The thunderous calls of widespread hippos might be heard from greater than half a mile (1 kilometer) away — and when a hippo hears the booming name of an unfamiliar hippo, the animal usually responds by letting free a dramatic spray of dung.
Hippos (Hippopotamus amphibius) spray dung as a method to mark their territory, however till now, scientists did not know that an unfamiliar hippo’s name might provoke this conduct in one other hippo. In a brand new research, printed Monday (Jan. 24) within the journal Present Biology, researchers noticed hippos on the Maputo Particular Reserve in Mozambique and located that the animals acknowledge and reply in another way to the calls of various hippos within the space, relying on whether or not these hippos reside in the identical territory, a neighboring territory or someplace farther away.
Particularly, the hippos might differentiate a well-known hippo from a stranger by the sound of their “wheeze honk,” the animals’ signature name.
Associated: Gallery: Evolution’s most excessive mammals
“The wheeze honk is acknowledged because the attribute name of the hippo, consisting of a better pitched ‘wheeze’ adopted by a number of ‘honks,'” stated Maria Maust-Mohl, an affiliate professor within the psychology division at Manhattan School in New York Metropolis, who research animal communication and was not concerned within the research. That preliminary “wheeze” swells shortly and loudly, just like the sound of a trombone, and the “honks” that comply with sound kind of like a deep, throaty snicker.
Hippos usually produce wheeze honks similtaneously others of their social group, as if in refrain, and appear to sound the decision in response to adjustments of their atmosphere, Maust-Mohl advised Dwell Science in an e mail. Because of this, it is thought that the wheeze honk could also be a key ingredient of hippo social communication, Maust-Mohl and her colleagues reported in a 2015 research printed in The Journal of the Acoustical Society of America. Now, the brand new research reveals how wheeze honks could assist hippos outline their social teams and distinguish good friend from foe.
“As a territorial species, it could not be uncommon for hippos to have tailored this means to tell apart and react in another way to hippos which may be extra acquainted versus these which may be extra of a menace,” Maust-Mohl stated. “The findings of this research recommend the wheeze honk could serve to assist hippos decide the presence and id of different hippos close by, in addition to talk inside and between teams of their shared habitats.”
However though the research outcomes are intriguing, “I believe the pattern dimension is a bit small,” stated Camille Fritsch, a postdoctoral researcher on the College of KwaZulu-Natal in South Africa, who research hippo behavioral ecology and was not concerned within the research. The analysis needs to be repeated in bigger teams of hippos, in numerous habitats and at totally different occasions of the 12 months, for the reason that distribution of hippos shifts between the moist and dry seasons, he stated. “It is going to undoubtedly result in additional research.”
Hippos feed at evening, consuming as much as 80 kilos (35 kilograms) of grass every night, and the large herbivores collect in our bodies of water through the day, forming teams that sometimes encompass a dominant male, a variable variety of females and juveniles, and some peripheral males.
“On the identical lake, a number of teams, or pods, can cohabit,” Nicolas Mathevon, a co-senior writer of the research and director of the Sensory Neuro-Ethology Crew on the College of Saint-Etienne in France, advised Dwell Science in an e mail. “Once we determined to check hippos, a query instantly arose: can they acknowledge one another by voice?”
To reply this query, the staff recorded wheeze honks from seven totally different teams of hippos residing on lakes on the Maputo Particular Reserve. The group sizes ranged from three people to 22. With these recordings in hand, the staff then arrange audio system close to every hippo group’s habitat, positioned about 230 to 295 toes (70 to 90 meters) away from the animals, and performed again the sounds.
The hippos reacted to the recordings by producing their very own wheeze honks, approaching the audio system or marking their territory with feces, or by displaying a combination of those behaviors — however their responses diversified relying on which recording was performed, the staff discovered.
The hippos confirmed the least response to calls from people inside their group, and reacted barely extra strongly to people from neighboring teams on the similar lake, the staff discovered. These responses sometimes solely included wheeze-honking and approaching the speaker, and included little to no marking. However the animals persistently confirmed the strongest response to calls from strangers and marked way more usually in response to those sounds.
It is smart that hippos would present much less aggression in the direction of hippos they know, Fritsch stated. The dimensions of hippos’ social teams develop and shrink with the altering seasons; as water assets change into scarce within the dry season, small teams of hippos collect at one water supply and merge right into a single, giant group, Fritsch stated. “They’ve some understanding of who’s round them. And due to this fact, it could make sense that they’re much less aggressive in the direction of these people,” he stated.
It might be attention-grabbing to see if and the way these social dynamics change over time, as hippo teams transfer round and their densities skinny out or develop extra concentrated, he stated. It might even be attention-grabbing to repeat the experiment with hippos residing in numerous habitats, akin to rivers and floodplains, fairly than lakes. The brand new research, though considerably restricted, opens the door to research these extra questions, he stated.
In the long run, this line of analysis might assist conservationists higher defend hippo populations, Mathevon stated. For instance, within the occasion that conservationists have to relocate hippos to a brand new habitat, “it could be doable to get the native hippos used to the voice of the brand new ones earlier than they arrive, and vice versa,” Mathevon stated. After all, hippos should be provoked by the sight or scent of an unfamiliar hippo, even when they acknowledge the sound of their voice. However introducing the voice forward of time should assist, he stated.
“Though hippos aren’t listed as endangered, their populations are declining quickly,” Maust-Mohl stated. “Future research of their conduct and communication may also help enhance the administration and conservation of this species by permitting us to higher perceive the character of their social teams.”
Initially printed on Dwell Science.