Christidis, L. and Boles, W.E. 2008. Systematics and Taxonomy of Australian Birds. CSIRO Publishing, Collingwood, Australia.
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A., Fishpool, L.D.C., Boesman, P. and Kirwan, G.M. 2016. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 2: Passerines. Lynx Edicions and BirdLife International, Barcelona, Spain and Cambridge, UK.
Red List criteria met
Red List history
IUCN Red List criteria met and history
||not a migrant
Population justification: The abundance of Bower's Shrike-thrushes is calculated from the density and distribution of birds using data from standardised transect surveys along elevational gradients and the area of climatically suitable habitat at different altitudes in 2016 (Williams et al. 2010a, 2021); the population thus numbers 250,000-490,000 mature individuals, with a best estimate of 350,000.
Trend justification: A substantial decline over the past three generations is highly likely, but not all data are consistent. Annual monitoring undertaken between 2000–2016 (1,970 plots, 62 different locations, at 0–1500 m) suggests a 71.6% decline in the total population over the three generations to 2016 from an estimated 1.22 million to 350,000 mature individuals (Williams & de la Fuente 2021). The decline was most marked at mid-altitudes (450–850 m) whereas upland declines were slower and less consistent, which is congruent with climate change modelling (Williams et al. 2003).
This rate of decline is consistent with a 71% decline between 2000–2007 and 2013–2019 in the proportion of weeks in which the species was recorded (from 42%–12%) at the School for Field Studies Centre near Danbulla (740–780 m; A. Freeman, M. Craig unpublished, in Williams et al. 2021). Barnes et al. (2015), however, concluded that the prevalence of Bower's Shrike-thrush had increased on lists collected between 1996–2005, and there was no significant change in reporting rates for 2-ha 20-min surveys and 500-m radius area searches for the period of 1999–2018.
The discrepancy between analyses is thought to be because populations at lower elevations have been particularly strongly depleted, and the extent of forest and population size at those elevations is far greater than higher up the mountains where more birdwatching occurs. Williams et al. (2021) evaluated these trends and concluded that the best estimation of decline across the species’ range is 30%–49% in three generations, which is followed here.
Important Bird and Biodiversity Areas (IBA)
BirdLife International (2023) Species factsheet: Colluricincla boweri. Downloaded from
http://datazone.birdlife.org/species/factsheet/bowers-shrike-thrush-colluricincla-boweri on 30/11/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from
http://datazone.birdlife.org on 30/11/2023.