First of all, the black rhino is not black, just as the white rhino is not white, but rather they are a worn grey. The main difference between the two species is in the shape of the upper lip: one is hooked while the other is square. Humans are the only real threat to black rhinos and they are still critically endangered. Between 1960 and 1995, their numbers dropped by a sobering 98%. Thanks to conservation efforts, the population has risen again to around 5000 today.