Birdlife International factsheet for Dusky Long-tailed Cuckoo.
Following a taxonomic reassessment, Dusky Long-tailed Cuckoo (Cercococcyx mechowi) has been split into Dusky Long-tailed Cuckoo (C. mechowi), and Whistling Long-tailed Cuckoo (C. lemaireae) (see Boesman and Collar, 2019). The newly-split Dusky Long-tailed Cuckoo has a range extending from central Cameroon east to Uganda. Whistling Long-tailed Cuckoo ranges from Sierra Leone to western Cameroon (Boesman and Collar, 2019).
The exact habitat requirements for the newly-split Whistling Long-tailed Cuckoo have not been investigated, but it is very likely to require lowland and montane forests, and have the same high forest dependency as Dusky Long-tailed Cuckoo (del Hoyo et al., 2002). This high forest dependency may render these species vulnerable to forest loss. The population size of the pre-split species is unknown, but it is described as relatively uncommon but not rare (del Hoyo et al., 2002).
The pre-split species was previously listed as Least Concern (BirdLife International 2020). However, following the taxonomic split, new range sizes suggest that both species warrant a thorough reassessment. We have therefore reassessed both species against each criterion here.
IUCN guidelines stipulate that rates of decline should be measured over the longer of 10 years or 3 generations (IUCN Standards and Petitions Committee, 2019). The generation length for Dusky Long-tailed Cuckoo has been recalculated to 4.3 years (Bird et al., 2020)*. Therefore, the rates of reduction for these species are calculated over 12.3 years.
Dusky Long-tailed Cuckoo: The population trend for this species has not been directly estimated, but it is suspected to be declining as a result of ongoing habitat loss (Tracewski et al., 2016; Birdlife International, 2020). Between 2000-2018, this species’s range lost 16% of its tree cover (Global Forest Watch, 2020). Assuming that population size declines at the same rate as habitat loss, this equates to a population size reduction of 11.3% in three generations. Tracewski et al. (2016) also found insignificant deforestation rates in their analysis. A three-generation decline rate of 11.3% does not meet the threatened threshold (≥ 30% population size reduction) under this criterion. Dusky Long-tailed Cuckoo may therefore be considered Least Concern under criterion A.
Whistling Long-tailed Cuckoo: This newly-split species may also be at risk from habitat loss. Between 2000-2018, 14% of tree cover was lost across this newly-split species’s range. Assuming population size declines at the same rate as habitat loss, this equates to a population size reduction of 9.8% in three generations. Tracewski et al. (2016) also found insignificant deforestation rates in their analysis. A three-generation decline rate of 9.8% does not meet the threatened threshold under this criterion. Whistling Long-tailed Cuckoo may therefore be considered Least Concern under criterion A.
Dusky Long-tailed Cuckoo: The Extent of Occurrence (EOO) for this species is calculated as 3,280,000 km². This is too large to trigger the threatened threshold under this criterion (EOO <20,000 km²). Dusky Long-tailed Cuckoo may therefore be considered Least Concern under criterion B.
Whistling Long-tailed Cuckoo: The EOO for this species is calculated as 1,450,000 km². This is too large to trigger the threatened threshold under this criterion (EOO <20,000 km²). Whistling Long-tailed Cuckoo may therefore be considered Least Concern under criterion B.
The population sizes for these species have not been estimated. Other cuckoo species have been observed in population densities of between 0.06-0.6 birds/ha (see Martins et al., 2018; Ringim et al., 2018). Even assuming that C. mechowi and C. lemaireae are found at the lower density estimates, and that only 10% of their large ranges are occupied, the populations of both species would be far greater than the threshold of <10,000 mature individuals needed to qualify as threatened under this criterion. As such, both species may be considered Least Concern under criterion C.
The population sizes for these species, based range sizes and the density estimates of other cuckoo species, are likely to be far higher than the threshold of 1000 mature individuals needed to qualify as threatened here. Both C. mechowi and C. lemaireae may be considered Least Concern under criterion D.
Criterion E: To the best of our knowledge, no quantitative analysis has been carried out for these species. We therefore cannot assess either of them against criterion E.
We therefore suggest that both Dusky Long-tailed Cuckoo (C. mechowi) and Whistling Long-tailed Cuckoo (C. lemaireae) be listed as Least Concern. We welcome any comments to the proposed listing.
Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’s Red List status. Therefore, please make sure your comments are relevant to the species’ Red List status and the information requested. 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., Şekercioğlu, Ç.H. and 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 (2020) Species factsheet: Cercococcyx mechowi. Downloaded rom http://www.birdlife.org on 14/05/2020
Boesman, P., and Collar, N.J., (2019), Two undescribed species of birds from West Africa, Bulletin of the British Ornithologists’ Club, 139(2) : 147-159
del Hoyo, J.; Elliott, A.; Sargatal, J. 2002. Handbook of the Birds of the World, vol. 7: Jacamars to Woodpeckers. Lynx Edicions, Barcelona, Spain.
Global Forest Watch. 2020. World Resources Institute. http://www.globalforestwatch.org (Accessed 14 May 2020).
IUCN Standards and Petitions Committee. 2019. Guidelines for using the IUCN Red List Categoreis and Criteria. Version 14. http://www.iucnredlist.org/documents/RedListGuidelines.pdf
Martins, C.O., Zakaria, M., Olaniyi, O.E., and Angela, U.O., 2018, Population Density of Avian Species in a Man-Made Wetland of Peninsular Malaysia, International Conference on Biodiversity, IOP Conf. Series: Earth and Environmental Science 269
Ringim, A.S., Magige, F.J., and John, J.R.M., 2018, Diversity and density of avifauna in areas with different protection status: A case study in Hadejia-Nguru Wetlands, North-eastern Nigeria, International Journal of Ecology and Environmental Sciences 44 (2), pp: 117-125
Tracewski, Ł.; Butchart, S. H. M.; Di Marco, M.; Ficetola, G. F.; Rondinini, C.; Symes, A.; Wheatley, H.; Beresford, A. E.; 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.