Watch Amazon River Dolphins Pee Straight Up Into The Air: They May Be Sending Messages To Their Mates

It’s not unusual for species to have a few tricks up their sleeves that we never knew about. Blue whales can sing low enough to remain undetected by killer whales, tarantulas can run just as fast with six legs as they do with eight, and now research has revealed that Amazon river dolphins (Inia geoffrensis) are peeing straight up into the air.

Scent marking is an important business in the land animal world, it can tell others to keep out, signal all sorts of things to do with mating, and even be something that increases social bonding in chimp society. For aquatic mammals, though, urination is not usually considered a means to communicate. 

We were really shocked because it was something that we have never seen before or heard of from other researchers.

Claryana Araújo-Wang

This makes these observations of wild Amazon river dolphins, also known as botos, between 2014 and 2018 even more unusual. The botos showed unexpected amounts of what the team term “aerial urination”. This involved male botos swimming at the surface of the water on their backs, exposing the penis above the water, and urinating into the air. 

“We first observed this behaviour in 2014 while doing our regular field work. We first saw a male flip his belly up out of the water and expose his penis and then proceeded to urinate into the air. We were really shocked because it was something that we have never seen before or heard of from other researchers,” study author Claryana Araújo-Wang told IFLScience. 

A receiver male is also present in most of these instances and either pursues the stream of urine or stays in the place where the urine makes contact with the water’s surface. 

In total, the team recorded 36 urination events and receiver dolphins were present at 67 percent of them. All of the urination events involved only male dolphins as both the urinator and the receiver. 

Twenty-five of the aerial urination occasions occurred when the botos were in a group setting and 11 occurred with a solo dolphin. This behavior is rarely observed, with only one other photograph of a cetacean species doing this behavior. The team believe, however, that this is a relatively frequent occurrence in young male botos in the Tocantins River. 

“Our study was conducted in a different biome than the Amazon – it’s in the Cerrado (Brazilian Savannah). Thus, this is one of the reasons we just called the animals botos (rather than Amazon River dolphins),” explained Araújo-Wang. 

We believe that aerial urination may have a social function but further understanding of the functions of this behaviour will require more research.

Claryana Araújo-Wang

The time for each of the urination events was typically very short, with an average of around 11 seconds. The team believe that this suggests other factors influence this urination behavior rather than the simple need to pee. 

Instead, the researchers suggest that the behavior is used in social contexts. Amazon river dolphins possess bristles on their rostrums, which may aid in the detection of pheromones or similar chemicals in the urine of the peeing dolphin. 

“We believe that aerial urination may have a social function but further understanding of the functions of 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 possibly mediated through hormones,” finished Araújo-Wang. 

The paper is published in Behavioural Processes.

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