Archer’s Lark (Heteromirafra archeri) and Liben Lark (H. sidamoensis) are being lumped as Liben Lark (H. archeri) following new analysis of morphological, molecular and vocal evidence (Spottiswoode et al. 2013).
Prior to this taxonomic change, both H. archeri (BirdLife species factsheet) and H. sidamoensis (BirdLife species factsheet) were listed as Critically Endangered under Critieria B1 and C2 as a result of their extremely small ranges and small, declining populations.
H. archeri was known only from a very restricted area from Jifa Medir to Ban Wujaleh, west of Hargeisa in northwest Somalia and had not been recorded with certainty since 1955 (J.G. Williams in litt 1984). It was therefore thought to have an extremely small range and was considered likely to be declining as a result of habitat loss and degradation. Its population was estimated at 50-249 mature individuals.
H. sidamoensis was thought to be restricted to the grassland of the Liben Plain in southern Ethiopia and by 2007-2008 appeared to be restricted to an area of 30-36 km2 (Spottiswoode et al. 2009). The adult male population was estimated at 63-179, with the total number of mature individuals estimated at 90-256, taking into account a potential sex-ratio bias caused by predation of females on the nest (Spottiswoode et al. 2009). The amount and quality of habitat at the Liben Plain have declined as a result of overgrazing, conversion to agriculture and overgrazing (Collar et al. 2008; Donald et al. 2010).
In the last decade, individuals of a Heteromirafra species were recorded east of Jijiga in northeast Ethiopia (Spottiswoode et al. 2013), ca. 50km from where H. archeri had previously been recorded . Analysis of morphological and molecular evidence has now shown that this newly discovered population is conspecific with H. archeri, and analysis of morphological, molecular and vocal evidence showed that both of these populations are conspecific with H. sidamoensis. The newly defined species has retained the common name Liben Lark and the scientific name H. archeri (Spottiswoode et al. 2013).
The type locality of H. archeri in Somalia is now known to have been completely transformed through agriculture, grazing and invasion of the alien plant species Parthenium hysterophorus and this population has probably been lost (Spottiswoode et al. 2013). The newly-defined species is therefore likely to be restricted to two small areas 590km apart: an area east of Jijiga in northeast Ethiopia and the Liben Plain in southern Ethiopia.
H. archeri prefers grassland habitat with a greater than average grass cover (Donald et al. 2010; Spottiswoode et al. 2013). Environmental niche models suggest that the species is restricted to tall prairie grass and that apart from a few small, scattered sites in central Ethiopia that are thought unlikely to support populations of H. archeri, there are no other areas of suitable habitat within the region (Donald et al. 2010).Niche modelling predicted a total of 580 1km2 cells with habitat suitable for the species (Spottiswoode et al. 2013).
The grassland of the Liben Plain has continued to be lost and degraded and it is likely that this population of H. archeri continues to decline. Compared with a survey in June 2007, fieldwork in May 2009 recorded a decline of 40% in the number of birds present along repeated transects and a contraction of 38% in the area of the Liben Plain occupied by the species (Donald et al. 2010). Surveys in 2011 showed a further decrease in occupied area and a 44% reduction on that recorded in 2007 (Abdu 2012). Over 15% of remaining habitat on the Liben Plain was lost in a single year (P. F. Donald in litt. 2012).
The H. archeri population near Jijigi is restricted to a small area of heavily degraded grassland with a maximum estimated extent of 20km x 12km (Spottiswoode et al. 2013). The grass is heavily grazed and many areas have recently been cultivated (Spottiswoode et al. 2013). Surveys have shown that this area has a higher proportion cover of very short grass (<5cm) than the Liben Plain. The H. archeri population near Jijiga is therefore also likely to be small and in steep decline (Spottiswoode et al. 2013).
Given the small size and rapid ongoing decline of the population on the Liben Plain, it is likely that this population is now extremely small and considerably lower than the 2007 estimate of 90-256 mature individuals. If the range of this population continues to contract at the same rate as seen over recent years, the population could be lost completely within 1-2 generation lengths. Given that surveys in 2007 and 2009 showed a decline of 40% in the number of birds present along repeated transects and a contraction of 38% in the area occupied by the species, across just two years, the Liben Plain population may be predicted to undergo a reduction of over 80% within three generation (11.4 years).
Less is known about the population near Jijiga, but the area of available habitat is small and is probably unlikely to hold a population greater than that of the Liben Plain. The habitat here is similarly degraded to that at the Liben Plain (with an even higher proportion of coverage of short grass) and cultivation of the grassland has been seen to be ongoing (Spottiswoode et al. 2013), so a similar ongoing steep decline can be assumed to be underway in this population.
Based on the available evidence, it can therefore be concluded that the total population of H. archeri can be projected to undergo a reduction of greater than 80% over the period of three generations and greater than 25% in one generation. The total population is now likely to number fewer than 250 individuals, with fewer than 50 individuals in each of the two subpopulations. It is therefore proposed that the newly defined species H. archeri is listed as Critically Endangered under criteria A3+4; C1+2.
Additional information and comments on this proposal are welcomed.
Abdu, B. 2012. Abundance, habitat association and behavioral pattern of the Liben lark (Heteromirafra sidamoensis), Liben District, Guji Zone, Southern Ethiopia. Unpublished master’s thesis, Addis Ababa University, Ethiopia.
Collar, N.J., Abebe, Y.D., Fishpool, L.D.C., Gabremichael, M.N., Spottiswoode, C.N., Wondafrash, M. 2008. Type locality, habitat, behaviour, voice, nest, eggs and plight of the Sidamo Lark Heteromirafra sidamoensis. Bulletin of the African Bird Club 15(2): 180-190.
Donald, P.F., Buchanan, G.M., Collar, N.J., Abebe, Y.D., Gabremichael, M.N., Mwangi, M.A.K., Ndang’ang’a, P.K., Spottiswoode, C.N. & Wondafrash, M. 2010. Rapid declines in habitat quality and population size of the Liben (Sidamo) Lark Heteromirafra sidamoensis necessitate immediate conservation action. Bird Conservation International 20(1): 1-12.
Spottiswoode, C.N., Olsson, U., Mills, M.S., Cohen, C., Francis, J.E., Toye, N., Hoddinott, D., Dagne, A., Wood, C., Donald, P.F., Collar, N.J. & Alström, P. 2013. Rediscovery of a long-lost lark reveals the conspecificity of endangered Heteromirafra populations in the Horn of Africa. Journal of Ornithology 154(3): 813-825.
Spottiswoode, C.N., Wondafrash, M., Gabremichael, M.N., Abebe, Y.D., Mwangi, M.A.K., Collar, N.J. & Dolman, P.M. 2009. Rangeland degradation is poised to cause Africa’s first recorded avian extinction. Animal Conservation 12(3): 249-257.