Archived 2010-2011 topics: São Tomé Thrush (Turdus olivaceofuscus): list as Near Threatened?

Link to BirdLife factsheet for São Tomé Thrush (pre-split)

São Tomé Thrush Turdus olivaceofuscus has been split into T. olivaceofuscus and T. xanthorhynchus following Melo et al. (2010). Prior to this taxonomic change, T. olivaceofuscus was listed as Near Threatened under criteria C1; D1, on the basis that although the population was estimated to number 1,000-2,499 individuals, there was no evidence of a decline in the overall population.

Following this taxonomic change, Dallimer et al. (2010) recommend that T. olivaceofuscus be listed as Least Concern based on observed densities in primary forest and because the species is considered to be common across the entire island in most habitats. However, the species’s Extent of Occurrence is estimated at only 860 km2, with its population surely numbering fewer than 2,500 individuals. It is still potentially threatened by the destruction and degradation of optimal habitats, as well as the continued degradation of already modified habitats. In particular, there is concern over the removal of shade trees from cocoa plantations, as well as the compounding effects of land privatisation and road building (del Hoyo et al., 2005). In addition, many nests are destroyed by brown rats Rattus norvegicus (del Hoyo et al. 2005). Although there is no evidence of a decline in the population, there are ongoing threats that could be impacting the species.

For all of these reasons it is proposed that the species be listed as Near Threatened under criteria B1a+b(iii,v); C1; D1. Comments are invited on this proposed listing as well as further information on the species.

Dallimer, M., Melo, M., Collar, N. J. and Jones, P. J. (2010) The Príncipe Thrush Turdus xanthorhynchus: a newly split, ‘Critically Endangered’, forest flagship species. Bird Conserv. Int. Published online 27 July 2010. Accessed 21/10/2010: http://journals.cambridge.org/download.php?file=%2FBCI%2FS0959270910000390a.pdf&code=9c9cc1f4e3b45c06d298f403f4d38dc7

del Hoyo, J., Elliott, A. and Christie, D. (2005) Handbook of the Birds of the World, vol. 10: Cuckoo-shrikes to Thrushes. Barcelona, Spain: Lynx Edicions.

Melo, M., Bowie, R. C. K., Voelker, G., Dallimer, M., Collar, N. J. and Jones, P. J.
(2010) Multiple lines of evidence support the recognition of a very rare bird species –
the Príncipe thrush. J. Zool. doi: 10.1111/j.1469.7998.2010.00720.x.

Following his post on 9 December 2010, Ricardo Faustino de Lima has submitted the following figures (not BirdLife data):

Fig 1. Frequency of the endemic birds of Sao Tome across land-uses. Column height represents the number of counts in which the species was present at less than 20m from the sampling location.

Fig 2. Distribution of selected endemic bird species of Sao Tome. Each sampling location is marked by a small dot. The frequency of each species (number of counts in which the species was present at less than 20m from the sampling location) is represented by the size of a shape representing land-use type: circle - old growth forest; square - secondary forest; triangle - shade plantation; losange - other agricultural land-use.

Related posts:

  1. Archived 2010-2011 topics: Principe Thrush (Turdus xanthorhynchus): newly split and Critically Endangered?
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2 Responses to Archived 2010-2011 topics: São Tomé Thrush (Turdus olivaceofuscus): list as Near Threatened?

  1. I am currently doing my Phd about Sao Tome’s avifauna and as such I have recently conducted point counts in Sao Tome, to survey bird communities across the island’s different land-uses.

    According to preliminary analyses of my data, the Sao Tome Thrush (Turdus olivaceofuscus) is one of the most frequent endemic bird species, but it seems to be slightly more sensitive to land-use intensification than other frequent endemics. A possible explanation for this sensitivity might be hunting pressure, as the species is commonly collected by kids with slingshots (a major occupation in rural communities, especially during the hollidays).

    Given the abundance of the species throughout most of the island’s land-uses and the strong hunting pressure to which is subjected, I argue that its population must be larger than 2,500 individuals. As for all species endemic to this island, its Extent of Occurrence is surely smaller than 860 km² and therefore it should become threatened if there is a continue decline due to a pervasive threat (as a pervasive threat would mean that the species is restricted to a single location, according to the guidelines’ definition of location).

    Sao Tome’s habitats are currently under threat. Human population is growing very fast (2% effective growth rate per year) and there is growing foreign investement on the island, namely for agricultural projects (expand an oil palm monoculture up to 3500ha plus support 1500ha of small oil palm producers, several investments in fair trade and organic coffee and cocoa, and more recently prospects to export horticultural goods to Cape Verde and Libia). Little is known about the extent of the impact of these changes across the island (especially when it comes to indirect impacts such as increased accessibility, urbanisation and displacement of small farmers), but habitat destruction and degradation of habitats (better or worst preserved) should no longer be considered a mere potential threat, but rather an ongoing and increasing threat.

    For all of these reasons I believe that the thrush might become threatened in a nearby future and agree with listing this species as Near Threatened, until the current trends of ongoing threats are better evaluated. Nonetheless I only agree with criteria B1a+b(iii,v) and C1.

    Furthermore, I would suggest that other Sao Tome endemisms should also be moved to the Near Threatened category, under this same criteria. The Sao Tome paradise flycatcher (Terpsiphone atrochalybeia), the Sao Tome green pigeon (Treron sanctithomae) and the giant weaver (Ploceus grandis), which according to my data are all less frequent than the thrush and at least as sensitive to land-use changes. Additionally, the Sao Tome spine-tail (Zoonavena thomensis) and the Gulf of Guinea bronze-naped pigeon (Columba malherbii) could also be moved to the Near Threatened category since they are much less frequent than the thrush, despite not being single island endemisms (occuring in neighbouring smaller islands) or as sensitive to land-use changes.

  2. Continuing on the last paragraph from the previous post and supported by the graphics that are now available at the top, I argue that there seems to be inconsistencies between the current threat status of the highlighted endemic species (Fig. 2) and the frequencies I’ve measured across land-uses (Fig. 1). Therefore, if the threat status of the thrush (Turdus olivaceofuscus), oriole (Oriolus crassirostris) and white-eye (Zosterops ficedulinus) are not to be changed (as I agree they shouldn’t), there is justification to change the classification of the:
    - Sao Tome paradise flycatcher (Terpsiphone atrochalybeia) from LC to NT, since the frequencies and habitat sensitivities are identical to those of the thrush. Furthermore there is a record of this species’ sensitivity to the use of pesticides (Jones & Tye 1988, which classified the species as NT at the time), which should be a further reason of concern for this species in the current trends of agriculture intensification. The criteria would be the same as for the thrush.
    - Giant weaver (Ploceus grandis) also from LC to NT, since this species is the least frequent of the highlighted in Fig. 2 (Fig. 1). Again, the criteria would be the same as for the thrush.
    - Sao Tome green pigeon (Treron sanctithomae) from LC to VU, since this species is quite habitat sensitive and less frequent than either the thrush, the paradise flycatcher, the oriole or the white-eye (Figs. 1 & 2). Furthermore this species is also a favoured quarry species (to be further discussed in the “Sao Tome’s pigeons” topic).
    As I said previously, the Sao Tome spine-tail (Zoonavena thomensis) and the Gulf of Guinea bronze-naped pigeon (Columba malherbii) could also be moved from LC, pending on data from the remaining extent of occurrence (Principe and Annobon).

    Jones, P. & Tye, A. (1988). A survey of the avifauna of São Tomé & Príncipe. ICBP Study Report 24. ICBP, Cambridge, UK.

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