Tagula Honeyeater (Microptilotis vicina): Revise global status?

BirdLife species factsheet for Tagula Honeyeater

Tagula Honeyeater (Microptilotis vicina) occurs on Tagula (= Sudest) Island and Junet (=Panatinani) Island (Goulding et al. 2019a), in the Louisiade Archipelago of Papua New Guinea. It inhabits the canopy and understory in most habitat types from mangroves and disturbed subsistence gardens to undisturbed forest, remnant cloud forest and forest edge, in the lowlands to 800 m (Schodde 1978, Coates 1990, Goulding et al. 2019a).

Logging has degraded some of the lowland forest on Tagula (Beehler 1993). Forests on Junet are under increasing pressure from subsistence agriculture due to growing human populations on Grass and Sabara Islands. However, forest loss within the distribution of this species has been relatively slow from the 1970s-2010s (Goulding et al. 2019b) and it appears to be quite adaptable to disturbance (Goulding et al. 2019a). In 2019, there were plans to commercially log forest on Tagula Island (W. Goulding in litt. 2020). Other potential threats include predation or competition from invasive species (including those that are already present, such as Brown Tree Snake, rodents and cats, and potential future invaders such as Indian Myna), droughts and cyclones. The small Extent of Occurrence of Tagula Honeyeater renders it vulnerable to stochastic environmental events such as droughts and cyclones, both of which may become more frequent due to climate change.

Until recently, very little has been known about the species’s range, population size and threats, and so it has been listed as Data Deficient. Following surveys on Tagula and Junet, more information on these subjects has now been published (Goulding et al. 2019a). Our current information on the species’s conservation status will now be compared to all Red List Criteria:

Criterion A – The generation length of Tagula Honeyeater has been estimated to be 2.98 years (Bird et al. 2020)*. Hence, reductions are here quantified over a period of ten years.

Data on tree cover loss indicates a loss of 2% of tree cover with at least 10% canopy cover within the range from 2008-2018 (Global Forest Watch 2020). The species is tolerant of habitat disturbance and is found in forest edge habitat (Goulding et al. 2019a). In 2019, there were plans for commercial logging between Reuwo on the south coast and Rambuso Creek on the north coast (W. Goulding in litt. 2020). Should it go ahead, this could impact up to approximately 10% of the species’s range. However, due to its tolerance of disturbance (Goulding et al. 2019a), it is unlikely that the species would be eliminated from the area by logging. There is no indication of a population reduction approaching 30% within the last ten years, or over the next decade. Tagula Honeyeater is assessed as Least Concern under this criterion.

Criterion B – Based on the area of a minimum convex polygon around the range, the Extent of Occurrence (EOO) is estimated to be 1,510 km2. This meets the threshold for Endangered under Criterion B1.The Area of Occupancy (AOO) has not been quantified, but based on a 4km2 grid placed over the area of mapped range, must be smaller than 1,240 km2. Given that the species is common across most habitats and at all elevations within its range, the AOO is unlikely to fall below 500 km2. The AOO thus meets the threshold for Vulnerable under Criterion B2.To list the species as threatened under Criterion B, at least two further conditions a-c must be met.

The species is not 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” (IUCN 2012). Tagula Honeyeater is threatened by forest loss and degradation, which have been progressing slowly, although there are plans for a large logging operation on Tagula Island (W. Goulding in litt. 2020). Nevertheless, based on the threat of forest degradation or clearance, there are likely to be more than ten locations. It is unclear how severe the impact of a future cyclone or drought may be on the population. If a cyclone may potentially rapidly reduce the global population, or the population occurring on Tagula, then the species may have just one or two locations. However, cyclones are common to the region; the species has persisted with a large population size and it is known to be tolerant of disturbed habitat, so it is probably fairly resilient to cyclones. The number of locations is therefore likely to be larger than ten.

Ongoing logging is degrading the forest within the range, and data on tree cover loss indicates a loss of 2% of tree cover with at least 10% canopy cover within the range from 2008-2018 (Global Forest Watch 2020). However, the species is tolerant of habitat disturbance and is found in forest edge habitat (Goulding et al. 2019a), so the area and/or quality of habitat for Tagula Honeyeater may not be truly declining. It should be noted that a change in habitat that is unlikely to have a detrimental impact on the population size would not be considered to be a decline in this context.

