In 2006, for six months, the NGO Symbiose and veterinarians Isabelle and Jean-François Lagrot with their local teams examined the common roaming ground of "Diceros bicornis longipes" in the northern province of Cameroon to assess the status of the last population of the western black rhino subspecies. For this experiment, 2,500 km of patrol effort resulted in no sign of rhino presence over the course of six months. The teams had concluded that the rhino was extinct approximately five years before it was officially declared so by the IUCN.