BirdLife species factsheet for Chestnut-capped Thrush
The Chestnut-capped Thrush is a songbird species resident throughout the Sundaland region of Southeast Asia; including both Peninsular and Borneo’s East Malaysia, Brunei, and across Indonesia (including parts of Sumatra, Java, Kalimantan and the Lesser Sunda islands) (Collar, 2020). The species also occurs on the southernmost range of peninsular Thailand and may be a rare resident in the Philippines (including the Sulu and Basilan Islands). The species prefers lowland habitats, including primary, tall secondary and logged forests, woodlands, and woodlots (Collar, 2020). The species is rare and local throughout most of its range, considered ‘fairly common’ only in Borneo and the Lesser Sundas. The species is a recent coloniser in Krakatau (Collar, 2020).
The species was previously considered to be undergoing a moderately rapid decline due to forest loss and trapping for the cage bird trade. A recent forest analysis of the Sundaland region suggests that the Chestnut-capped Thrush may be continuing to face high risk from surrounding habitat loss (Symes et al. 2018). Owed to a number of factors such as logging, land conversion for industrial plantations, and forest fires, the Sundaic lowlands had experienced a loss of over 70% of its original forest cover by 2010 alone (Symes et al., 2018). The species is also thought to fare poorly in logged forests, occurring in low densities in these habitats (D. Edwards in litt., 2020). The intensive trade for birds further compounds forest destruction and habitat loss, with the Chestnut-capped Thrush facing significant pressures in trapping for domestic and international markets (Symes et al., 2018).
The population size of the species was previously unknown. Applying appropriate conversions to population densities based on territories and singing birds however suggest that the species may number 2.75-100 pairs/km2 (Collar, 2020); converted here to 5.5-200 mature individuals/km2. The maximum of this estimate is however based on locally very high densities of the species and may therefore overestimate its presence (Collar, 2020). Thus, to account for the apparent rarity of the species in parts of its range, the lower estimate (c. 5.5 mature individuals/km2) is used therein. Precautionarily assuming that 10% of the total mapped range (c. 674,550 km2) is occupied, the population may therefore number 371,002 mature individuals. To account for uncertainty, the population is placed tentatively in the band of 100,000-499,999 mature individuals.
The Chestnut-capped Thrush is currently listed as Near Threatened, based on a moderately rapid decline rate that approaches a threatened status, resulting from forest loss and trapping for the cage bird trade. However, information regarding hunting and forest loss data may warrant a change in Red List status. Therefore, the species will be re-assessed against all criteria:
Criterion A – The Chestnut-capped Thrush is thought to be undergoing population declines due to habitat loss and trapping and hunting for trade. A recent study investigating both factors across the Sundaic region found that forest loss and hunting pressures had caused an estimated 67.5% decline over 10 years (Symes et al., 2018; see also Tracewski et al., 2016). Following recent findings, the generation length of the Chestnut-capped Thrush is thought to be 4.5 years (Bird et al., 2020)*. The relevant timeframe for an assessment against Criterion A is three generation lengths, which is equivalent to 13.5 years for this species. A population decline of 67.5% over 10 years equates to 78.1% decline over 13.5 years. The species therefore initially qualifies for an Endangered status under Criterion A.
However, it is important to consider that these population decline estimates covered only the Greater Sundaic range, and did not include the Lesser Sunda Islands where the species is regarded to be trapped intensely (F. Rheindt in litt. 2020). Its presence in the Lesser Sunda Islands is therefore becoming increasingly rare, albeit has not been formerly quantified. Given the overall large spread of the species throughout much of the Sundaic region however, and to account for any uncertainty in population declines therefore, it is suspected that declines are in any case ≥30% (F. Rheindt in litt. 2020); placed tentatively in the band of 30-49% decline. We can also assume that population declines are likely to continue into the future. Thus, the species may qualify for a Vulnerable listing under Criterion A2cd+A3cd+A4cd. We however welcome any recent information regarding population trends that cover the entirety of the species range.
Criterion B – The Extent of Occurrence (EOO) for this species is estimated at 4,270,000 km2. This is outside the required threshold for a threatened status under Criterion B1, and the species qualifies for Least Concern under Criterion B1. The Area of Occupancy (AOO) was not quantified for this species as required (see IUCN Standards and Petitions Committee, 2019); thus, the species cannot be assessed against Criterion B2.
Criterion C – The estimated population size of this species (100,000-499,999 mature individuals) is outside the required thresholds for a threatened status under this criterion. Therefore, the species qualifies for Least Concern under Criterion C.
Criterion D – The estimate population size and range of this species does not approach any relevant threshold for a threatened status under this criterion. Therefore, the species qualifies for Least Concern under Criterion D.
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 suggested that the Chestnut-capped Thrush (Geokichla interpres) be reclassified as Vulnerable A2cd+3cd+4cd. We therefore welcome any comments on the above proposed listing and specifically ask for any recent population trends. We additionally ask for information on the timeframe of declines: Data from Symes et al. (2018) suggests that declines accelerated between 2000 and 2015, meaning that the species may have crossed the threshold for listing as Vulnerable during 2008-2012 or during 2012-2016. We welcome any comments to the proposed listing and suggested timing of change.
Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic. By submitting a comment, you confirm that you agree to the Comment Policy.
*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).
An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.
Bird, J. P.; Martin, R.; Akçakaya, H. R.; Gilroy, J.; Burfield, I. J.; Garnett, S.; Symes, A.; Taylor, J.; Šekercioğlu, Ç.; Butchart, S. H. M. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.
BirdLife International (2016). Geokichla interpres. The IUCN Red List of Threatened Species 2016.
Collar, N. (2020). Chestnut-capped Thrush (Geokichla interpres), version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana; Editors). Cornell Lab or Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.chcthr1.01
D. Edwards (2020). Asian Songbird Trade Specialist Group. In litt.
F. Rheindt (2020). Asian Songbird Trade Specialist Group. In litt.
IUCN Standards and Petitions Committee. 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf
Symes, W. S., Edwards, D. P., Miettinen, J., Rheindt, F. E., and Carrasco, L. R. (2018). Combined impacts of deforestation and wildlife trade on tropical biodiversity are severely underestimated. Nature Communications 9: 4052.
Tracewski, Ł., Butchart, S. H. M., Di Marco, M., Ficetola, G. F., Rondinini, C., Symes, A., Wheatley, H., Beresford, A. E., and 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.