Why do whales behave like they do in Hawaii?
The answer lies, ultimately, in the female humpback whale’s biology. During the winter, some female humpbacks come into relatively brief periods of sexual receptivity called estrus. Humpback whales are seasonally polyestrus, undergoing several estrus cycles during a single winter season until successfully pregnant.
But that is about 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. But what about females with a male escort or companion? Is he guarding her pre-estrus, during estrus, or after conception?
Whale Trust Maui researchers are working with others (see our students) to explore whether or not steroid hormones (estrogen, progesterone) stored in a whale’s blubber layer will one day help us to detect pregnancy or even estrus in free-ranging humpback whales.
Exploring Social Behavior in Whales
Female humpback behavior patterns in Hawaii fall into two realms: mating and calving (birth, newborn care). But do these seemingly different reproductive objectives lead to differences in how a female responds to and interacts with a male?
In a recent study, we predicted that female humpbacks would behave and interact with males differently based on their reproductive status (that is, whether or not they had a newborn calf).
To test this hypothesis, we tracked and followed females both with and without a calf on the Hawaiian breeding grounds to see what a day in the life of a female humpback was like. We recorded their movements, behaviors, social interactions, measured their body size and that of their male companion, and played back sounds produced by males in multiple-male, surface active groups to see whether or not females responded differently to males based on their reproductive status.
Our results suggest that female reproductive status is an important consideration in understanding and interpreting female behavior on the breeding grounds, especially around males.