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The Great Grevy's Zebra Rally - The Results Are In!

September 06, 2016

On the 30th and 31st of January this year, citizens, scientists and conservationists came together to count and collect photographic data on the world's rarest zebra, the Grevy's, a species that almost exclusively is now found in the Laikipia-northern Kenya ecosystem. 

The Grevy's zebra - easily distinguished by its thin, elegant stripes, striking frame and gait - once freely roamed much of northern Kenya, southern Ethiopia and western Somalia. In Kenya alone, it is estimated we had as many as 15,000 individuals in the 1970s. Until now, it had been difficult to know exactly how many Grevy’s zebra exist in the country and counting them has always posed a challenge. Historically, they have usually been counted from the air, but detecting them can be problematic as they like to shade under trees in the heat of the day.

To get a better estimate, the Kenya Wildlife Service’s Grevy’s Zebra Technical Committee recommended carrying out a ‘Sight-Resight’ analysis by amassing a large number of volunteers to drive throughout the Grevy’s zebra’s range, taking pictures on two successive days and then using the newly developed IBEIS software (4,5) to identify and match individual zebras based on ‘hotspots’ created by each individual’s unique stripe patterns. In this way the problem of past counts and censuses could be overcome yielding a more accurate estimate of population size both nationally and by counties and ecologically relevant regions.

Performing the census required a herculean effort since Grevy’s zebras range over 25,000 km2. It was solved by involving the general public. The first ever initiative of its kind for this endangered species, dubbed the Great Grevy's Rally, saw 118 teams participate in photographing and counting Grevy's zebra across vast landscapes - from Lewa to Loisaba, Westgate Community Conservancy to Sera, these groups, comprising of close to 500 people, some of whom rarely get to interact with wildlife, enthusiastically became citizen scientists for two days. The images taken by the citizen scientists in January were analysed by the IBEIS/ WILDBOOK team at Princeton University. 

The Results

The results of the census were announced at the Great Grevy's Ball in Nanyuki on the 3rd of September, in a fun evening attended by the Head of the Kenya Wildlife Service, Kitili Mbathi, county governments representatives, US Ambassador Robert Godec, conservationists including the Lewa Team, Princeton University, citizen scientists and the public.

The results revealed that over 40,000 images were taken. From these data, three major findings emerge. 

First, this approach estimated that Kenya’s total Grevy’s zebra population consists of 2250 individuals ranging from a low of 2157 and a high of 2343 individuals. The Princeton team then had to include Grevy's zebra that weren't counted, either due to accessibility or security issues. They estimate this came to 100 individuals. This means the population of Grevy's zebra across Laikipia, Meru, Samburu, Isiolo and Marsabit counties comes to 2,350 individuals

What is most interesting is that Laikipia county, once considered a refuge, is now home to the largest population of Grevy’s zebras in Kenya.

Second, the demographic state of the national population and most counties are healthy. When the percentage of infants and juveniles approaches 30% of the total, populations appear stable and tend to sustain themselves because there are sufficient recruits to replace adults that die.

Only Meru County’s Grevy’s zebras do not approach this critical threshold, whereas both Samburu and Laikipia counties surpass it.

Third, the fraction of females giving birth per year is high, or its inverse, the inter-birth interval is low. Both also indicate that the reproductive potential of a population is strong and steady. 

The population on Lewa, counted annually, was estimated to be at 336, plus or minus 26. This is slightly more than our estimate from the game count this year. 

Collaboration in Conservation - The Future

The Great Grevy’s Rally has not only provided conservationists and scientists with staggering results to inform management decisions for the endangered species, it also created an opportunity to demystify scientific research to the public. It provided an exciting chance for citizens, residents and visitors to share in the science of discovery and to ask questions that will contribute to research and management of one of Kenya's most threatened but least known species.

A culmination of unique partnerships involved in ensuring the survival of this magnificent animal, this certainly signals the future for conservation in the country where citizens, conservationists, scientists, governments and communities rally together to save an iconic species.

The Great Grevy's Rally was spearheaded by the Grevy's Zebra Trust and Laikipia Wildlife Forum in collaborative effort between Lewa, NRT and the community conservancies, the Kenya Wildlife Service, Marwell Wildlife, Princeton University, county governments of Laikipia, Isiolo, Marsabit and Meru, and many others.