Bush-crow diaries: The mystery of the Abyssinian Pie

Image-2 Ethiopian-Bush-crow.1Located in the Tropic of Cancer, Ethiopia sits as a huge corner stone in the Horn of Africa, the easternmost projection of the continent. In this, the historic land of the Berbers, Ethiopia is renowned for its independence and depth of culture, the only African nation (at the time Abyssinia) alongside Liberia to retain national sovereignty during the ‘Scramble for Africa’. Ethiopia straddles the Great Rift Valley, carving its way from the Gulf of Aden and the Red Sea in neighbouring Djibouti, southward to Kenya and onwards through East Africa. This area is home to some of the most significant archaeological discoveries of early hominids, earning it the title of ‘the cradle of mankind’. In all this depth of heritage and geographical history, it is hardly surprising to think that Ethiopia is of high biological interest as well.

Ethiopia is split into a number of distinct biogeographical regions and habitat types, such as the Ethiopian highlands in the centre and West of the country and the arid steppe and deserts that typify the East, more akin to neighbouring states such as Somalia. Large numbers of endemic flora and fauna inhabit these unique habitat types such as the highly threatened and enigmatic Ethiopian Wolf Canis simensis, Africa’s only wolf species. Such levels of uniqueness might well be expected in specific and restricted habitat types, but in the region around Yabello, Oromia, in south of the country, living in a tiny area of some 6000km2 of heavily human modified rangeland and thornscrub, lives one of Africa’s best kept biological secrets. A bird described as ‘one of the most remarkable African discoveries of the twentieth century’ – the Ethiopian Bush-crow Zavattariornis stresemanni.
Discovered in 1938, the species name stresemanni was assigned in commemoration of the influential 20th century German ornithologist, Erwin Stresemann. This gives the species its other commonly used vernacular name of Stresemann’s Bush-crow, although (less commonly) it is also known as the Abyssinian Pie. As its vernacular name suggests, the species is assumed to be a member of the crow family Corvidae, but this has been widely debated in taxonomic circles. Currently it sits in its own unique genus with genetic analysis revealing its evolutionary history to be more related to that of the Asian ground-jays (Podoces sp.).

Its evolutionary history is interesting, but the explanation of its range restriction, with vast areas of seemingly suitable, unoccupied habitat existing directly adjacent to the species tight range, is nothing short of remarkable. One of the earliest ornithologists studying the species wrote, ‘The reason for this remarkably restricted distribution is not at all apparent to me. There seems to be nothing at all unique or distinctive about its environment’. This riddle was finally unearthed and released to the ornithological world in 2012 where models using climate variables predicted the bush-crow’s range perfectly, suggesting its current area of occupancy is delimited by a climate envelope that harbours a cooler, dryer and more seasonal climate than its surrounding area.
Adding to the complexity of the situation, bush-crows appear unspecialised in their diet and rely heavily on traditional Borana pastoral rangeland for their survival. Increases in agricultural land, intensification of grazing regimes and a growing human population throughout its range have led to changes in land cover and subsequently to the degradation of the rangeland it depends on. Currently listed as ‘Endangered’ on the IUCN Red List of threatened species, land–use change appears to be the major threat to the species survival in the short-term, whereas the looming threat of anthropogenic climate change remains an unevaluated longer-term threat.

Virtually nothing is known about their ecology in relation to the unique climate bubble defining their presence. Determining the ecological mechanisms that underpin this range restriction has been identified as a research priority to inform how best conservation action can be directed on the ground, both physically and logistically.
For the next eight weeks I will be gathering baseline data on the ranging behaviour and foraging ecology of the species, drawing comparisons between the extremities and core areas of its range. Firstly, this will focus on catching, colour-marking and obtaining standard biometric measurements for the first time. After a settling period of a few weeks, birds will then be re-found to collect data through observational follows on marked individuals. As anyone who has conducted fieldwork will know, plans are always subject to adaption or change however!

What the outcomes will be is anyone’s guess, but in the words of Gedeon (2006) ‘It is not only its comparatively recent discovery that makes the Ethiopian Bush-crow one of the most remarkable African birds. Its exceptionally interesting biology, and the acute threat to its habitat, should place it clearer than it has been to date in the focus of international research and conservation.’

I hope you will join me on the journey into the horn of Africa, its culture, natural history and life in the field, as we attempt to tease out more information and gradually unravel the mystery of the Abyssinian Pie.

Source: Scientific American

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