The Great Grevy’s Rally 2018: The Whys, Hows, and Wheres

The Grevy’s zebra, Equus grevyi, is the largest wild equid, or member of the horse family. With it’s large stature, thin elegant stripes, and general nonchalance in the face of danger, it’s easy to see why this zebra is also known as the imperial zebra. Compared to the common zebra, the Grevy’s is larger, has larger “Mickey mouse” ears, and has thinner stripes that don’t go around the belly.

The Zebra is named after Jules Grevy, president of France in the late 1800s, who received a stallion as a gift from the government of Abbysinnia, now Ethiopia. A widely circulated story names Menelik II as the generous gifter, although Menelik only took the reigns of the empire from Yohannes IV in 1889, seven years after the zebra was named. One anecdote has it that scientists sent a sample of the skin of the zebra to museums labeling it ‘Grevy’s zebra’, thereby giving it its name. Another version of events has it directly named by French naturalist Emile Oustalet in honour of the president. Regardless of its etymology, the unassailable truth is that this zebra species has experienced a drastic reversal in fortunes since the heights it attained during this imperial period. This is why scientists from all over the world and hundred of local citizen scientists are currently planning the second edition of the Great Grevy’s Rally, a two-day event in Northern Kenya designed to provide accurate estimates of the current numbers and distribution of this majestic species.

The Why

In addition to being rare, this species is also endangered, with current numbers only sustained by conservaton efforts in Kenya and Ethiopia, where it is protected legally. From an estimated 15,000 Grevy’s in the 1970s, there are now less than 2,500 Grevy’s zebra left in the wild. This meteoric decline can be attributed to hunting by humans, habitat loss, and foal predation. Of these, habitat loss is the most unforgiving culprit, with rangeland degradation in Northern Kenya and Southern Ethiopia proving especially catastrophic. Conservation efforts and policy interventions can only be designed and properly monitored and evaluated if accurate population numbers can be obtained. Counting Grevys in the wild is notoriously diffficult and even aerial counts are often confounded by temperatures, as zebras will often clump under trees when it gets hot, making counting them accurately near impossible. The GGR therefore offers an ooportunity to get accurate numbers, all the while visiting amazing landscapes and experiencing the vibrant local cultures in the oft-overlooked North.

The How

The GGR employs a scientific method known as the Capture-recapture, mark-recapture, or sight-resight principle. In this method, a population is sampled at a point in time and all individuals captured marked and released. At a subsequent point in time, usually soon enough that not a lot of births and deaths have occured, the population is sampled again. The number of animals that were marked during the first sampling that are also present during the second sampling allow an estimation of actual population size. With Grevy’s zebra, the sight-resight method is made easy by the fact that Grevys zebra stripe patterns are unique to individuals, and no two animals have a similar stripe pattern. Processing and identification of unique patterns is done through photographs taken during the rally. Identification is carried out by the Image Based Ecological Information System, IBEIS. IBEIS is a computational system that uses an algorithm to match images from any striped, spotted, or patterned animal. This system allows scientists to identify unique animals photographed on day one, unique animals photographed on day two, and the number of repeat sightings between day one and day two. These numbers are then entered into a formula known as the Lincoln-Peterson formula, which then gives an estimate of the total population:

The where

The 2018 GGR is being conducted in 5 counties across northern Kenya, on a multitude of ranches, private and community conservancies, and National Parks and Reserves across Samburu, Laikipia, Meru, Isiolo and Marsabit, on the 27th and 28th of January. Teams will meet in Nanyuki on Friday to receive their briefings and packets, and then proceed to campsites and lodges across the region. They will then take photos of all Grevy’s zebra encountered in their assigned blocks, making sure to take photos of the right flanks only. The second day will see teams drive the same routes as day 1, trying as much as possible to cover the same areas with the same effort. Monday the 29th will then see all teams return their cameras and extra SD cards, and get debriefed at the Nanyuki Sports club.

Giraffe join the fray

This year, in response to an increasing number of surveys showing reducing numbers of the reticulated giraffe (Giraffa camelopardis reticulata), the GGR will be incorporating this species into the photo count. This giraffe species can be found in South-western Somalia, southern Ethiopia and Northern Kenya. Also known as the Somali giraffe, the reticulated giraffe has very well-defined spots on its coat and has a uniform brown colour. The separation between the spots are narrow and well-delineated white gaps, resulting in a pattern resembling polygons.

How to participate:

A few spots remain for citizen scientists, mostly in Laikipia. Check out the options here.

For more information, visit the GGR page:

For more info on Grevy’s zebra and the work being done to conserve them, visit:

For more information on the Giraffe, visit:

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