When hippos sense danger, they release a flurry of faeces

It responds differently when a hippo hears a call from a familiar or unfamiliar hippo.

 

Hippo cries can be heard from over 0.6 miles (1 km) away, and when one hippo hears the booming call of another hippo, it may answer with a dramatic spray of poo.

 

No one knew before that hearing the call of a different hippo could cause another hippo to spray excrement to claim its territory, but that's exactly what happens when hippos (Hippopotamus amphibius) meet for the first time. Hippos at the Maputo Special Reserve in Mozambique are territorial, responding differently to the calls of other hippos depending on whether they live in the same territory, a neighbouring territory, or further away, according to a new study published on Monday (Jan. 24) in the journal Current Biology.

 

Hippopotamuses had a unique call known as a "wheeze honk," Other hippos could recognise this call and know who was around.

 

According to Maria Maust-Mohl, an associate professor in the psychology department at Manhattan College in New York City who studies animal communication but was not involved in the study, "the wheeze honk is recognised as the characteristic call of the hippo, consisting of a higher pitched 'wheeze' followed by several 'honks.'" The first "wheeze" builds swiftly and loudly, like a trombone, and the subsequent "honks" are somewhat reminiscent of a deep, throaty laugh.

 

According to an email exchange between Maust-Mohl and Live Science, the hippo population often produces wheezing honks in unison, as if in chorus, and appears to sound the cry in response to environmental changes. According to research by Maust-Mohl and coworkers published in The Journal of the Acoustical Society of America in 2015, the wheezing honk is likely an important part of hippo social communication. The latest research shows that wheezing honks may assist hippos in establishing social hierarchy and identifying friends from foes.

 

Hippopotamuses "being a territorial animal, it would not be surprising for them to have acquired this ability to discriminate and react differently to hippos that may be more familiar or more of a threat," Maust-Mohl said. The results of this study imply that hippos use the wheeze honk to communicate among and between groups in their common habitats, as well as to detect the presence and identify the identity of other hippos in the area.

 

Camille Fritsch, a postdoctoral researcher at the University of KwaZulu-Natal in South Africa studying hippo behavioural ecology, remarked, "I think the sample size is a bit tiny," despite the study's novel conclusions. He suggested that since the distribution of hippos changes between the wet and dry seasons, the study be repeated with larger groups of hippos, in other habitats, and at different times of the year. In other words, "it will undoubtedly lead to more research."

 

Although hippos are nocturnal feeders, consuming up to 35 kilogrammes (80 pounds) of grass each night, the giant herbivores congregate in bodies of water during the day, forming groups that generally include a dominating male, a variable number of females and juveniles, and a few periphery males.

 

"On the same lake, various groups, or pods, can cohabit," Nicolas Mathevon, co-senior author of the study and director of the Sensory Neuro-Ethology Team at the University of Saint-Etienne in France, told Live Science in an email. When we chose to research hippos, one of the first questions we had was whether or not they could identify each other by their calls.

 

The researchers set out to discover the answer to this mystery by recording the wheezing honks of seven distinct hippos in the lakes of the Maputo Special Reserve. Miguel Gonçalves, the reserve's park warden, told Live Science in an email that hippo populations on the reserve typically range from 10 to 25 individuals, depending on the terrain.

 

Using these recordings, the scientists placed speakers near each hippo group's habitat, around 230 to 295 feet (70 to 90 metres) away from the animals, and played back the noises.

 

The scientists discovered that the hippo's responses varied according to the audio played. The hippo responded with its wheezing honks, approaching the speakers, marking its territory with faeces, or a combination of these behaviours.

 

The researchers observed that the hippos responded least to calls from members of their own group and slightly more strongly to calls from members of other groups at the same lake. Wheezing, honking, and walking over to the person speaking were about the only markings on these replies. However, the animals were marked significantly more frequently in response to calls from unknown sources.

 

According to Fritsch, hippopotamuses are less likely to be aggressive toward other hippopotamuses if they are familiar with them. As described by Fritsch, Hippo social groupings fluctuate in size with the seasons, with smaller groups merging into larger ones during the dry season when water is limited. "They can make some sense of the people around them." "Those are his words."

 

It would be intriguing to observe whether or not these social dynamics shift over time, he said, as hippo groups relocate and population densities fluctuate. It would be fascinating to try the same thing with hippos from a variety of other environments besides lakes, such as rivers and floodplains. He noted the study's limitations; it paves the way for further research into such issues.

 

Mathevon believes that this line of inquiry may one day contribute to the efforts of conservationists to save hippo populations. If conservationists need to move hippos to a new habitat, "it may be feasible to get the local hippos accustomed to the voice of the new ones before they arrive, and vice versa," Mathevon added. While hippos can distinguish the sound of another hippo's speech, they may still be agitated by the appearance or smell of a stranger. However, he added that there was still a chance that introducing the voice in advance would be helpful.

 

Gonçalves agreed that learning more about how hippos talk to one another would be useful for planning translocations if they were ever needed at the reserve. He added that the study's findings might one day help scientists evaluate the density of a hippo group based on the quantity of sound it produces, among other applications.

 

However, within the borders of the Maputo Special Reserve, estimations imply that the local hippo population is now expanding, as highlighted by Gonçalves. Although hippos are not designated as endangered, their populations are dropping rapidly, Maust-Mohl remarked. Maust-Mohl argues that a better understanding of the nature of their social group, thanks to future research on their behaviour and communication, is crucial for managing and conserving this species.

Reference : https://www.livescience.com/hippos-recognize-voices-spray-poop-for-strangers

Image source : https://pixabay.com/id/photos/kuda-nil-mendengus-sungai-2834884/

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