Archived 2010-2011 topics: Principe Thrush (Turdus xanthorhynchus): newly split and Critically Endangered?

Link to BirdLife factsheet for Sao Tome Thrush (pre-split)

Principe Thrush Turdus xanthorhynchus has been split from Sao Tome Thrush T. olivaceofuscus 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 for a decline in the overall population.

This taxonomic change has prompted a re-evaluation of the Red List status of both taxa, which is aided by a recent study into their status (Dallimer et al. 2010). During a survey of Principe in 2007 covering 177 point transect locations at 13 sites in primary forest, secondary forest and plantations, only 18 individuals of T. xanthorhynchus were recorded, the majority above 400 m, with the highest density above 600 m (Dallimer et al. 2010). From this survey data a total population estimate of 364 birds (95% CI: 186-887) was calculated. This estimate incorporates the observed variation in abundance with elevation, which if ignored results in an estimate of 435 individuals (95% CI: 208-913). These are both considered to be overestimates by Dallimer et al. (2010) on the basis that the species does not occupy all areas of primary forest and the possibility that surveyed numbers were biased high because the species readily approaches humans. With this in mind, along with the likelihood that a relatively high proportion of the birds encountered were probably non-breeders, Dallimer et al. (2010) estimate the population of mature individuals to number fewer than 250.

The species may also be in decline. Dallimer et al. (2010) assert that people who use the forest on Principe must readily kill T. xanthorhynchus if they have the opportunity, as it is very tame. However, they do not provide any data or anecdotal evidence to support this apparent speculation. Nevertheless, comparison with past surveys and information from local people suggest that the species is disappearing from areas of forest frequently used by people. There is certainly evidence that past deforestation since human colonisation in the 1500s (Jones and Tye 2006) would have led to dramatic declines in this species. Deforestation is still a potential threat, although much reduced by the recent designation of Parque Natural d’Obô do Príncipe, which covers most of the remaining primary forest (Dallimer et al. 2010).

On the basis of their recent findings, Dallimer et al. (2010) recommend that T. xanthorhynchus be listed as Critically Endangered under criteria B1a+b(iii,v); C2a(ii), on the basis that the species has a population estimated at fewer than 250 mature individuals, of which at least 90% are in one sub-population, occupying an Extent of Occurrence estimated at less than 100 km2, in which it is found at one location, and is suspected to be declining owing to the threats of persecution and deforestation. This recommended listing is judged to adhere to the IUCN criteria and is therefore proposed for the species. Comments are invited on this proposal, as well as any additional 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

Jones, P. and Tye, A. (2006) The birds of São Tomé and Príncipe, with Annobón: islands of the Gulf of Guinea. BOU Checklist No 22. Oxford: British Ornithologists’ Union/British Ornithologists’ Club.

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.

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