Climate and the restricted range of the Ethiopian Bush-crow

Distribution of the 4,455 1-km cells predicted to contain suitable land cover (dark blue) within 

the envelope of 6.001 1-km cells with optimal climate suitalility (light and dark blue) in southern Ethiopia. 

In a study, published in 2012 in the Journal of Ornithology*, we attempt to describe and explain the peculiarly restricted distribution of the globally threatened Ethiopian Bush-crow Zavattariornis stresemanni. At a regional scale, models containing only correlates of land cover suggested a far wider distribution of suitable habitat in north-east Africa than the area actually occupied. However, models including only climate variables predicted the known distribution almost perfectly, and suggested that the species’ area of occupancy is delimited by a pocket of climate that is cooler, dryer and more seasonal than surrounding areas. The predicted probability of occurrence was low outside a narrow range of mean annual temperatures of 17.5–20°C. Within the area predicted to be climatically most suitable, records of Bush-crows were concentrated in 1-km cells of marginally but significantly lower normalised difference vegetation index (NDVI), indicating a preference for areas of lower photosynthetic activity.  At a finer spatial scale within a 10-km2 intensive study site in the core of the species’ range, nests were located in 30-m cells of higher NDVI but always close to areas of lower NDVI. These areas of lower NDVI comprise open grassland, which standardised observations of individual birds showed to be the main foraging habitat. However, taller vegetation is also necessary for nesting and roosting; the average height of nests from the ground was nearly 5 m. Therefore, the species’ range appears to be defined primarily by a unique climate pocket within which it shows a preference for park-like habitats of grassland interspersed with taller vegetation, largely the result of clearance of vegetation by people and their associated grazers. The diet appeared unspecialised and a wide range of feeding methods was observed. Models estimate the species’ optimal climatic range to cover around 6,000 km2, of which perhaps 4,500 km2 has suitable land cover. We tentatively estimate the global population to be at least 9,000 breeding pairs, with a potentially larger additional population of non-breeding birds, particularly nest-helpers. Several climate models predict increases in both temperature and  precipitation in the southern highlands of Ethiopia. The species’ narrow climatic range suggests that global climate change may therefore pose a serious threat to its long-term survival.

* Donald, P. F., Gedeon, K., Collar N. J., Spottiswoode, C. N., Wondafrash, M. & Buchanan, G. M. 2012: The restricted range of the Ethiopian Bush-crow Zavattariornis stresemanni is a consequence of high reliance on modified habitats within narrow climatic limits. Journal of Ornithology 153: 1031-1044.

Endemic Birds on the Horn of Africa

Ethiopia is characterized by a great topographic and landscape diversity. The height profile varies from 125 meters below sea level in the Danakil desert to the 4,533 m high summit of Ras Dejen in the Simien mountains. With an area of 1,127 million km² Ethiopia is something three times as large as Germany, with a comparable population of currently around 85 million. The peculiarity of the Ethiopian avifauna can be judged better when viewed in a somewhat wider context. As a spatial reference point should serve the "Horn of Africa", in addition to Ethiopia including its neighbors Eritrea, Djibouti and Somalia, as well as the Socotra Archipelago (short Socotra), lying off the Somali coast, but politically belonging to Yemen.

In this region more than 1,000 nesting and migratory bird species were noted. In the Endemic Breeding Birds table overall 67 species or taxonomic units are listed, which may be awarded the status of "endemic" on the Horn of Africa. Such a list is always provisional and can not offer more than a basis for discussion. This is due to the fact that a number of taxonomic and nomenclatural issues are still unclear. New findings inevitably lead to other perspectives and revised figures. Secondly, there is always a certain discretion whether to record a species with very small area units (or occasional occurrence) in neighboring countries in such a list or not. The table includes the IUCN Red List category, population size and trend for each species.