研究發現河馬可以區分來自朋友、鄰居及陌生河馬的叫聲。 當牠們聽到來自另一個更遠群體的叫聲時，牠們會被激怒並以更響亮的叫聲回應，及強烈四處噴灑糞便作為領土標記。 這項行為研究對保育工作非常重要及有幫助，尤其是在重新安置河馬方面。

Study found hippo can distinguish calls from friends, neighbors and strangers. When they hear calls from strangers from a more distant group, they will be provoked and responded strongly with louder calls and spraying dungs all over the place as territorial marking. This behavioral study is important and beneficial to conservation works especially when relocating hippos.

https://www.treehugger.com/hippos-recognize-wheeze-honk-strangers-friends-5216927