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Slender-horned gazelles - How to count them in the Sahara?

22/04/2012 08:04:51

A fine herd of slender-horned gazelles in the Sidi Toui National Park in Tunisia (Photo: Tim Wacher)

Slender-horned gazelle - Ghost of the sands - Courtesy of  Sahara Conservation Fund

April 2012. Recently the Sahara Conservation Fund, the Zoological Society of London, and the Sahelo-Saharan Interest Group have participated in surveys of the slender-horned gazelle (IUCN ‘Endangered') in Algeria and Tunisia. Reconnaissance visits to the Algerian Erg Occidental and Erg Oriental were interspersed with camel-based surveys of the Tunisian sector of the Erg Oriental at Djebil, and most recently the Jabbes-Senghar National Park.

Mixed news - Heavily hunted, but still there
The news about this poorly known and very striking gazelle is mixed. Like ghosts of the sands, the ‘reem' as they are known in Arabic, are always elusive and difficult to see. In spite of this, our local Tunisian partners stress that almost everywhere the gazelles suffer from uncontrolled hunting, irrespective of their protected status.

Slender-horned gazelle. Photo: Tim Wacher

Slender-horned gazelle. Photo: Tim Wacher

Nonetheless, it is also true that, without fail, on fieldtrips to the margins of the great sand seas, fresh gazelle tracks have proved relatively easy to find. The circumstances prompt key questions. First, are we identifying these tracks correctly and not confusing them with the more widespread dorcas gazelle, which is also present at the edge of the ergs, though apparently less so in the interiors? And second, how can we find out what these observations mean in terms of numbers of gazelle?

The great difficulty with the second question is that the tumbling dune landscape favoured by well-camouflaged and very shy slender-horned gazelles, while offering memorable desert scenery, provides an almost impossible terrain for conventional ground-based survey methods, such as those we have used for dorcas gazelles in the far less sandy habitats of the Sahel. Perhaps the best option to establish numbers will be to conduct helicopter-based surveys.

Track surveys
In the meantime, however, we are making good progress with track interpretation. Slender-horned tracks are generally reckoned to be significantly larger than those of the dorcas gazelle, but until recently we had little or no solid data on how much larger and particularly on what degree of overlap might occur between the two species. To answer this question we are measuring footprints from known captive adult animals on similar substrate at the Sidi Toui National Park. The results show average hoof print size could be considered diagnostic in 14 out of 17 individuals measured, with one large dorcas and two smaller slenderhorned gazelles falling in a zone of overlap and uncertainty.

Widely distributed but uncommon
The study provides useful reassurance that for the most part we have not been confusing tracks of the two species. Since the tracks indicate that slender-horned gazelles are well distributed, if not common, this also confirms the value of attempting a helicopter survey to try and answer the bigger question of how many gazelles might be out there. The full results of this study can be downloaded from our website on the Reports pages.

The author of this article, Dr Tim Wacher, is a Senior Conservation Biologist with the Zoological Society of London.

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