Tagula White-eye (Zosterops meeki) is confined to Tagula (= Sudest) Island (c. 800 km2) in the Louisiade Archipelago of Papua New Guinea. The species has been recorded from sea level (Mitchell 2017) to Mt Riu, the highest point of Tagula, at 801 m, but it has been mostly recorded at middle elevations over 120 m (W. Goulding in litt. 2016). It has primarily been recorded in the forested interior, but has been seen in mangrove and in secondary regrowth behind the littoral zone (Mitchell 2017).
Logging has degraded some of the lowland forest on Tagula (Beehler 1993). In 2019, there were plans to commercially log forest between Reuwo on the south coast and Rambuso Creek on the north coast. This includes primary habitat for this species, in which it has been observed. Associated roads have also been discussed, which would dissect the island between these two points (W. Goulding in litt. 2020). Shifting agriculture causes small areas of forest loss at lower altitudes, although these areas are then left to regrow. From 2008-2018, approximately 2% of forest with at least 50% canopy cover was lost across Tagula (Global Forest Watch 2020). Local human population growth may lead to future impacts through more forest clearance for agriculture (Goulding et al. 2019). Gold prospecting is occurring and mining is a potential threat. Cyclones can cause landslides and damage the forests (Mitchell 2017), and are expected to increase in intensity owing to climate change.
Until recently, very little has been known about the species’s range, population size and threats, and so Tagula White-eye has been listed as Data Deficient. Following surveys on Tagula, more information on these subjects is now known. 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 White-eye has been estimated to be 2.44 years (Bird et al. 2020)*. Hence, reductions are here quantified over a period of ten years.
There is no population data from which to directly estimate trends. From 2008-2018, approximately 2% of forest with at least 50% canopy cover was lost across Tagula, but the rate of forest loss was lower at higher elevations (Global Forest Watch 2020), so the overall rate of forest loss within the species’s range is expected to have been lower than this number. Assuming that the species has been affected by this low level of deforestation over the past ten years, the population size is suspected to have undergone a small reduction of 1-5%. Tagula White-eye is assessed as Least Concern under Criterion A2.
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 a third of the species’s habitat, but it is unlikely that Tagula White-eye would be completely eliminated from the area of logging. Over the next ten years (and probably also over ten years from 2019), the population is suspected to undergo a reduction of 1-29%. This could qualify the species for assessment as Least Concern or as Near Threatened, approaching the threshold for listing as threatened under Criterion A3c+4c, depending on whether logging plans are likely to go ahead, and on how much the population size is likely to be affected as a consequence.
Criterion B – Based on the area of a minimum convex polygon around the range, the Extent of Occurrence (EOO) is estimated to be 1,100 km2. This meets the initial threshold for Endangered under Criterion B1.The Area of Occupancy (AOO) has not been quantified, but based on a 4 km2 grid placed over the approximate area of habitat above 120 m asl within the range, the AOO must be smaller than 576 km2. Since this is close to the threshold for Endangered (<500 km2) and under the assumption that it is unlikely that the whole of this area is occupied, the AOO may be considered likely to fall beneath 500 km2, and so the AOO would meet the initial threshold for Endangered under Criterion B2.To list the species as threatened under Criterion B, at least two further conditions a-c must be met.
Tagula White-eye 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). The species is threatened by forest loss and degradation, which have been progressing slowly, although there are plans for a large logging operation (W. Goulding in litt. 2020). Although the logging could affect up to a third of the range, the species is likely to have some degree of tolerance of logging. Nevertheless, based on the threat of logging, the species could be considered to have fewer than five locations, which would meet the threshold for Endangered for condition a. 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 whole population, then the species may have just one or two locations. However, cyclones are common to the region and the species may be fairly resilient to cyclones. Ongoing logging is degrading the forest within the range, and data on tree cover loss indicates a loss of 1-2% of tree cover with at least 50% canopy cover within the range from 2008-2018 (Global Forest Watch 2020). The species’s response to habitat disturbance is not known, so the population size may not be declining. If the habitat degradation is likely to have an impact on the population size, then there may be a continuing decline in habitat quality and/or area.
