Undertaking a Grevy’s zebra census needs much effort due to the fact that the range of this endangered species stretches to 25,000 km2 and a way around this involves getting the general public on-board. Citizen scientists gathered together in Laikipia, Samburu, Isiolo and Marsabit for the 2018 edition of the Great Grevy’s Rally, the biennial photographic census organized to ensure that the population is sustaining itself after the last counting exercise.

The re-census held between 28th and 29th January 2018 aimed at finding out if the population was stable despite the natural and man-made challenges that plagued the species since the last count in 2016. Severe droughts leading to competition with livestock for dwindling pastures and diseases had been on the rise as had been poaching therefore necessitating the need to know how the population had fared on. This time round, 212 photographers in 143 vehicles joined in and another threatened species that neighbors the Grevy’s zebra was added to the mix: the reticulated giraffe. Teams made up of members of the public, conservancy members, rangers and scouts from conservancies and National Parks and Reserves, government officials from the counties as well as KWS and academic scientists participated in an area divided into 45 blocks and spent two consecutive dates driving to each block and snapping as many images as they could of the zebras.

The teams managed to capture nearly 50,000 images, an increase from the 40,000 taken in 2016. These were sent to the IBEIS/WILDBOOK hotspotter team at Princeton University for further analysis. Using their detection algorithmic pipeline, the images fit for analysis that clearly showcased the animals unique stripe patterns were filtered down to 22,918 for the Grevy’s zebras and 18,008 for the reticulated giraffes. This algorithm could determine whether the individuals snapped were new or if they had already been sighted previously. By using their “sight-resight” formula, the scientific team was able to give an estimate of the population sizes throughout the country and by county.  

On June 23rd  2018, the findings of the census were released to the public at the Great Grevy’s Ball hosted at the Fairmont Mount Kenya Safari Club in Nanyuki and they were encouraging:

  • Comprising 70% of the entire population, the adult survival rate was still at a high while recruits (infants and juveniles) made up the remaining 30%. However, there was a decline in the percentage of foals identified from approximately 11% in 2016 to approximately 5% in 2018 signaling the effects of the triple threat that was endured.

  • However, the overall number of the Grevy’s zebras had grown from the 2350 reported in 2016 to 2812 in 2018, an increase of nearly 300 new individuals! .As had been hoped, the population was indeed stable despite the harsh challenges. Significant rises were witnessed in Isiolo and Marsabit counties thanks to the fact that more teams were dispersed to these areas where the population of the zebras is sparser and the routes were traversed repeatedly. This contributed to sightings of individuals that were missed in the 2016 census.

For the reticulated giraffes, the first population count estimated their numbers to lie in the region of 2309 ± 332 individuals with Laikipia recording the highest density at 60%.    

The event was a culmination of the momentous collaborative effort between citizen scientists and conservationists to safeguard the future of one of Kenya’s unique species. You can download the full report here.