A groundbreaking study published in the February 2025 edition of Behavioural Processes has shed light on a peculiar behavior exhibited by male botos, or Amazon river dolphins. Conducted by researchers Claryana Araújo-Wang, Mauricio Cantor, and John Y. Wang, the study reveals a captivating aspect of cetacean behavior: aerial urination. The research, which spanned from September 2014 to March 2018, meticulously documented 36 instances of this rare phenomenon, exclusively involving wild male botos in Brazil's Tocantins River.
The team first encountered this behavior in 2014 during their routine fieldwork. Araújo-Wang noted that they "observed this behavior in 2014 while doing our regular field work." By March 2016, they had captured footage of a male boto urinating into the air, a scene of great intrigue to the scientific community. "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," Araújo-Wang recounted. The duration of these urination events averaged around 11 seconds, leading researchers to hypothesize that the act serves a social purpose beyond mere biological necessity.
The study offers insights into the social dynamics of male botos, drawing parallels with similar behaviors observed in other species. Araújo-Wang stated, "We were really shocked because it was something that we have never seen before or heard of from other researchers." In their detailed observations, the researchers described how a boto "starts with a boto slowly positioning itself upside down, exposing its penis above water, and ejecting a stream of urine into the air."
The presence of a "receiver" male appears significant in these interactions. As described by the research team, "When a ‘receiver’ male is present, it either approaches the urine stream with its rostrum (sometimes pursuing it) or stays where the stream contacts the water." This suggests a potential social signaling mechanism akin to behaviors seen in chimpanzees, where urination can be socially contagious.
Although the researchers remain uncertain about the precise function of this behavior, they believe it may be intricately linked to social interaction among male botos. Their findings highlight an aspect of cetacean behavior previously undocumented, adding a new dimension to our understanding of these unique creatures.
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