The Tahiti Monarch (Pomarea nigra) is endemic to Tahiti in the Society Islands, French Polynesia, where it now occurs in an extremely small range in just three valleys (Papehua, Tiapa and Maruapo) in the south-west of the mainland (Gaze & Blanvillain 1998, Blanvillain et al. 2003). In 1998, just 25 birds were located (Blanvillain et al. 2003) and the species has since been listed as Critically Endangered owing to its extremely small population.
The species is threatened by a range of invasive species. It has suffered predation from the Black Rat (Rattus rattus) and the Common Myna (Acridotheres tristis) (Thibault et al. 2002, Blanvillain et al. 2003). Red-vented Bulbul (Pycnonotus cafer) has been implicated in reducing chick survival by disrupting the reproduction of paired Monarchs and competing for food and territories (Thibault et al. 2002, Blanvillain et al. 2003, Ghestemme 2011). Little Fire Ants (Wasmannia auropunctata), a species that predates bird nests and competes with native species for food, recently established three supercolonies eventually covering a total of 70 ha at the entrances of the valleys where the monarch is found (SOP-Manu 2018). The monarch’s forest habitat is now largely composed of introduced invasive species such as Miconia calvescens and the African tulip tree (Spathodea campanulata), which have substantially modified the forest structure and ecology (Blanvillain et al. 2013). Goat grazing has also led to habitat degradation and monarch population declines in one of the range valleys (Ghestemme 2009, Blanvillain et al. 2013). Other threats faced by the species include predation by cats and Swamp Harrier (Circus approximans) (Ghestemme 2009) and potentially an increase in extreme weather events due to climate change (Blanvillain et al. 2020).
Since 1998, extensive conservation work has been undertaken to restore the Tahiti Monarch. Rat control began in 1998 (Blanvillain 2000) and has continued since, substantially reducing the level of predation by rats (Blanvillain et al. 2013). An extensive control programme against Common Myna and Red-vented Bulbul has been performed since 2000. This has led to the removal of thousands of birds, the elimination of the Common Myna and an increased nesting success of the Tahiti Monarch (Blanvillain et al. 2020). Control of Little Fire Ant has also been undertaken. Following control measures, the area of the colonies was reduced by 85% by the end of 2018 (SOP-Manu 2018, Blanvillain 2019, Blanvillain et al. 2020). Regular and extensive control of invasive Miconia and Tulip Tree is ongoing within the range (Raust 2010, Blanvillain et al. 2013). Other habitat restoration work has included propagating native mara trees and other indigenous plants in the field and in a nursery (Blanvillain et al. 2013, 2015, SOP-Manu 2018). Efforts have been made to provide enclosures for goats and pigs in the Maruapo valley and thereby to prevent them from causing habitat degradation (Blanvillain et al. 2013).
As a result of this considerable conservation effort, the Tahiti Monarch’s population size has increased. In 2018 the population size was estimated at 79 adults (Blanvillain 2019, Blanvillain et al. 2020), followed by an estimated 91 adults in 2019 (C. Blanvillain in litt. 2020). Following this population increase, the species may no longer qualify for Critically Endangered under Criterion D. Hence, we are undertaking a review of the species’s Red List Category. Our current information on the species’s conservation status will now be compared to all Red List Criteria.
Criterion A – The generation length of Tahiti Monarch has recently been re-estimated at 3.33 years (Bird et al. 2020)*. Hence, population reductions should be assessed over a period of ten years for the application of Criterion A.
In the ten years since 2010, the population of Tahiti Monarch has increased. There is no evidence to suggest that the population size will undergo a reduction over the next ten years. The species is assessed as Least Concern under Criterion A.
