Hippos can communicate with one another and tell the difference between the honking sounds of their friends, neighbours and strangers, a study has found.A team of researchers from the University of Saint-Etienne in France recorded random vocalisations made by groups of hippos at the Maputo Special Reserve in Mozambique. This area features a host of lakes and different hippo populations, and the researchers played back some of the recordings to the groups using speakers. They focused on what scie