Williams’s Lark (Mirafra williamsi): revise global status?

Williams’s Lark (Mirafra williamsi) is endemic to Kenya, occurring in two separate areas; north of Marsabit, and between Isiolo and Garba Tula (Keith et al. 1992). It inhabits only rocky desert areas with short grass or low shrubs (see Ryan and Sharpe 2017). Williams’s Lark was only discovered in 1955 and little is known about its ecology and life history (Lewis and Pomeroy 1989) and so it is currently assessed as Data Deficient (BirdLife International 2017).

Recent surveys in both parts of its range (Githiru et al. unpublished, Kipkoech et al. unpublished, but summarised in Magin 2013) have resulted in similar population density estimates, and so a rough population size estimate may now be possible. Encroachment and livestock grazing have tentatively been considered to be a potential threat to the species’ habitat, but it is unclear whether this is actually affecting the species and at the moment there is no evidence that they having an impact (Githiru et al. unpublished, Kipkoech et al. unpublished). As such the population trend may be considered as stable.

Therefore, given this information it may be possible to provide a clearer Red List assessment for this species.

 

Criterion A – As the population is currently considered to be stable in the absence of evidence for any declines or severe threats to the species, it does not warrant listing under this criterion.

 

Criterion B – Its Extent of Occurrence is 51,800km2 and so it does not meet the threshold for Vulnerable under criterion B1. Its Area of Occupancy has not been calculated and so it cannot be accurately assessed against criterion B2. However, it is still not thought to approach the threshold value for Vulnerable under this criterion (2,000km2).

 

Criterion C – The estimated population density for the sites covered by Kopkoech et al. (unpublished) in the northern part of its range (north of Marsabit) was 0.61 individuals per hectare; and the estimated population density for the sites covered by Githiru et al. (unpublished) in the southern part of its range (between Isiolo and Garba Tula) was 0.7±0.14 individuals per hectare. Githiru et al. did stress that their results may be not be representative for the whole area, especially as it was not found in some areas of suitable habitat. These density estimates must therefore only be used to gauge a rough population estimate rather than being used as an attempt to accurately estimate the global population size.

Based on these density estimates, and assuming only a proportion of its range is occupied gives very rough population size estimates of >200,000 mature individuals. While this could still be a large overestimate of the global population size, it is still highly unlikely that the population size is <10,000 mature individuals. Therefore, in addition to the population trend being considered to be stable, this species does not warrant listing under this criterion.

 

Criterion D – The population size is likely too large and the species not restricted to a very small area or number of ‘locations’ (see IUCN Standards and Petitions Subcommittee 2017 for IUCN definition of a ‘location’) to warrant listing under this criterion.

 

Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been carried out for this species. Therefore, it cannot be assessed against this criterion.

 

Therefore, while more ecological research is required for us to better understand this species, it appears that the species warrants listing as Least Concern. Any comments regarding this potential listing are welcome.

 

References

BirdLife International. 2017. Species factsheet: Mirafra williamsi. Downloaded from http://www.birdlife.org on 15/11/2017.

Githiru, W.; Munyekenye, F. B.; Eshiamwata, G.; Mapesa, D. H. Unpublished. Relative abundance and distribution of Williams’s Lark Mirafra williamsi in and around Shaba National Reserve, Kenya.

IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Keith, S.; Urban, E. K.; Fry, C. H. 1992. The birds of Africa vol. IV. Academic Press, London.

Kipkoech, S.; Nderitu, W.; Thaniriwa, P. Unpublished. Population survey and environmental threat assessment of Williams’s Lark, Mirafra williamsi, in Dida Galgalu Desert IBA.

Lewis, A.; Pomeroy, D. 1989. A bird atlas of Kenya. A. A. Balkema, Rotterdam.

Magin, C. 2013. African Bird Club conservation fund. Bull. Afr. Bird Club 20: 8.

Ryan, P.; Sharpe, C. J. 2017. Williams’s Lark (Mirafra williamsi). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/57598 on 15 November 2017).

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