MATING BEHAVIOR

MATING BEHAVIOR

Knowledge of female humpback behavior in a mating context may be the least-known aspect of this species’ behavior today

Humpback whales have never been observed mating – either in Hawaii or anywhere else in the world. This suggests that mating may happen out of sight and fairly quickly.  But by traveling to Hawaii, female humpback whales make themselves accessible to sexually active male whales – a lot of them! If mating is not an objective, then they have definitely chosen an interesting place to spend the winter. 

How do male and female humpbacks find, select, and obtain mates? Does she simply swim onto the breeding grounds and make herself available? Does she behave in a way that encourages male competition? Does she actively choose males with specific attributes?

What We (Think we) Know ABOUT FEMALE MATING BEHAVIOR 

During the winter, mature female humpbacks come into relatively brief periods of sexual receptivity called estrus. Humpback whales are seasonally polyestrous, undergoing several estrus cycles during a single winter season until successfully pregnant. 

But that is all we know about estrus cycles in humpback whales. We presume that females are in or near estrus when they are found in multiple male or surface-active groups where males actively compete with one another. But what about females with a male escort or companion? Is he guarding her pre-estrus, during estrus, or after conception? Why are females with calves most often found with a male escort? 

Understanding the reproductive cycle of females is key to answering these basic questions. Whale Trust’s current research is addressing this gap in our current understanding.

WHAT IS COURTSHIP IN HUMPBACK WHALES? 

Although we do not know much about what defines courtship, we can gain some insight into the different mating strategies by observing how males and females interact. With a reported sex ratio of 1.82 males to every one female on humpback breeding grounds, female humpbacks are in high demand during the breeding season.³ 

Bubbles: A Form of Courtship?

The use of bubbles in humpbacks appears to serve multiple purposes on the breeding grounds. We have observed occasions where male humpbacks will produce bubbles directed toward a female’s swollen genital region. The female appeared to tolerate and possibly aid in the reception of these bubbles. These observations are intriguing and reveal a new dimension to male-female interactions. If the female was present to mate and in estrus, this could explain her receptiveness to 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.

Male-Female Breath-holding Pairs: Is this when mating occurs? 

One of the most common groups on the Hawaiian breeding grounds are resting pairs of whales. These pairs have earned the nickname “breath-holders” due to their relatively long downtimes (20-25 minutes on average). Using genetics, Whale Trust research found that these pairs are male-female pairs, and that they are often together at the beginning or ending of “competitive groups”. 

Males in these groups often “guard” the female and try to keep other males at bay. The question we are trying to answer through our current studies focused on reproductive hormones is whether he is guarding her pre-estrus, during estrus, or after conception. Understanding this missing link will provide key insights into humpback mating behavior on the breeding grounds. 

Surface Active or Competitive Groups: Is this WHERE mating occurs? 

Breath-holding pairs eventually attract the attention of additional males, changing the group composition to a more competitive, surface active group. The heightened male attention and aggressiveness observed between males in these groups led researchers to presume the female is in estrus. While intuitively this makes sense, there has yet to be any observation of mating in these groups. By collecting tissue samples of both males and females in these groups, we hope to shed some light on the reproductive state of females in these groups. 

Females with Calves 

Despite having just given birth and a commonly observed 2-3 year reproductive cycle, at least some mothers are mate shortly after giving birth. The percentage of mothers that successfully conceive is unknown. Whaling data indicated that a small percentage of mothers were able to successfully conceive after giving birth.⁴ Observations of females in Alaska have shown that one well-known female (Flame) gave birth to four calves in four subsequent years. 

Without the knowledge of the female reproductive cycle, we can only speculate what these interactions mean in terms of mating and courtship.

Whale Trust’s research is working to address these questions and more! We are currently focused on learning about female reproductive cycles by examining tissue samples taken from humpbacks on the breeding grounds. These tissue samples contain reproductive hormones that we can extract and measure to provide insight into the female’s reproductive condition. You can explore our most recent projects on our Current Research page.

References

1. Jones, Meagan E. 2010. Female Humpback Whale (Megaptera novaeangliae) Reproductive Class and Male-Female Interactions during the Breeding Season. Antioch University, New England. 184 pp. (Download PDF)
2. Jones, M.E., Nicklin, C.P., and Darling, J.D. 2022. Female Humpback (Megaptera novaeangliae) Whale Positions Genital-Mammary Area to Intercept Bubbles Emitted by Males on the Hawaiian Breeding Grounds. Aquatic Mammals. 48(6), 617-620. (Download PDF)
3. Herman, L. M., A. A. Pack, K. Rose, A. Craig, E. Y. K. Herman, S. Hakala, and A. Milette. 2011. Resightings of humpback whales in Hawaiian waters over spans of 10–32 years: Site fidelity, sex ratios, calving rates, female demographics, and the dynamics of social and behavioral roles of individuals. Marine Mammal Science 27:736–768.
4. Chittleborough, R. G. (1958). The breeding cycle of the female humpback whale, Megaptera nodosa (Bonnaterre). Aust. J. Mar. Freshw. Res., 9, 1 -18.