Predator Research on Lewa

A new and very interesting project initiated in 2003 here on Lewa Wildlife Conservancy and funded by Saint Louis Zoo has just clocked 1 year. The purpose of the project is to determine the impact of predation mainly by lion but also by hyena on the endangered Grevy's zebra and the more common Plains zebra.

Lion numbers have increased dramatically in the last two years from an estimated 12 to over 24 residents. In 2003 a coalition of six males known as 'Narc' arrived on the Conservancy. The resident lionesses have bred and there are 14 cubs less than 12 months old from 4 females, representing a significant population increase within a short time. Findings have shown that the recent increase in lion numbers is taking its toll on the Grevy's zebra. It appears that lion predation is having a major impact on the recruitment of young foals. However other age classes of Grevy's zebra have also been affected, though to a lesser extent.

We now have a total of four lion that are radio-collared on Lewa (2 males and 2 females). Due to the fact that we are dealing with a lion population that is in its infancy there is no typical pride structure as one would expect to see. So you typically find small groups of perhaps three males or a male and a female and her cubs, with each group represented by one collared lion. These lion are tracked on a daily basis and their location is recorded using a GPS and these are used to create maps showing lion movements within the Conservancy.

So far the project has identified a total of 24 resident lions (4 males, 6 females and 14 cubs). This figure excludes the migratory or transient lion from Borana and Il Ngwesi of which there are between 10 and 15. This has been achieved using the whisker spot technique and also by looking at associations by lion with our collared individuals. Each lion has a unique arrangement of whisker-spots, which are recorded and then the lion is assigned its own identification code (show photo of a lion and its associated whisker spots).

One very important facet to this project is looking at predator diet. Scat is collected from both lion and hyena. Found in the scat are hairs from the animal that has been predated upon. By extracting these hairs and observing them under a microscope it is possible to determine what prey species the hair belongs to, by comparing them to a reference hair collection, made up of hairs collected from both Plains and Grevy's zebra. This is a proven scientific method that allows us to identify which species the hair in the scat belongs to.

The population of Plains zebra on Lewa is between 2½ to 3 times that of Grevy's zebra and it is expected that predation on the two zebra species would be reflected in the same proportion. To date, over 500 hairs from 50 scats have been individually mounted and analysed. Results have shown that zebras form the main diet of lions. However, there has been a higher percentage of Grevy's than Plains zebra hair present in lion scat, implying that more Grevy's zebra are killed by lions that Plains zebra.

So, why is it that Grevy's zebra are preferred? Possible answers include: the overlapping range of the Grevy's zebra (especially females with foals) and core lion groups; higher vulnerability of foals because during the first three months of their lives they move little and may be left in nursery herds which make them more vulnerable; most of the Lewa Grevy's zebra have lived without predators until now so no practice on how to best avoid them and then if necessary fight them off was learned during ontogeny - we can expect this to change as the next generation matures; or, as Alistair McGowan remarked, perhaps it's because lion prefer gravy with their zebra!

Whatever the reason, predator research on Lewa is very important and it will become increasingly so with time particularly since it boasts ¼ of the world's remaining population of the Grevy's zebra. {Solutions to this conservation paradox may include the control of predator numbers through translocation and contraception programmes or the translocation of Grevy's zebra to safer areas.}