By Monicah Mwangi2 Min ReadSlideshow( 5 images) MAASAI MARA, Kenya( Reuters)-In Kenya’s Maasai Mara National Reserve, the Toyota 4x4 Landcruiser of tour guide and driver Sylvester Mukenye glides silently past a herd of grazing elephants, then past a pride of lions lying in the grass. The animals are completely unperturbed by the proximity of the vehicle because its diesel engine has been replaced by an electric one that eliminates the rumbling noise and, just as importantly, reduces the emission