The EOO falls beneath the threshold for listing the species as Endangered and its AOO falls beneath the threshold for Vulnerable, but two conditions are not met, so the species does not qualify as threatened under this Criterion. Tagula Honeyeater is tentatively assessed as Least Concern under Criterion B. However, if there is evidence to suggest that the potential impact of cyclones could be more severe than is implied above, the number of locations could approach or be lower than 10, and the species could qualify as Near Threatened, approaching the threshold for listing as threatened under Criterion B1a+2a.

Criterion C – The population size has been estimated from population density and tree cover data to be between 53,000 – 85,000 individuals across the two islands in 2016 (Goulding et al. 2019a). However, lower density estimates on the larger Tagula Island support a population closer to 50,000 (Goulding et al. 2019a). The population size is therefore estimated at 50,000 – 85,000 individuals, roughly equating to 33,333-56,667 mature individuals, here rounded to 33,000- 57,000 mature individuals. This does not approach the threshold for listing the species as threatened under Criterion C. The species is assessed as Least Concern under this criterion.

Criterion D – Based on the population estimates described above, the population size does not meet or approach the threshold for Vulnerable under Criterion D. The species is therefore assessed as Least Concern under this criterion.

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 that Tagula Honeyeater (Microptilotis vicina) is listed as Least Concern. However, if there is evidence that the number of locations may approach, or be less than, ten, the species may be listed as Near Threatened under Criteria B1a+2a. Comments on the proposed listing are welcomed. To allow us to achieve a clearer assessment of the species’s status, the following information is requested:

  • What would be the potential impact of a cyclone on the species’s population size?
  • Is the slow ongoing habitat loss/degradation likely to be impacting on the species’s population size?

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

Beehler, B. M. 1993. Biodiversity and conservation of the warm-blooded vertebrates of Papua New Guinea. In: Beehler, B.M. (ed.), Papua New Guinea – conservation needs assessment, pp. 77-121. Biodiversity Support Program, Washington, DC.

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.

Coates, B. J. 1990. The birds of Papua New Guinea, 2: passerines. Dove, Alderley, Australia.

Global Forest Watch. 2020. Interactive Forest Change Mapping Tool. Available at: http://www.globalforestwatch.org/.

Goulding, W., Moss, P. T., & McAlpine, C. A. 2019a. An assessment of the Tagula Honeyeater Microptilotis vicina, a Data Deficient bird species in a Melanesian endemic hotspot. Bird Conservation International doi:10.1017/S095927091900025X: 1-20.

Goulding, W., Perez, A. S., Moss, P., & McAlpine, C. 2019b. Subsistence lifestyles and insular forest loss in the Louisiade Archipelago of Papua New Guinea: an endemic hotspot. Pacific Conservation Biology 25(2): 151-163.

Schodde, R. 1978. The status of endangered Papuasian birds, and Appendix. In: Tyler, M.J. (ed.), The status of endangered Australasian wildlife, pp. 133-145 and 185-206 respectively. Royal Zoological Society of South Australia, Adelaide.

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6 Responses to Tagula Honeyeater (Microptilotis vicina): Revise global status?

  1. Red List Team (BirdLife International) says:

    Global Forest Change data on tree cover loss up to 2019 have now been released and made available via Global Forest Watch. Based on these data, approximately 2% of tree cover with at least 10% canopy cover was lost within the species’s range from 2009-2019 (Global Forest Watch 2020). The above assessment remains unchanged.

  2. Guy Dutson says:

    The Goulding et al. 2019a paper provides solid information to support listing as LC. As noted, the species should be resilient to cyclones at least over long evolutionary time periods. Number of locations could relate to number of locations under threat from logging but there are likely to be many small pockets of customary land which are not logged and the species is probably tolerant of typical logging, so listing as NT based on number of locations seems to be unwarranted.

  3. Robert Davis says:

    I agree with the proposed listing. As Guy notes, the published paper provides good information to support resilience to cyclones and stochastic effects and so far habitat loss would seem to be minimal.

  4. Will Goulding says:

    This species is tolerant of disturbance and from my observations, can withstand cyclone related impacts and forest disturbance. It is regularly observed in habitat that is regularly disturbed for subsistence gardens. It is unlikely that there would be threat, e.g. logging, that would meet the NT number of locations criteria across these islands.

  5. 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

  6. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2020 Red List would be to adopt the proposed classification outlined in the initial forum discussion.

    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 those in 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.

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