Principe White-eye (Zosterops ficedulinus): revise global status?

Principe White-eye (Zosterops ficedulinus) is endemic to the island of Príncipe, São Tomé and Príncipe. It was recently split from Sao Tome White-eye (Zosterops feae) (del Hoyo and Collar 2016) and at the time was assessed as Vulnerable under criterion D1 (BirdLife International 2018). It is thought to be restricted to the forested hilly interior of the southern part of the island (van Balen 2018), although there are records from more degraded habitats elsewhere on Príncipe (eBird 2018, R. F. de Lima et al. 2018), and it may potentially use the tallest trees in plantations (van Balen 2018). However, surveys by Dallimer et al. (2012) failed to locate the species in any habitat apart from primary rainforest.

The species is currently assessed as being stable, yet this information from Dallimer et al. (2012) suggests the need for review both due to the apparent habitat degradation/loss on the island (Atkinson et al. 1991), and to make sure that threats are being consistently assessed for forest-dependent species on the island. Therefore, we have assessed the species here against all criteria.

 

Criterion A – The rate of deforestation within the species’s range between 2000 and 2012 was estimated to be 0% (Tracewski et al. 2016, Ł. Tracewski unpublished data). However, this could be an artefact of scaling issues, and there is evidence to suggest that the area of forest may be declining as a result of forest clearance (Atkinson et al. 1991). There are reports of this species outside of its mapped range, in degraded habitat (eBird 2018, R. F. de Lima in litt. 2018), but surveys by Dallimer et al. (2012) failed to find the species in any habitat apart from primary rainforest. Therefore, the species is likely intolerant of habitat degradation and as such may be declining, which would be more consistent with the account for Principe Thrush, Turdus xanthorhynchus. However, we have not got an accurate estimate of either the rate of habitat degradation or the population trend, and so we cannot clearly assess the species against this criterion.

 

Criterion B – The species has a highly restricted range (Extent of Occurrence = 50km2), although confirmation of further records from eBird (2018) would extend this. As it currently stands though, this would meet the threshold value for Critically Endangered under criterion B1. The Area of Occupancy has not been calculated per IUCN guidelines (IUCN Standards and Petitions Subcommittee 2017) but it would still likely at least meet the threshold for Endangered (500km2) under criterion B2. To warrant listing as such though, would require at least two subcriteria to be met.

a) The species is not severely fragmented. It may occur at only a limited number of locations given its restricted range. However, given that a quantitative assessment of habitat loss shows no forest loss between 2000 and 2012 (Tracewski et al. 2016, Ł. Tracewski unpublished data) and the main threat to the species is habitat loss, it is therefore very difficult to accurately assess the number of locations* where the species is found.

b) The spread of small farms on Príncipe and further forest clearance (Atkinson et al. 1991) is likely to have resulted in a decline of the area, extent and or quality of habitat for the species, and likely also is leading to a decline in the species’s population size and potentially its Area of Occupancy. Thus the species may trigger at least subcriteria b(iii) and b(v), and potentially also b(ii).

c) The species is not known to undergo extreme fluctuations and so would not trigger subcriterion c).

Therefore, while there is insufficient firm evidence to list the species as threatened under this criterion, the limited information suggests that it certainly approaches the threshold for listing under a threatened category. Thus, it is proposed that under criterion B the species be listed as Near Threatened under criteria B1ab(ii,iii,v)+B2ab(ii,iii,v).

 

Criterion C – The population size is currently placed in the range 250-999 mature individuals. Given how restricted its range is, the population size could be lower and so we request further comment or information regarding this estimate.

Even though deforestation data suggests that there was no forest loss within its range between 2000 and 2012 (Tracewski et al. 2016, Ł. Tracewski unpublished data), this could be in part due to issues of scaling, and it may be more conservative to assess the species as undergoing a continuing decline given that land privatisation has led to an increase in the number of small farms, with primary and secondary forest being cleared (Atkinson et al. 1991).

Dallimer et al. (2012) failed to find the species in either secondary forest or agricultural land, only locating the species in primary rainforest, suggesting that the species is intolerant of habitat alteration. Therefore, even if its habitat hasn’t been outright destroyed, any degradation of primary forest could lead to the disappearance of this species. Therefore, it may be appropriate to infer that the species is undergoing a continuing decline.

Thus, based on the population size currently held, the species would warrant listing as Endangered under criterion C2a(ii).

 

Criterion D – The population size is currently placed in the range 250-999 mature individuals. Therefore, the species qualifies as Vulnerable under criterion D1. Even though it has a very restricted range, it is uncertain whether it would warrant listing as Vulnerable under criterion D2 due to the uncertainty over the number of locations where the species is found.

 

Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species. Therefore, it cannot be assessed against this criterion.

 

Therefore, it is proposed that Principe White-eye be listed as Endangered under criterion C2a(ii).

Any information on current population size and relative encounter rate would be greatly appreciated, as are comments in support of the proposal, which allow the timely acceptance of the changes outlined. However, 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’ Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic.

 

 

*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).

 

References

Atkinson, P.; Peet, N.; Alexander, J. 1991. The status and conservation of the endemic bird species of Sao Tomé and Príncipe, West Africa. Bird Conservation International 1: 255-282.

van Balen, B. 2018. Principe White-eye (Zosterops ficedulinus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/60225 on 10 May 2018).

BirdLife International. 2018. Species factsheet: Zosterops ficedulinus. Downloaded from http://www.birdlife.org on 28/02/2018.

Dallimer, M.; Parnell, M.; Bicknell, J. E.; Melo, M. 2012. The importance of novel and agricultural habitats for the avifauna of an oceanic island. Journal for Nature Conservation 20(4): 191-199.

del Hoyo, J.; Collar, N. J. 2016. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 2: Passerines. Lynx Edicions and BirdLife International, Barcelona, Spain and Cambridge, UK.

eBird. 2018. eBird: An online database of bird distribution and abundance [web application]. eBird, Ithaca, New York. Available: http://www.ebird.org. (Accessed: February 28, 2018).

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.

IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee.

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.

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