Researchers observed an unusual behavior among male Amazon river dolphins, known as botos, where they flip onto their backs and urinate into the air, a phenomenon termed "aerial urination." According to Popular Science, this behavior appears to serve a social or communicative purpose among these aquatic mammals.
The research team from the CetAsia group documented this behavior over 219 hours of observation in the Brazilian Tocantins River. They recorded 36 instances where male botos rolled onto their backs and released jets of urine into the air, reaching distances of up to 91 centimeters.
"On the first occasion, we saw a male flip his belly up out of the water, expose his penis and then proceed to urinate into the air. We were really shocked, as it was something we had never seen before," said Claryana Araújo-Wang, one of the researchers, according to Popular Science.
Other male dolphins often approached the floating urine jet, touching it with their snouts to study the message. Sometimes they seemed to chase the stream, suggesting they actively engage with the urine as a form of communication. As reported by Cursor Info, nearby male dolphins sometimes remained in place, while in other instances, they pursued the urine trajectory using their snouts or rostrums.
Researchers suggest that the bristles on the dolphins' snouts likely act as chemical sensors, helping them pick up signals from their environment and decode messages in other botos' urine. This mechanism is similar to the olfactory communication of terrestrial animals, such as wolves or ungulates, but adapted to life in an aquatic environment.
In the animal world, urination often serves a signaling function. Many terrestrial animals, such as dogs, cats, and bears, use urine to communicate information about health status, social position, or readiness to reproduce. In aquatic environments, the use of urine for communication is less common but not unique. Dominant male African cichlid fish interpret urine pulses as signals related to reproduction and territorial information. Similarly, the narrow-clawed crayfish urinates as a sign of aggression.
"This behaviour will require more research; however, we hypothesise that aerial urination helps in advertising male quality in terms of social position or physical condition," Araújo-Wang told BBC Wildlife.
The scientists suggest that because aerial urination in Amazon river dolphins has only been observed in males, it may be socially learned—picked up through observation of other peeing male botos.
A study from Stephen F. Austin State University in Texas confirmed that bottlenose dolphins use their tongues to identify other cetaceans through the taste of their urine.
It was previously believed that dolphins primarily navigate using echolocation and visual perception. However, underwater vision is poorly developed in Amazonian dolphins, making tactile and chemical perception especially important. This suggests that the unusual behavior observed may play a role in their social interactions. "Aerial urination likely serves a social function beyond waste elimination," the researchers concluded.
The article was written with the assistance of a news analysis system.