The EOO and AOO fall beneath the threshold for listing as Endangered, but it is not clear whether two of conditions a-c are met. If there are only five or fewer locations and there is a continuing decline in habitat quality, the species may qualify as Endangered under Criteria B1ab(iii)+2ab(iii). If either of these conditions is not met, the species may qualify as Vulnerable or Near Threatened under Criteria B1ab(iii)+2ab(iii). We are seeking information on the potential impact of these threats on the population size.
Criterion C – Six to ten individuals were seen in a 6.13 km walk through forest at 120-300 m (W. Goulding in litt. 2016). Assuming that this species could be detected up to about 20-25 m on either side, this might equate to very approximately 20-46 individuals per km2 (W. Goulding in litt. 2020). The area of the island is 813 km2, but although there have been records from sea level (Mitchell 2017), the species has been mostly recorded in forest above an elevation of 120 m (W. Goulding in litt. 2020), which may give an area of habitat of 279 km2 (W. Goulding in litt. 2016). Based on an area of 279-813 km2 of available habitat and the population densities above, the population size is estimated to be between 5,580-37,398 individuals, which roughly equates to 3,720-24,932 mature individuals, here rounded to 3,700-25,000 mature individuals. Since there have been few records below 120 m and the area of habitat is estimated to cover only around a third of the area of the island (W. Goulding in litt. 2016), the true value is likely to fall towards the lower end of this range, and is suspected to be around 5,000 mature individuals (W. Goulding in litt. 2020). This meets the initial threshold for Vulnerable under Criterion C.
For a species to be assessed as threatened under Criterion C, a continuing decline in population size must be observed, estimated, projected or inferred. Although there is ongoing forest loss within the range, this has been proceeding at a slow rate of c. 2% over the last decade, and at an even slower rate at the higher elevations that Tagula White-eye prefers. The species’s tolerance of disturbance is not well known and it is unclear whether this degree of habitat loss would have caused a population decline. There is a plan for a commercial logging operation in the future (W. Goulding in litt. 2020), which may occupy up to a third of the range, but it is uncertain whether this will go ahead, and if it does, what the affect (if any) on the population size will be. In conclusion, although we may suspect that a population decline is taking place, currently it does not appear that there is enough evidence from which to infer a decline. Therefore, the species cannot be assessed as threatened under Criterion C.
There is no estimated or projected rate of population decline from which to assess the species under subcriterion 1. The species does not meet the threshold for subcriterion 2a(i), but it has a single subpopulation, so it would meet subcriterion 2a(ii). There are no extreme fluctuations in the number of individuals. Tagula White-eye is therefore assessed as Near Threatened, approaching the threshold for listing as threatened under Criterion C2a(ii).
Criterion D – Based on the estimate described above, the population size does not meet or approach the threshold for Vulnerable under Criterion D. Although there may be a small number of locations, there is not a threat that could drive the species to Critically Endangered of Extinct (for example, by destroying 80% of habitat) within five years. Tagula White-eye is assessed as Least Concern under Criterion D.
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.
To allow us to achieve a clearer assessment of the species’s status, the following information is requested:
- How certain it is that the proposed logging operation will go ahead?
- If the logging operation goes ahead, what would be the likely timeframe?
- If the logging operation goes ahead, what would be the likely impact on the species’s population size?
- 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. 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.
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.
Global Forest Watch. 2020. Interactive Forest Change Mapping Tool. Available at: http://www.globalforestwatch.org/.
Goulding, W., Perez, A. S., Moss, P., & McAlpine, C. 2019. Subsistence lifestyles and insular forest loss in the Louisiade Archipelago of Papua New Guinea: an endemic hotspot. Pacific Conservation Biology 25(2): 151-163.
Mitchell, D. K. 2017. First photographs of the endemic Tagula White-eye Zosterops meeki, on Sudest Island (Louisiade Archipelago), Papua New Guinea. Bulletin of the British Ornithologists’ Club 137(2): 156-158.