Criterion B – The Extent of Occurrence (EOO), inferred from the area of a minimum convex polygon around the mapped range, is estimated at 4 km2 (please note that the range map has been updated for this assessment, based on the map shown in Blanvillain et al. 2018). This meets the initial threshold for Critically Endangered under Criterion B1. Based on a grid of 4 km2 squares placed over the mapped range, the Area of Occupancy (AOO) is estimated at 20 km2. However, when an AOO estimate is larger than the estimated EOO, the AOO should be revised downwards to match the EOO. Hence, the Area of Occupancy is also estimated as 4 km2. This meets the initial threshold for Critically Endangered under Criterion B2.To list the species as threatened under Criterion B, two further conditions a-c must be met.
Condition a relates to severe fragmentation or a small number of locations. ‘A taxon can be considered to be severely fragmented if most (>50%) of its total area of occupancy is in habitat patches that are (1) smaller than would be required to support a viable population, and (2) separated from other habitat patches by a large distance’ (IUCN Standards and Petitions Committee 2019). Although the Tahiti Monarch’s population is distributed across three valleys, they are close together, and an individual transferred from Maruapo to Tiapa in 2009 was found to have moved back to its original territory in Maruapo in 2012 (Blanvillain et al. 2013). It is therefore unlikely that the three valley populations are isolated subpopulations, and hence the species is not considered to be severely fragmented. ‘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 […]. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat’ (IUCN 2012). There is no plausible threat that is likely to rapidly (i.e. within 3 years) affect the entire population, so the species has more than one location. The most serious plausible threats to the Tahiti Monarch are predation by Black Rat and Common Myna, and competition with Red-vented Bulbul. The cessation of rat control in the upper Maruapo valley led to a population decline from 33 to 12 individuals over seven years (Blanvillain et al. 2013, 2020). This rate of decline is equivalent to a 60% reduction over a generation (3 years). It is therefore plausible that the number of locations could be within the range 2-5, which meets condition a at the level of Endangered.
Condition b relates to a continuing decline. The population size is increasing, and there is no evidence that its EOO, AOO or number of locations or subpopulations are currently declining. Condition b could be met if there was evidence that the extent or quality of habitat is declining. The species’s forest habitat is degraded by invasive species, including Miconia and Tulip Tree. However, there have been substantial efforts made to control these invasive plants and to propagate the native mara tree within the Tahiti Monarch’s range (Raust 2010, Blanvillain et al. 2013, 2015, SOP-Manu 2018). Goat grazing has previously led to habitat degradation and population declines in the Maruapo valley (Ghestemme 2009, Blanvillain et al. 2013), but efforts have been made to provide enclosures to prevent them from causing further habitat degradation (Blanvillain et al. 2013). We therefore tentatively consider that the Tahiti Monarch’s habitat is not undergoing a continuing decline in extent or quality. This assertion is supported by the ongoing trend in the population size. Therefore, condition b is not met.
Condition c relates to extreme fluctuations. There is no evidence that the species’s population or range size are undergoing extreme fluctuations. Condition c is not met.
In conclusion, although the EOO and AOO both fall beneath the thresholds for listing the species as Critically Endangered under Criterion B, condition a is met only at the level of Endangered, and neither condition b nor c is met. Therefore, Tahiti Monarch is assessed as Near Threatened, approaching a threatened status under Criterion B1a+2a.
If however, evidence is provided to indicate that the habitat is undergoing a continuing decline in quality and/or extent, the species would quality as Endangered under Criteria B1ab(iii)+2ab(iii). If, in addition, there evidence is provided to indicate that there is a plausible threat that could rapidly affect the species’s entire population, then the species would qualify as Critically Endangered under Criteria B1ab(iii)+2ab(iii).
Criterion C – Although the species has a very small population size, it is not undergoing a continuing decline. Tahiti Monarch is assessed as Least Concern under Criterion C.
Criterion D – In 2014, there were an estimated 43 territorial adults, plus at least ten more non-territorial birds (Blanvillain et al. 2015), fledging 12 young (LPO 2014). In 2015, 53 adults (but only 13 breeding pairs) fledged 14 young (Blanvillain et al. 2018). The population size has continued to rise, and in 2018 the population size was estimated at 79 adults (Blanvillain 2019, Blanvillain et al. 2020), followed by an estimated 91 adults in 2019 (C. Blanvillain in litt. 2020). The population size is therefore placed in the band 50-100 mature individuals. This meets the threshold for Endangered under Criterion D.
