Ethiopian Bush-crow and thermal adaptation

Ethiopian Bush-crow: Naked skin area could serve thermoregulation

The Ethiopian Bush-crow Zavattariornis stresemanni is an extremely range-restricted Ethiopian endemic that is confined to dry and relatively cool south Ethiopian acacia savannah habitats. It has been assumed that the specific temperature conditions in these areas might reflect a temperature optimum to which these birds have adapted. With non-tropical magpies Pica and ground-jays Podoces being among their closest relatives, bush-crows might have developed particular adaptive traits to persist under the tropical conditions of the south Ethiopian plains. However, this thermal adaptation hypothesis has not been tested so far. Using an infrared thermography system we investigated if bush-crows are able to regulate their body temperature by emitting heat.

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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.

Masked Lark records 2011 in southern Ethiopia

Singing Bush-lark (Miafra cantillans) in Sarrite, Southern Ethiopa 

According to Ash et al. (2009) there have been only 5 Masked Lark Spizocorys personata records (altogether 18 birds) in Ethiopia in more than 110 years. In Kenya only 3 sites are known. That's worldwide only 9 known locations with four subspecies. The range is said to be 73,300 km², but probably much smaller and fragmented. Nevertheless, the BirdLife model map shows a nearly coherent and widespread distribution, which does probably not exist in this way. There is a need for research, not least because the future outlook for this species seems to be very critical due to climate change.

In southern Ethiopia the subspecies Spizocorys personata yavelloensis has been scientifically described around 70 years ago. Since then apparently no other reliable data exist on the presence of this subspecies near the place of origin.  A search in June 2011 provided, however, positive results. An encouraging large number of Masked Larks were found in an area about 80 km west of Yabello. The area is also habitat for Grevy's Zebras and intended to be part of a prospective National Park. The most common lark in the area, however, is the Singing Bush-lark (figure).

Avifauna of Ethiopia: Some risk aspects

Threatened animal species in Africa (WCM/IUCN 1998) 

Many of the endemic species in the Horn of Africa live in very narrowly defined areas. 30 of 67 species in the Endemic Breeding Bird table inhabit areas of less than 20,000 square km, eight of them even in areas of 200 square km or less. Therefore, the risk potential of these species must be assessed as high. Regional and even local changes in land use or climate conditions can have serious consequences for the development and survival of small populations.

According to IUCN, 17 of the 67 endemic bird species are considered as "endangered", three of them as "critical endangered": Ochre-brested Francolin (Francolinus ochropectus), Archers's Lark (Heteromirafra archeri) and Liben Lark (Heteromirafra sidamoensis). The latter exists only in an approximately 30-acre area in southern Ethiopia. The total population size is estimated to be less than 250 individuals (Donald et al. 2010). If no protection measures are implemented in the near future, we will probably witness its extinction. Encouraging are recent observations from May 2011, after which the species occurs in another small area in north eastern Ethiopia (Nigel Collar, oral information). Genetic studies should also clarify whether H. archeri and H. sidamoensis are actually different taxa.

Looking at the birds of the African continent as a whole, the avifauna of Eastern Africa (including Horn of Africa and offshore islands) is particularly at risk. Back in the nineteen nineties, 107 bird species in that area were threatened according to IUCN criteria (critical endangered, endagered or vulnerable ). That's more than 50% of then 207 threatened bird species in Africa (WCM / IUCN 1998).