Liben lark (Heteromirafra sidamoensis)

This species is listed as Critically Endangered because it has an extremely small range, it is only confirmed to occur at a single location and its range size is decreasing. Remaining habitat is rapidly being degraded, and the number of mature individuals is decreasing (the total population is now believed to number fewer than 250 mature individuals). A potentially skewed sex ratio may mean the effective population size is even smaller, and there is a very real possibility that the species will become extinct in the next two to three years.

Heteromirafra sidamoensis was for some time known only from two specimens collected at adjacent sites near Negele in the former Sidamo province (now Guji Zone), southern Ethiopia, in May 1968 and April 1974. Since 1994 there have been subsequent sightings of small numbers (<10 on each occasion) in the Negele area. Analysis of these locations on satellite images and recent fieldwork suggests that the species is restricted to a very specific habitat (tall-grass prairie) in the calcareous plateau east and south of Negele (L. Borghesio in litt. 2005, Donald et al. 2010). Between 1973 and 2002 the area of tall-grass prairie decreased by about 30%, and in 2003 much of it was being rapidly encroached by agriculture and shrubs (Acacia drepanolobium and others) that are probably favoured by excessive grazing pressure and the suppression of seasonal fires (L. Borghesio in litt. 2005). Remaining grassland is being heavily degraded by overgrazing (Spottiswoode et al. 2009). By 2007-2008 it appeared to be restricted to a single grassland patch 30-36 km2 in area, and the global population was estimated at just 90-256 mature individuals, with the effective population size perhaps even smaller owing to a potentially skewed sex ratio caused by predation of females on the nest (Spottiswoode et al. 2009). Results of survey work to date indicate that the species has fewer than 100 territories (the number of pairs is unknown: females seem to be much scarcer than males, so many territories may be held by bachelors) (Donald et al. 2010, N. Collar in litt. 2011). 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). Predictive modelling based on the characteristics of the Liben Plain suggests that apart from a smaller and highly politically unstable area c.500 km to the north-east near the Somalian border, there is no other suitable habitat for the species within the Horn of Africa (Donald et al. 2010). The prediction of suitable habitat in eastern Ethiopia is remarkable because the area is adjacent to the type locality of Heteromirafra archeri (not seen since 1922) and is just 30 km from two fairly recent sightings of unidentified Heteromirafra larks. It is very possible that the two taxa will prove to be conspecific, but the area is likely to remain inaccessible for some time owing to extreme political instability, during which time any remaining population of Heteromirafra larks may well become extirpated (Donald et al. 2010). Thus the focus remains on the Liben Plains as the sole known location for the species (Donald et al. 2010), and without urgent and concerted intervention global extinction is likely within the next few years(Spottiswoode et al. 2009).

Liben lark
Population size:
90 – 256 individuals
Range:
< 36km2 in the Liben Plains, southern Ethiopia
Threats:
Habitat loss and degradation due
to agricultural expansion, over-
grazing and fire suppression
Action required:
Restoration of grasslands, including
establishing sustainable land
management practices, clearing
scrub and reinstating fire regime

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