Principe Speirops (Zosterops leucophaeus): revise global status?

This discussion was first published as part of the 2018 Red List update. At the time a decision regarding its status was pended, but to enable potential reassessment of this species as part of the 2019 Red List update this post remains open and the date of posting has been updated.

Principe Speirops (Zosterops leucophaeus) is endemic to the island of Príncipe, São Tomé and Príncipe, and is currently listed as Near Threatened (BirdLife International 2018). It is considered to be a forest species, and as such has been considered to be undergoing a continuing decline as a result of habitat loss and degradation due to agriculture. Pesticide use in plantations was also thought to have contributed to declines, particularly between the 1970s and 1990s (Atkinson et al. 1991).

However, the species is not restricted to primary forest. It may actually be more commonly found in forest regrowth, as well as occurring in plantations and other agricultural land (Dallimer et al. 2012, van Balen 2018), and other evidence suggests population densities may not be very different between primary and secondary forest and agricultural land (Dallimer et al. 2012). Therefore, the species may not be suffering a continuing decline, and even if it is then the rate of decline may be very small.

Additionally, while one of the criteria it is currently listed under is C2a(ii) (small and declining population) the species may not be that rare. In van Balen (2018) the species is considered “frequent to common but somewhat local”, and Dallimer et al. (2012), based on population densities, have the species in top four most common species on Príncipe for primary forest, secondary forest and agricultural land (although all starling species were lumped into ‘starlings’). Additionally, the species may be similar in abundance to several Príncipe endemic species; Principe Golden Weaver (Ploceus principes), Principe Sunbird (Anabathmis hartlaubii) and Dohrn’s Warbler (Sylvia dohrni) (R. F. de Lima in litt. 2018) which are all currently Least Concern.

Therefore, given this evidence, we have reviewed the species’s status here against all criteria.

 

Criterion A – While the species is currently listed as decreasing due to habitat destruction and fragmentation, it appears to show very similar population densities for this species across primary forest, secondary forest and agricultural land (see Fig. 4 in Dallimer et al. 2012). Therefore, even if the species is very tentatively listed as decreasing it would not approach the threshold for Vulnerable under this criterion (reduction of 30% over 3 generations or 10 years).

 

Criterion B – The species does have a restricted range (Extent of Occurrence = 200km2), and there is some ongoing conversion of its favoured habitat to agricultural land, suggesting a continuing decline in the area/quality of habitat. However, the species does show very similar population densities in primary and secondary forest as well as agricultural land (Dallimer et al. 2012) so it is uncertain to what extent we can say there is a decline in the quality of the species’s habitat. Additionally, the species is not thought to undergo extreme fluctuations; its range is not severely fragmented; and given that habitat loss/degradation is the main threat, the species is likely to be found at >>10 locations*. Therefore, it would not warrant listing under this criterion.

 

Criterion C – Given its restricted range, the population size of this species is unlikely to be large, and potentially falls below the threshold for Vulnerable (10,000 mature individuals). However, descriptions of its abundance suggest that it is not rare, and it does appear to be as frequently seen and as common as other species found on Príncipe, that are currently listed as Least Concern (R. F. de Lima in litt. 2018).

The fact that it is found at roughly similar densities in primary forest as secondary forest and agricultural land (Dallimer et al. 2012), also suggests it may not be undergoing a continuing decline. Therefore, given this evidence it may be appropriate to say that the species does not warrant listing under this criterion. If we were to still suspect a very slow decline, it would likely then warrant listing as Near Threatened under criterion C2a(ii).

 

Criterion D – Even though it has not been quantified, the population size is suspected to not approach the threshold for Vulnerable under criterion D1, and the species is not found at few enough locations* to warrant listing under criterion D2.

 

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 tentatively proposed that Principe Speirops be downlisted to Least Concern unless there is further evidence to suggest that we should continue to assess the species as declining. If such evidence were forthcoming then the species would likely warrant to retain a listing as Near Threatened under criterion C2a(ii). We welcome comments and further information, including those expressing support as these help us to accept a proposal.

 

 

*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.

BirdLife International. 2018. Species factsheet: Zosterops leucophaeus. Downloaded from http://www.birdlife.org on 27/02/2018.

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.

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.

van Balen, B. 2018. Principe Speirops (Zosterops leucophaeus). 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/60254 on 27 February 2018).

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3 Responses to Principe Speirops (Zosterops leucophaeus): revise global status?

  1. Alan Tye says:

    Regarding criterion VU (D2), all depends on the definition of location, with respect to potential threats. The species could be susceptible to an introduced predator or pathogen capable of existing across the whole island, in which case the number of locations would effectively be one. In such a case, the species could be considered as meeting the criteria for VU (D2)

  2. Ricardo Faustino de Lima says:

    I agree with Alan Tye regarding the application of the concept of location. Anyway, for the sake of consistency, if this species is to be classified as VU so should all other Príncipe endemics that have similar abundances, distributions and habitat associations. This seems rather drastic. Alternatively, they could all be classified as NT.

    An extensive survey of the island’s biodiversity is currently underway, led by the Príncipe Trust, in collaboration with BirdLife International. This is similar to the survey that took place in Sao Tome, and will certainly help making better informed decisions in future assessments. Until then, I would agree with keeping this species (and those in a similar situation) as LC, namely because Príncipe has recently been classified as a UNESCO Biosphere Reserve and there is a strong compromise by the regional government to attain a model of sustainable development for the island.

  3. James Westrip (BirdLife) says:

    Preliminary proposals

    To define a location requires more than a tentative hypothetical threat, the threat has to be the most serious plausible current threat, or one that is plausible to occur in the near future. To be listed as Vulnerable also requires more than the species to occur at a small number of locations. The threat must impact the species so severely that it would become Critically Endangered or Extinct within a very short period of time (e.g. one generation – in this case c.4 years). The guidelines also specify that non-specific events like an unspecified disease do not qualify a species for listing as Vulnerable under criterion D2.

    Thus, to allow time for further comment, the preliminary decision for this topic is to pend a decision until 2019 and so retain the current listing as part of the 2018 Red List update.

    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 the initial proposal.
    The final 2018 Red List categories will be published on the BirdLife and IUCN websites in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

    Reference:
    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. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

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