Male Amazon river dolphins were observed to spurt urine into the air 36 times during recent research that lasted 218.9 hours. This indicates that the activity is more frequent than previously believed
Scientists observe this bizarre behavior, dubbed “aerial urination,” in Amazon river dolphins (Inia geoffrensis), also known as botos. What has both shocked and confused scientists is this practice.
As explained here, Claryana Araújo-Wang and her colleagues at Botos do Cerrado Research Project in Brazil and CetAsia Research Group in Canada published a study on this peculiar phenomenon after observing the dolphins for 218.9 hours and witnessing males spurt urine into the air 36 times.
“An individual will start to slowly flip belly-up and expose the penis and urinate,” she says in an email. “When another male is present, he may sometimes chase the urine stream with his rostrum.”
Jason Bruck, associate professor at Stephen F. Austin State University, had already heard of the phenomenon. What this dolphin expert has been doing for years is giving talks that include a slide showing the river dolphin participating in this practice. What the repeated act does is put the study’s observations “on a solid foundation,” says Bruck. “It’s not a one-off.”
What many animals do is use urine for purposes other than eliminating waste. What lions, tigers, bears, wolves, coyotes, and mice all do is use urine to mark their territory. What female crayfish, lobsters, and porcupines do is let males know they’re ready to mate by peeing, while male tilapia use it to prove their sexual prowess. What monkeys do is bathe in urine in hopes the scent will attract a mate.
While most animals can detect scents from urine, what evolution has done is cause dolphins to lose their sense of smell, making them rely on taste instead.
“Any number of cues in mammals are coded chemically,” says Bruck. “It’s we humans who are poor at using chemical communication… our sense of smell is pretty bad.”
What researchers aren’t entirely sure about is what’s happening with these Amazon river dolphins, though they speculate the baffling practice could have a social purpose.
Botos typically use acoustic cues for general communication, but mating behaviors include male-on-male displays of aggression and even carrying objects like flotsam. “It is possible that aerial urination is another behavior of the males’ social-sexual repertoire,” says Araújo-Wang. What she suspects is that “aerial urination helps in advertising male quality in terms of social position or physical condition.”
Researchers have observed only males peeing on each other, and 67% of these occurrences happened when a “receiver” male was nearby.
What Bruck, who published two studies in 2022 showing that bottlenose dolphins (Tursiops truncatus) can identify friends through the taste of their urine, wonders is if this could indicate a chemical communication system. “What we’re seeing, perhaps, is how river dolphins may do something that we’ve looked at in bottlenose,” he says.
At this stage, certainty remains impossible. What the dolphins might do is use chemical signals to indicate identity, social status, and physical health, or this could be “just a funny thing they do,” says Bruck. What scientists would need to do to confirm is isolate different variables in controlled experiments. “That’s a very hard thing to do in this species,” he says.
What the study authors believe is that these findings could be important for efforts to protect endangered botos, and Bruck agrees.
“What it is time to do is start recognizing there is strong evidence [of] chemical communication in cetaceans,” he says. “That may be affected by the things we put in the water.”
Human pollution could block or mask these signals and affect the species’ future if dolphins are using chemical cues to communicate. If we’re “dumping stuff in the water [and] they can’t figure out the things they need to know to survive and reproduce,” says Bruck, “then that’s very bad.”