Giant Sunbird (Dreptes thomensis): revise global status?

Giant Sunbird (Dreptes thomensis) is endemic to São Tomé, São Tomé and Príncipe. A predominantly primary forest species, it occurs in both lowland and montane forest up to 2,000m, although with some records from the forest-edge of cultivated areas and plantations (see BirdLife International 2018b, Cheke and Mann 2018). The species is currently listed as Vulnerable under criterion D1 on the basis of a very small population size estimate (BirdLife International 2018b).

The primary threat to the species appears to be from habitat loss and degradation. Historically lots of lowland and mid-altitude forest was cleared for plantations, and land privatisation has led to further clearance with the spread of small farms. Cultivation for timber and fuel also appear to threaten forest in the north of the species’s range (Atkinson et al. 1991). Development of roads along the east and west coast of the island have also meant that remote areas are now more accessible, which could increase deforestation rates (A. Gascoigne in litt. 2000). From this information, we would assume that the species should be inferred to be undergoing a continuing decline. However, this currently is not the case. Instead the species is listed as stable, as it was not thought that primary forest was being particularly impacted (A. Gascoigne in litt. 2000).

This could be acceptable as deforestation analyses (Tracewski et al. 2016, Ł. Tracewski unpublished data) suggests there was no deforestation within the species’s range between 2000 and 2012. However, this could just be an artefact of the small scale of the range; habitat degradation may not be fully taken into account in these analyses; and giving Giant Sunbird a population trend of ‘stable’, when it is predominantly dependent on primary forest, is not consistent with the listing for some other forest-dependent São Tomé endemics. Additionally, there are other threats on the island, e.g. introduced predators (see BirdLife International 2018a), and the impacts of such threats have not been taken into account.

Therefore the species has been assessed here against all criteria.

 

Criterion A – Data from Tracewski et al. (2016) and Ł. Tracewski (unpublished data) suggests no forest loss within the species’s range between 2000 and 2012. However, as explained above, this may not mean that the species is not declining; and it may be more appropriate to make a more consistent assessment of the impacts of this threat on species, such as this, that are predominantly dependent on primary forest. Therefore, it is proposed that the species be assessed as undergoing a decline, though the rate of decline is essentially unknown and is unlikely to approach the threshold for Vulnerable.

 

Criterion B – The species has a restricted range, with an Extent of Occurrence of 360km2. The Area of Occupancy has not been calculated by IUCN guidelines (IUCN Standards and Petitions Subcommittee 2017), but it would still likely be < 500km2. Habitat loss is the main threat, but while a deforestation analysis found no forest loss within the species’s range between 2000 and 2012 (Tracewski et al. 2016, Ł. Tracewski unpublished data), there is evidence of small-scale forest clearance for agriculture occurring previously (Atkinson 1991). As of 2000 primary forest had not been affected, but road developments on the east and west coasts were opening up remote areas increasing the potential for further habitat loss (A. Gascoigne in litt. 2000). Therefore, it may be appropriate to consider there to be an ongoing decline in the area/quality of habitat and the population size at least. However, the species is not severely fragmented and it is not thought to undergo extreme fluctuations. The limited area of impact of habitat loss within the range of the species also suggests that the number of locations* where the species is found is >>10. Thus, the species would likely not warrant listing as threatened under this category; with the highest threat category it may warrant listing under being Near Threatened under criteria B1ab(iii,v)+B2ab(iii,v).

 

Criterion C – The population size is currently estimated to fall in the range 250-999 mature individuals. De Oliveira Soares (2017) observed this species at 244 point counts out of a total of 3,056, similar to other São Tomé endemics with the same current population size estimate range. Therefore, it may be appropriate to retain this range.

While some species with low population sizes on the island appear to accept modified habitats, Giant Sunbird does not appear to do so as much, with apparently only occasional records from more disturbed habitats (see BirdLife International 2018b, Cheke and Mann 2018). Therefore, as outlined above, any habitat destruction or degradation may impact the species, and to be consistent in our assessment of the impacts of threats on forest species across species the species should be assessed as declining. Therefore, the species could warrant uplisting to Endangered under criterion C2a(ii).

 

Criterion D – With a population size estimate of 250-999 mature individuals the species meets the threshold for Vulnerable under criterion D1. The species is not considered restricted enough or at few enough locations with severe enough threat 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 proposed that Giant Sunbird be listed as Endangered under criterion C2a(ii) unless there is further information or comment to show that the species should be assessed as stable. 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.

BirdLife International. 2018a. Species factsheet: Crithagra concolor. Downloaded from http://www.birdlife.org on 28/02/2018.

BirdLife International. 2018b. Species factsheet: Dreptes thomensis. Downloaded from http://www.birdlife.org on 28/02/2018.

Cheke, R.; Mann, C. 2018. Giant Sunbird (Dreptes thomensis). 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/59993 on 28 February 2018).

De Oliveira Soares, F. M. C. 2017. Modelling the distribution of São Tomé bird species: Ecological determinants and conservation prioritization. Masters Thesis, Universidade de Lisboa.

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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