VU
Bower's Shrike-thrush Colluricincla boweri



Taxonomy

Taxonomic source(s)
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.

IUCN Red list criteria met and history
Red List criteria met
Critically Endangered Endangered Vulnerable
- - A2bc+3c+4bc

Red List history
Year Category Criteria
2022 Vulnerable A2bc+3c+4bc
2016 Least Concern
2012 Least Concern
2009 Least Concern
2008 Least Concern
2004 Least Concern
2000 Lower Risk/Least Concern
1994 Lower Risk/Near Threatened
1988 Lower Risk/Least Concern
Species attributes

Migratory status not a migrant Forest dependency Medium
Land mass type Average mass 44 g
Distribution

Estimate Data quality
Extent of Occurrence breeding/resident (km2) 17,600
Number of locations -
Severely Fragmented -
Population and trend
Value Data quality Derivation Year of estimate
No. of mature individuals 250000-490000, 350000 medium estimated 2020
Population trend Decreasing estimated -
Decline (3 years/1 generation past) - - -
Decline (5 years/1 generation past) - - -
Decline (10 years/1 generation past) - - -
Decline (10 years/3 generation future) 30-49 - - -
Decline (10 years/3 generation past and future) 30-49 - - -
Number of subpopulations 1 - - -
Percentage in largest subpopulation 100 - - -
Generation length (yrs) 4 - - -

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.


Country/territory distribution
Country/Territory Occurrence status Presence Resident Breeding Non-breeding Passage
Australia N Extant Yes

Important Bird and Biodiversity Areas (IBA)
Country/Territory IBA Name
Australia Daintree
Australia Paluma
Australia Wooroonooran
Australia Coastal Wet Tropics

Habitats & altitude
Habitat (level 1) Habitat (level 2) Importance Occurrence
Artificial/Terrestrial Subtropical/Tropical Heavily Degraded Former Forest suitable resident
Forest Subtropical/Tropical Moist Lowland suitable resident
Forest Subtropical/Tropical Moist Montane major resident
Shrubland Subtropical/Tropical High Altitude suitable resident
Shrubland Subtropical/Tropical Moist suitable resident
Altitude 400 - 2230 m Occasional altitudinal limits  

Threats & impact
Threat (level 1) Threat (level 2) Impact and Stresses
Climate change & severe weather Habitat shifting & alteration Timing Scope Severity Impact
Ongoing Whole (>90%) Rapid Declines High Impact: 8
Stresses
Ecosystem degradation
Climate change & severe weather Temperature extremes Timing Scope Severity Impact
Ongoing Whole (>90%) Rapid Declines High Impact: 8
Stresses
Species mortality

Recommended citation
BirdLife International (2022) Species factsheet: Colluricincla boweri. Downloaded from http://www.birdlife.org on 02/10/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 02/10/2022.