minimum Convex Polygon method to calculate EOO (per IUCN 2001, 2012, Joppa et al. 2016) led to the proposal for this species to be downlisted from Endangered to Vulnerable under criterion B2 in 2017 (see here). With the first surveys on Tinakula after the eruption showing that the species does persist there (albeit at a potentially tiny population size) the proposal to alter the species’ listing under this criterion alone should still stand. Therefore, looking at only criterion B, the species warrants listing as Vulnerable under criterion B2ab(ii,iii,v).

 

Criterion C – While the eruption of Tinakula has caused a large one-off population reduction, any remaining population on Espiritu Santo is also likely to be undergoing a continuing decline due to the ongoing threats of introduced mammals and habitat loss.

The population size is currently listed as 600-1,700 mature individuals, although the population size is probably now smaller than this as a result of the losses from Tinakula, and given that it was only a rough estimation, the population size may have been smaller than this in the first place. As the species is so rarely recorded on Espiritu Santo the population size there could be very small, but given how recent the latest record is from Espiritu Santo we cannot outright say that the species is no longer found there. Therefore, using the lowest population densities of former congeners (genus Gallicolumba) and assuming only a proportion of its range there is occupied would give a population size for Espiritu Santo in the range 210-1,055 mature individuals.

The recent survey on Tinakula found 15 individuals – 11 males and 4 females, although it is not certain whether these were all mature individuals (although Baptista et al. [2018] do describe a different plumage colouration in juveniles, so it is possible that all counted individuals may be mature); and it is not known whether this is the total population for the island, or whether there may be some other individuals present still. The skew in the sex ratio of individuals found means that a lower population size should be used (per IUCN Standards and Petitions Subcommittee 2017), but again it is unknown whether it is possible for all individuals in this very small population to successfully breed. Given the uncertainty, it is very tentatively suggested that the population size for Tinakula be assessed as 8-15 mature individuals. This would then give an overall global population in the range 218-1,070 mature individuals, which therefore falls at the boundary for the threshold for Critically Endangered under criterion C.

The rate of continuing decline is not known, so we cannot assess the species against criterion C1, and the species is not known to undergo extreme fluctuations so it wouldn’t warrant listing under criterion C2b. From the above rough population estimates for the two islands, the largest subpopulation contains >50 mature individuals, so it would not warrant listing as Critically Endangered under criterion C2a(i), but it may contain <250 mature individuals. Therefore, the species could precautionarily be listed as Endangered under criterion C2a(i).

Regarding criterion C2a(ii), to be listed as Critically Endangered under this criterion would require >90% of the population to be found in 1 subpopulation, along with meeting the threshold population size. At the lower end of the population size range, this is the case, and so Santa Cruz Ground-dove may warrant listing as Critically Endangered under criterion C2a(ii). This is, of course, if we accept the rough population estimates. If there were to be more individuals found on Tinakula it is plausible that the species would not even meet the conditions for listing as Endangered under criterion C2a(ii) as the largest subpopulation would need to contain >95% of the global population, and indeed a population size range of 250-999 mature individuals may in fact be more appropriate based on this uncertainty. On the other hand, the population size on Espiritu Santo could be even smaller than we have estimated here, and so the global population size range could in turn be even smaller, with knock-on consequences for the assessment against this criterion. Therefore, further information is required before a clear assessment can be made against this criterion.

 

Criterion D – With the tentative population size estimate of 218-1,070 mature individuals, the species would meet the population size threshold for Endangered under criterion D, using the lowest population size estimate, or could be considered Near Threatened under the same criterion at the higher end of the estimate, as it would approach, but not meet the threshold for Vulnerable. Using a precautionary approach, the species could be listed as Endangered under criterion D. It does have a limited range but it is uncertain whether the threats on Espiritu Santo are sufficiently great that it may go extinct within a very short period of time (1-2 generations or c.6.5-13 years). Therefore, it is tentatively not considered to warrant listing under criterion D2, although further comments are welcome.

 

Criterion E – To the best of our knowledge there has been no quantitative analysis of extinction risk for this species. Therefore, it cannot be assessed against this criterion.

 

Therefore, there is evidence to tentatively suggest that the species could be maintained as Endangered under criteria C2 and D, or even uplisted to Critically Endangered under criterion C2a(ii). However, before a clearer re-assessment is possible, further information and comments are urgently requested, particularly regarding the population size on Espiritu Santo. Please note though that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are relevant to the information that is sought, or about the species’ Red List status.

 

References

Assomull, S. A. 2017. Endangered birds rescued from wildlife trade by Singaporean. The Straits Times December 29 2017: http://www.straitstimes.com/singapore/endangered-birds-rescued-from-wildlife-trade-by-sporean

Baptista, L. F.; Trail, P. W.; Horblit, H. M.; Christie, D. A.; Kirwan, G. M.; Boesman, P. 2018. Santa Cruz Ground-dove (Alopecoenas sanctaecrucis). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/54270 on 9 January 2018).

Barré, N., Delsinne, T. and Fontaine, B. 2011. Terrestrial Bird Communities. In: Bouchet P., Le Guyader H. and Pascal O. (eds), The Natural History of Santo, MNHN, IRD, PNI, Paris.

BirdLife International. 2017. Species factsheet: Alopecoenas sanctaecrucis. Downloaded from http://www.birdlife.org on 15/12/2017.

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. Available at: www.iucnredlist.org/technical-documents/categories-and-criteria.

IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Joppa, L. N.; Butchart, S. H. M.; Hoffmann, M.; Bachman, S. P.; Akçakaya, H. R.; Moat, J. F.; Böhm, M.; Holland, R. A.; Newton, A.; Polidoro, B.; Hughes, A. 2016. Impact of alternative metrics on estimates of extent of occurrence for extinction risk assessment. Conservation Biology 30: 362-370.

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One Response to Santa Cruz Ground-dove (Alopecoenas sanctaecrucis): revise global status?

  1. Mark OBrien says:

    Bird reported sighted on two occasions on the slopes of Mt Tabwesawema, Espiritu Santo in late 2017/early 2018 by Vanuatu government environment staff. This mountain peak has just been listed as a Community Conservation area – so more effort to monitor the area is likely. There is very little survey effort for the majority of the Cumberland Range in Santo other than at Santo Peak where a number of visits certainly have drawn a blank on this species.

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