BirdLife species factsheet for Rapa Fruit-dove: http://datazone.birdlife.org/species/factsheet/rapa-fruit-dove-ptilinopus-huttoni
The Rapa fruit-dove (Ptilinopus huttoni) is endemic to the tiny island of Rapa in the Tubuai Islands, French Polynesia, where its population was estimated at 274 individuals (175-368) in 1989-1990 (Thibault and Varney 1991). Although it is probable that the area of available habitat has diminished during the 20th century, and this may have caused a decrease in population, in 1991 there was thought to have been no serious decline since 1974 (Thibault and Varney 1991). The situation in 2007 was thought to be much the same (J. Millet in litt. 2007). Due to its very small population, the species is currently listed as Endangered under Criterion D (see BirdLife International 2017).
During 2017, a survey of the Rapa fruit-dove was carried out, using some of the same observation locations as the 1989-90 survey (Blanvillain & Patira 2017). The study estimated the population at 160 (145-243) individuals, based on counts and maps of forested areas produced in 1986, with the caveat that the maps appeared to underestimate the amount of forest present, so the population estimates may be underestimates. The study also indicated that relative to the 1989-90 survey, the population of the Rapa fruit-dove had fallen by 42%. The quality of habitat was also likely to have declined due to invasion of strawberry guava Psidium cattleianum. Therefore, the species has been re-assessed against all criteria based on current best information.
Criterion A – The results of the 2017 survey estimate that the population size has declined by 42%, from 274 to 160 individuals since 1990. This is equivalent to a reduction of 13% over three generation lengths (9.6 years), assuming exponential decline. The species qualifies for listing as Least Concern under Criterion A.
Criterion B – The species’s extent of occurrence (EOO) has been calculated as 30km2, meaning that it falls beneath the threshold for listing as Critically Endangered under Criterion B. For a species to qualify as threatened under Criterion B, at least two of three conditions must also be met. The species is not severely fragmented, but is currently assessed as having only one location. However, based on the IUCN definition of a location as ‘a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present’, and the most serious plausible threats being destruction and degradation of forest by goats, cattle, fires and felling, the number of locations may be better placed in the band of 2-5, satisfying condition a at the level of Endangered. The results of the 2017 survey indicate that the species is undergoing a continuing decline in population size, area of occupancy and quality of habitat, satisfying condition b. The species thus qualifies as Endangered under Criterion B.
Criterion C – Recent surveys have estimated the population size at 160 individuals, with the caveat that this may be an underestimate due to the use of old and inaccurate maps in producing the estimate. Notwithstanding the figure potentially being an underestimate, it appears likely that the total number of mature individuals is less than 250, falling beneath the threshold for Critically Endangered under Criterion C. The estimated rate of continuing decline is equivalent to 9% in 2 generations or 13% in 3 generations, meaning that the species qualifies for listing as Vulnerable under Criterion C1. The species has only one subpopulation, meaning that the species qualifies for listing as Endangered under Criterion C2a(i) and as Critically Endangered under Criterion C2a(ii). The species thus qualifies for listing as Critically Endangered under Criterion C.
Criterion D – Recent surveys have estimated the population size at 160 individuals, with the caveat that this may be an underestimate due to the use of old and inaccurate maps in producing the estimate. Notwithstanding the figure potentially being an underestimate, it appears likely that the total number of mature individuals falls in the band of 50-249, qualifying the species for listing as Endangered under Criterion D.
Criterion E – To the best of our knowledge no quantitative assessment of the probability of extinction has been conducted for the species, and so it cannot be assessed against this criterion.
In conclusion, it is proposed that the Rapa fruit-dove be listed as Critically Endangered under Criterion C2a(ii). We welcome any comments on this proposed uplisting.
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.
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.
BirdLife International (2017) Species factsheet: Ptilinopus huttoni. Downloaded from http://www.birdlife.org on 21/12/2017.
Blanvillain, C. and Patira, P. (2017) Premiers résultats sur l’inventaire 2017 du Koko de Rapa : Ptilope de Hutton, Ptilinopus huttoni, et recommandations pour une classification de l’espèce dans la catégorie en danger critique d’extinction. Société d’Ornithologie de Polynésie « MANU », Tahiti, French Polynesia.
Thibault, J.-C., Varney, A. (1991) Numbers and habitat of the Rapa Fruit-dove Ptilinopus huttoni. Bird Conservation International 1: 75-81.