Grevy's Zebra Count - The Results Are In!

On the 30th and 31st of January 2016, the first ever citizen-driven census of an endangered species took place in northern Kenya. The Great Grevy's Rally saw 118 teams, comprising of approximately 500 people, take to the dusty roads of Samburu, Laikipia, Isiolo, Meru and Marsabit counties with one aim - to find and take photographs of as many Grevy's zebra as they possibly could. 

As it is difficult to get an accurate estimate of population sizes from aerial surveys, the only way to get a precise count was from mass participation on the ground. Citizen scientists covered over 25,000 square km; on private land, government parks and NRT community conservancies, and took more than 40,000 images with GPS enabled cameras. 


Great Grevy's Zebra Rally - The Numbers

  • 118 teams of citizen-scientists, comprising of approx. 500 people
  • 5 counties
  • 40,000 images taken, of thes;, 15,000 usable
  • 16,866 Grevy'z zebra in the photos
  • 1,942 individual Grevy's in the photos
  • Total population of Grevy's across the 5 counties, including those not photgraphed in the Rally, comes to 2,350 individuals

  • The results of the count were revealed at the Great Grevy's Ball, that took place in Nanyuki on Saturday 3rd September. The event was attended by participants, NRT member conservancy managers, and conservation organisations. Also in attendance was US Ambassador Robert Godec, who took part in the Great Grevy's Rally himself, as well as KWS Director General Kitili Mbathi, and Paula Kahumbu of Wildlife Direct. 

    The images taken by the citizen scientists in January were analysed by the IBEIS/ WILDBOOK team at Princeton University. Professor Dan Rubenstein of Princeton was at the Ball to announce the long-awaited results.

    Populations of Grevy's zebra in Laikipia and Samburu are growing.

    Populations of Grevy's zebra in Laikipia and Samburu are growing.

    Of the 40,000 photographs, 15,000 were usable (that is, the photograph was taken of the correct side of the animal, and were clear). In those usable images, there were 16,866 Grevy's zebra that needed to be identified. The IBEIS team used specially designed software (Hotspotter) to analyse stripe patterns, and managed to identify 1,942 individual Grevy's with timestamps and locations.

    From this data, the Princeton team could make an estimate of the population by looking at the number of zebras on day 1, multiplied by the number on day 2, multiplied by the re-sightings. They estimated 2,250 Grevy's zebra, plus or minus 93. This is the most precise population estimate the Grevy's zebra has ever seen (typical error bars are in the major hundreds) - and key to this was the re-sightings. 868 animals were seen on day 2 that were seen on day 1, that is 64%. Each of these animals was sexed and aged too. 

    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. 

    In NRT Conservancies - the focus will continue to be on restoring grasslands and improving water access for Grevy's.

    Thanks to the GPS cameras, this population can be broken down by county too:

    Isiolo - 268 ± 48 (where there are 5 NRT member conservancies)
    Samburu - 429 ± 70 (where there are 6 NRT member conservancies)
    Marsabit - 75 ± 27 (where there are 4 NRT member conservancies)
    Laikipia - 1,206 ± 60
    Meru - 332 ± 26 (where there are 4 NRT member conservancies between Laikipia & Meru)

    Encouragingly, the populations in Samburu and Laikipia were shown to be growing, with Marsabit and Isiolo not far behind. The Meru population has the lowest number of recruits (youngsters that survive to be a part of the breeding population) and this is down to the high numbers of predators in the county, particularly lion. 

    The data gathered from this momentous event will be used by all the organisations involved to shape conservation strategies. In NRT Conservancies - the focus will continue to be on restoring grasslands and improving water access for Grevy's. In other areas, such as Lewa, the focus will be on addressing high lion predation rates. 

    The number of Grevy's zebra in Kenya has declined from 14,000 in the mid 70's, to just over 2,000 counted this year. The Great Grevy's Rally was a collaborative effort between NRT and the community conservancies, the Grevy's Zebra Trust, the Laikipia Wildlife Forum, Lewa Wildlife Conservancy, Princeton University, and many others.