Archived 2020 topic: Dusky Long-tailed Cuckoo (Cercococcyx mechowi) is being split: assessment of newly recognised taxa.

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.

Criterion A:

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.

Criterion B:

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.

Criterion C:

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.

Criterion D:

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.

References

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.

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5 Responses to Archived 2020 topic: Dusky Long-tailed Cuckoo (Cercococcyx mechowi) is being split: assessment of newly recognised taxa.

  1. Red List Team (BirdLife International) says:

    Global Forest Change data on tree cover loss up to 2019 have now been released and made available via Global Forest Watch. Based on these data, over 12.3 years approximately 18.4% of tree cover with 75% canopy cover was lost from within the range of the Dusky Long-tailed Cuckoo, and approximately 6% of tree cover with 75% canopy cover was lost from within the range of the Whistling Long-tailed Cuckoo (Global Forest Watch 2020). This does not affect the above assessment under Criterion A.

  2. Ben Phalan says:

    Based on the limited information available, it seems quite likely that Whistling Long-tailed Cuckoo qualifies as threatened.

    In Ghana, it is restricted to a very few sites within the wetter, western part of the forest zone, and many records from elsewhere in the country (e.g. Kakum, Ankasa) are likely misidentifications of the common Olive Long-tailed Cuckoo. The most important sites are Ankasa and Tano Ofin. This is not shown well on the BirdLife distribution map, which does not extend south to Ankasa. I hope this can be corrected when the split is implemented (using, for example, the modified map from Boesman & Collar 2019).

    Dowsett-Lemaire & Dowsett (2014) in their Ghana Atlas considered that the species may have been extirpated from Bia National Park. A study from Ghana by Arcilla et al. had a capture rate of 0.11 Whistling Long-tailed Cuckoos per 10,000 net-metre-hours in 1993-1995, and this fell to 0.00 (zero) in 2008-2010, following a period when logging activity increased by >600%. This finding should be taken as indicative only, as many of the sites in this study never held the species and were likely unsuitable. However, it is suggestive that the species could be sensitive to forest degradation, not just forest loss, and therefore its rate of decline could be worse than that suggested by the Global Forest Watch analysis.

    Other information suggestive of a decline is that Colston & Curry-Lindahl (1986) considered this species “fairly common” in the late 1960s/early 1970s at Mt. Nimba, Liberia. Gatter (1997) corroborated this assessment based on fieldwork in the 1980s. Fieldwork by multiple experienced observers (including Ron Demey, and Françoise Dowsett-Lemaire, after whom this new species is named) in 2008, 2009, 2010 and 2011 resulted in only a single record of the species from the Mt. Nimba area, although there is an abundance of apparently suitable habitat. Dowsett-Lemaire & Phalan (2013) concluded that “[e]ither this species has decreased, or it is a very seasonal caller, or its calls were confused with those of another cuckoo.” [by Alec Forbes-Watson, whose work informed the book by Colston & Curry-Lindahl]

    I may have misunderstood, but there seems to be a small error in the calculation of three generation lengths: 4.3 times 3 is 12.9 years, not 12.3.

    In conclusion, this newly-recognised species is likely to be sensitive to forest degradation; legal and illegal logging are extensive throughout its range and their impacts are not well captured by Global Forest Watch data; there is some evidence the species has declined or disappeared from formerly occupied sites; and thus its rate of decline could well be much higher than that of forest cover. My suggestion would be either to list it as Near Threatened pending better evidence, or precautionarily list it as Vulnerable with a suspected decline of >30% over three generations as a result of the combined impact of forest loss and degradation.

    Arcilla, N., Holbech, L. H., & O’Donnell, S. (2015) Severe declines of understory birds follow illegal logging in Upper Guinea forests of Ghana, West Africa. Biological Conservation, 188, 41–49.

    Boesman, P., & Collar, N. J. (2019) Two undescribed species of bird from West Africa. Bulletin of the British Ornithologists’ Club, 139(2), 147–159.

    Colston, P. R., & Curry-Lindahl, K. (1986) The Birds of Mount Nimba, Liberia. British Museum (Natural History).

    Dowsett-Lemaire, F., & Dowsett, R. J. (2014) The Birds of Ghana: An Atlas and Handbook. Tauraco Press.

    Dowsett-Lemaire, F., & Phalan, B. (2013) Nimba Western Area Iron Ore Concentrator Mining Project, Liberia. Environmental and Social Impact Assessment Volume 4, Part 2, Appendix 2: Ornithological Surveys in the Nimba Mountains in October-November 2011, with special reference to East Nimba Nature Reserve and the West Nimba (Gba) Community-Managed Forest. Report to URS for ArcelorMittal.

    Gatter, W. (1997) Birds of Liberia. Yale University Press.

  3. Red List Team (BirdLife International) says:

    Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested by so many people in commenting. The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.

    Thank you once again,
    BirdLife Red List Team

  4. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2020 Red List would be to list

    Dusky Long-tailed Cuckoo as Least Concern, and

    Whistling Long-tailed Cuckoo as Near Threatened under Criterion A2abc+3c+4abc.

    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.

    The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN. The final publication date will be publicised by IUCN here: https://www.iucnredlist.org/assessment/updates

  5. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    The final categorisations for these species have not changed.
    Dusky Long-tailed Cuckoo is recommended to be listed as Least Concern.
    Whistling Long-tailed Cuckoo is recommended to be listed as Near Threatened, approaching a listing as threatened under Criterion A2abc+3c+4abc.

    Many thanks for everyone who contributed to the 2020 GTB Forum process. The final 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020/January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.