BirdLife Species factsheet for San Cristobal Dwaf-kingfisher: http://datazone.birdlife.org/species/factsheet/san-cristobal-dwarf-kingfisher-ceyx-gentianus
San Cristobal Dwarf-kingfisher (Ceyx gentianus) has been recently split from C. lepidus and is restricted to the island of Makira (formerly San Cristobal) in the Solomon Islands. The species can be found in forested habitats, which need not be near watercourses, and is tolerant of some habitat degradation like other members of its genus (Buckingham et al. 1990; G. Dutson in litt. 2016, del Hoyo et al. 2001). The species is currently listed as Near Threatened under criterion D2 (BirdLife International 2017), on the precautionary basis that invasives such as the brown tree-snake (Boiga irregularis) could cause some rapid future declines. That said, B. irregularis is native to the Solomon Islands, despite not being known from the Makira area, and the potential impact of the snake may have been overestimated. Therefore, the species may warrant downlisting.
Despite the species being tolerant of habitat degradation, there is continuing forest loss on Makira as a result of subsistence farming and industrial logging (G. Dutson in litt. 2016). However, the rate of forest loss across its range is low (data from Tracewski et al. 2016) and so if any declines are taking place they are likely to be very slow. Therefore, the species does not approach the threshold for Vulnerable under criterion A. Additionally, the species would not approach the threshold for Vulnerable under criterion B either because despite occurring on one small island (Extent of Occurrence = 3,300km2) where habitat area/quality may be declining, its habitat is neither restricted to a limited number of locations* nor severely fragmented, with no extreme fluctuations in habitat or population size.
Encounter rates of this species were recorded at 30-90 birds per km2 by Buckingham et al. (1990), which would roughly equate to 20-60 mature individuals per km2, and subsequent field work on the island appears consistent with these densities (Danielsen et al. 2010, G. Dutson in litt. 2016). Therefore, conservatively assuming only a proportion of its range is occupied, the population size of this species would fall in the range 10,000-30,000 mature individuals. Therefore, the species would not approach the threshold for Vulnerable under criterion D. However, the lower end of the population estimate would approach the threshold for Vulnerable under criterion C2a(ii), and so it might warrant retaining as Near Threatened under this criterion if the species is considered to be declining.
Therefore, we request any further information or comments on this species, particularly regarding the potential for a decline and how much of its habitat it may occupy as these are key parameters for deciding whether this species remain as Near Threatened, or whether it would warrant downlisting to Least Concern.
*Note that 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. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).
BirdLife International. 2017. Species factsheet: Ceyx gentianus. Downloaded from http://www.birdlife.org on 23/05/2017.
Buckingham, D. L.; Dutson, G. C. L.; Newman, J. L. 1990. Birds of Manus, Kolombangara and Makira (San Cristobal) with notes on mammals and records from other Solomon Islands. Report of the Cambridge Solomons Rainforest Project 1990. Official Cambridge Expedition Charity no. 311460.
Danielsen, F.; Filardi, C. E.; Jønsson, K. A.; Kohaia, V.; Krabbe, N.; Kristensen, J. B.; Moyle, R. G.; Pikacha, P.; Poulsen, M. K.; Sørensen, M. K.; Tatahu, C.; Waihuru, J.; Fjeldså, J. 2010. Endemic avifaunal biodiversity and tropical forest loss in Makira, a mountainous Pacific Island. Singapore Journal of Tropical Geography 31: 100-114.
del Hoyo, J.; Elliott, A.; Sargatal, J. 2001. Handbook of the birds of the world, Vol 6: Mousebirds to Hornbills. Barcelona, Spain: Lynx Edicions.
IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. Gland, Switzerland and Cambridge, UK: IUCN Species Survival Commission.
IUCN. 2012. Guidelines for Application of IUCN Red List Criteria at Regional and National Levels: Version 4.0. Gland, Switzerland and Cambridge, UK: IUCN.
Tracewski, Ł.; Butchart, S. H. M.; Di Marco, M.; Ficetola, G. F.; Rondinini, C.; Symes, A.; Wheatley, H.; Beresford, A. E.; Buchanan, G. M. 2016. Toward quantification of the impact of 21st-century deforestation on the extinction risk of terrestrial vertebrates. Conservation Biology 30: 1070-1079.