New Function for Bubbles Observed in Hawaiian Humpback Breeding Grounds

Humpback whales are well known for their use of bubbles. One of their most widely documented uses occurs in a feeding context where either an individual or group of humpbacks utilize a variety of bubble-based tactics to net, trap, and herd their prey. 

We report a different use of bubbles by humpbacks in the Hawaiian breeding grounds on multiple occasions between 2000 and 2003 in the Au’au Channel off West Maui, Hawaii. Our research team at Whale Trust filmed a 14-minute interaction between multiple males and one female in which the males circled the female and produced bubbles directed toward the female’s swollen genital region. The female appeared to tolerate and possibly aid in the reception of these bubbles. We have observed similar scenarios on multiple other occasions as well.

These observations are intriguing and reveal a new dimension to male-female interactions on the breeding grounds. There are two primary contexts within which to consider this behavior:

 (1) To maximize mating opportunities – Mating/Estrus Female 

• In the scenario that the female was present to mate and in estrus (a recurring state of sexual receptivity and fertility in many female mammals) this could explain her receptiveness of the males and the males’ attention toward the female. 
• In this case, we could speculate that this interaction may serve a sexual purpose such as helping stimulate the female prior to intercourse or assisting in the release of chemical cues that could signal to the male her reproductive status and readiness to mate. 

(2) To ensure successful birth and calf development – Late Pregnant Female

• In the scenario that the female present was a late pregnant female and about to give birth, this could explain her extended girth, swollen genitals, and even the presence of multiple males around a birthing female. 
• In this case, we could speculate that the bubbles could stimulate the release of hormones, such as oxytocin, known to be vital in the birthing process.
• The pressing question is, if this is the correct case, why are males involved and not females? What is in it for the males?

While interpretation of the use of bubbles in our recording and their exact meaning remains speculative, it does show the complex and wide array of bubble use in humpback whales. Future research aimed at understanding the hormonal state of male and female humpbacks within different social groups and situations on breeding grounds should provide the insight needed to determine the correct context for the behavior patterns described here.