Fluke-Up Feeding in Hawaiian Waters

In the past few weeks our office has received numerous calls from concerned citizens about seeing a whale in distress.  The whale observed is spending long periods of time at the surface with its flukes extended above the water’s surface.  Some have conjectured that it is a whale using its tail flukes to sail; others have suggested it is attempting to cool down using its tail as a thermoregulatory device.

We believe a different hypothesis to be true.  The whale with the extended flukes is most likely a female humpback with a newborn calf. The mother is resting while still allowing her calf access to her mammary glands (located near the posterior portion of her body some 6-8 feet from her flukes).  By extending her tail into the air she is able to keep her body relatively close to the surface, allowing her to rest while minimizing dive depths for her young calf.  The calf is then able to nurse at will and expend less energy.

While it is rare to see a female displaying this resting/nursing posture in Hawaii, it is not without precedent.  PWF researchers have observed this feeding behavior in over three dozen female humpback whales off east Australia since 1984.  It appears to be a socially transmitted behavior: initially just a few whales employed this resting and feeding posture, and over the past 20 years we have seen a steady increase of females displaying this behavior. We refer to it as “fluke-up feeding”, or “tail-up feeding”, and once an animal employs this method, they then tend to repeat the behavior with subsequent calves.

The gestation period for humpback whales is between 10 and 12 months, and they have only one calf at a time. A whale has never been seen with two live young, but there are records from the whaling days of a pregnant whale with two fetuses. Humpback whale calves observed in Hawaii are both conceived and born in the Hawaii region. Surprisingly, there is little firsthand evidence of birthing. Scientists have observed newborn calves with their dorsal fin still folded flat against the back and fetal folds along the body. There have also been reports of a placenta being recovered while floating at the surface of the water.

A recent finding by Murdoch University Cetacean Research Unit in West Australia reveals nursing occurs at an average depth of 16 feet.  Most calves nurse throughout the day, and spend 30% of their time nursing in a 24-hour period.  Although most calves nurse opportunistically throughout the day, some females only nurse their calves during the morning hours, and others nurse only at night. Humpback whales have two nipples which, when nursing, will protrude through the mammary slit. To nurse, the calf curls a specially shaped tongue around the nipple and the thick, fatty milk is reflexively squirted into the calf’s mouth. Humpback whale calves drink many gallons of milk per day, which allows them to grow quickly. Newborn humpback whales average 12-14 feet in length and weigh upward of two tons. Lactation continues for 10-11 months and once the calf has weaned, it has little contact with its mother.

There is no need to be alarmed at the sight of a whale with its tail extended for long periods of time: the animal is neither injured nor in harm’s way.  In this case it is a mother who has figured out a novel way to feed her calf while resting and conserving her energetic resources for the long journey back to the northern feeding grounds.

11 thoughts on “Fluke-Up Feeding in Hawaiian Waters

    • Their nipples are located under special slits in their abdomen that are normally inverted which keeps the whale hydrodynamic. When they calf wants milk he or she will prod his or her mother’s belly with their rostrum and the nipples will extrude.

  1. That is so different from what I have read and been told but it makes more sense. Sorry if I was wrong but I can only learn what I am taught.

  2. It would be interesting to drop a GoPro down to see what might be happening. It seems like a good opportunity since the whale is staying put for so long. I know you were getting some great shots like that this winter.

    • Hi Gina, we did attempt underwater filming but were not able to get clear footage. We didn’t want to disturb the whales by getting too close, especially to a mother and calf.

  3. This is a “new” behavior for a Ma’alaea Bay kama’aina like me. I’ve been whale watching with PWF since 2008, going on cruises more than 20 times a seaason, but never saw this one before you published on the blog. As a serious photographer, I tend to shoot whale behaviors I recognize; anything like this one I’ve probably ignored, thinking it was just random whale silliness. I’ll be on the lookout for this behavior on my future cruises. Thanks for this post!

  4. Previously this phenomenon was described as ‘sailing’. Was that just a description because it looked like a sail or was some wind-assisted motion created? Was the latter ever documented and does the new interpretation dismiss that? I’d seen it some years ago below McGregor Point and was confused that the whale was stationary; admittedly it’s somewhat sheltered there. Imagine 45 tons of humpback with its flukes billowing in a 40 knot wind off Sugar beach. It’s brilliant that scientific rigour through observation continually hones our understanding of these enigmatic mammals.

    • Another species of whale, the Southern Right Whale, does have a behavior called sailing. They extend their flukes out of the water for long periods of time and catch the wind, but it appears to be a form of play, not for traveling. The Humpback Whales doing this behavior have all been a mother with a calf, which leads to our belief that this is a feeding strategy.

  5. Pingback: Pod types in Hervey Bay | Pacific Whale Foundation Blog

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