Scientists studying Amazon river dolphins, known as botos, have documented a peculiar ritual: males flip onto their backs and spray urine into the air. Researchers believe this unusual habit may serve as a form of social communication.
A research team spent 219 hours observing botos in the Tocantins River in Brazil. They recorded 36 males rolling onto their backs and releasing jets of urine, sometimes reaching nearly a meter in height.
Other male dolphins showed immediate interest, moving toward the floating urine and touching it with their snouts. Some appeared to follow the urine’s path, suggesting active engagement with the chemical signals it contained.
The behavior surprised researchers. “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,” said Claryana Araújo-Wang, a researcher involved in the study. “We were really shocked, as it was something we had never seen before.”
Urine as a communication tool
Urine signaling is common among land animals. Dogs, cats, and bears use scent to convey information about health, status, and reproductive readiness.
Aquatic species are less known for using urine in this way. However, some fish, such as African cichlids, rely on urine signals to establish territory and attract mates. Crayfish have also been observed urinating as a display of aggression.
Male dolphins have been observed shooting jets of urine into the air and other dolphins seem to follow the stream, perhaps to pick up social cues.pic.twitter.com/TFg1TNF67u
— Massimo (@Rainmaker1973) February 2, 2025
Amazon river dolphins seem to utilize urine for similar purposes. Scientists propose that the bristles on a dolphin’s snout may aid in detecting chemical signals, akin to scent receptors in land animals. This capability might enable males to acquire information about one another through urine.
A social learning behavior
So far, only male botos have been observed performing aerial urination. This suggests that the behavior may be social instead of instinctual. Younger dolphins could be picking up the habit of watching older males.
“We hypothesize that aerial urination helps in advertising male quality in terms of social position or physical condition,” researchers concluded in their study. They suspect it may help males advertise their strength, rank, or reproductive status within the group.
Beyond sound and sight
Dolphins are widely known for using echolocation and vision to navigate their surroundings. However, Amazon river dolphins have poor underwater vision, making chemical and tactile perception more important.
A study by Stephen F. Austin State University in Texas found that bottlenose dolphins can recognize each other by tasting urine. This finding supports the idea that chemical signals play a larger role in dolphin communication than previously thought.
With more research, scientists hope to understand this behavior’s purpose and role in the Amazon River dolphin society.
The discovery adds to growing evidence that dolphins rely on multiple senses beyond sound and sight to interact with each other in their underwater world.