For a species to be downlisted to a lower category of threat on the IUCN Red List, the species should not have qualified for the higher category for at least five years. This means that, to down-list the Tahiti Monarch to Endangered in 2020, the species would need to have had a population size of at least 50 mature individuals since 2015 at the latest. Based on the figures provided above, and the population graph presented in Blanvillain et al. 2020, this requirement is met.
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, it is proposed to list the Tahiti Monarch (Pomarea nigra) as Endangered under Criterion D. However, should evidence arise that indicates that the species has only one location AND a continuing decline in habitat quality, the species may be retained asCritically Endangered under Criteria B1ab(iii)+2ab(iii). Alternatively, should evidence arise that the species has not had a population size of at least 50 mature individuals for at least five years, the species may be retained as Critically Endangered under Criterion D.We welcome any comments to the proposed listing. Information is particularly requested on the potential scale of impact of plausible threats, ongoing trends in the habitat quality and extent, and the population size over the past five years.
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.
Bird, J. P., Martin, R., Akçakaya, H. R., Gilroy, J., Burfield, I. J., Garnett, S. G., Symes, A., Taylor, J., Şekercioğlu, Ç. H. and Butchart, S. H. M. 2020. Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.
Blanvillain, C. 2000. Programme de sauvegarde du monarque de Tahiti: des premiers résultats prometteurs pour la survie de l’espèce. Bulletin de la Société d’Ornithologie de Polynésie (Te Manu) 30: 3-4.
Blanvillain, C. 2019. Caroline Blanvillain’s accomplishments that have resulted in a demonstrable positive impact on several animal species that is likely to improve the species likelihood of long-term sustainability.
Blanvillain, C., Ghestemme, T, and O’Brien, M. 2013. Tahiti Monarch Action Plan (Pomarea nigra) 2013-2017. Société d’Ornithologie de Polynésie, SOP Manu, Taravao, Tahiti, French Polynesia.
Blanvillain, C., Ghestemme, T., Saavedra, S., Yan, L., Michoud-Schmidt, J., Beaune, D., & O’Brien, M. 2020. Rat and invasive birds control to save the Tahiti monarch (Pomarea nigra), a critically endangered island bird. Journal for Nature Conservation 55: 125820.
Blanvillain, C., Yan, L., Michoud-Schmidt, J., Butaud, J.F., Brodien, I., Cornu, T., Henneberg, C., Tairio, T., Petit, A., Portier, E. et Ghestemme, T. 2015. Programme de conservation du Monarque de Tahiti: Bilan des actions de l’annee 2014. Te Manu 85: 5-11.
Blanvillan, C., Ghestemme, T., Withers, T. and O’Brien, M. 2018. Breeding biology of the Critically Endangered Tahiti Monarch Pomarea nigra, a bird with a low productivity. Bird Conservation International 28: 606-619.
Gaze, P. and Blanvillain, C. 1998. Report to Societe d’Ornithologie de Polynesie on the Tahiti monarch (Pomarea nigra) .
Ghestemme T. 2011. Impacts of introduced birds on the last population of the Tahiti Monarch. Pacific Invasive Initiative newsletter.
Ghestemme, T. 2009. Le Monarque de Tahiti rajeunit mais les martins-chasseurs l’empêchent de s’établir. Te Manu: 3-4.
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
IUCN Standards and Petitions Committee. 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.
LPO. 2014. Les Monarques ne veulent pas s’éteindre. L’Oiseau Magazine 117: 36.
Raust, P. 2010. Le Monarque de Tahiti de la vallée Maruapo. Te Manu: 3-4.
SOP-Manu. 2018. Te Manu iti.
Thibault, J. C.; Martin, J. L.; Penloup, A.; Meyer, J. Y. 2002. Understanding the decline and extinction of monarchs (Aves) in Polynesian Islands. Biological Conservation 108: 161-174.