These Humpbacks Let Seabirds Bring the Prey

humpbacks let seabirds bring the prey
Jaws wide open, a humpback waits patiently for prey to come to it instead of chasing it.

OFF THE COAST OF CANADA’S VANCOUVER ISLAND, HUMPBACK WHALES have developed a new, low-energy approach to collecting their daily 2,500 kg of delectable edibles like herring. Kicking back and remaining stationary, these humpbacks let seabirds bring the prey to them.

The scientists who have documented the new behavior have termed it “trap-feeding,” after the plant world’s Venus fly traps.

CONVENTIONAL FEEDING TECHNIQUES

Humpbacks (Megaptera novaeangliae) are baleen whales – that is, they earn their livings by gulping in mouthfuls of water rich with small fish prey, expelling the water and dining on the fish.  Mostly, they collect their delicacies through “lunge-feeding,” diving into dense bait balls of small fish prey to gulp in as much a possible.

Humpbacks sometimes engage in a clever technique called “bubble-net feeding,” working with other humpbacks to blow bubbles in circles around schools of herring to group them tightly for easy lunge-feeding.

TRAP-FEEDING: BIRDS BRING THE PREY

The new technique of trap-feeding was first identified by researchers with the Canada-based Marine Education and Research Society. In 2011 they observed a humpback named Conger (humpbacks are identifiable through unique tail fin anatomy) hanging out at the water’s surface for extended periods with his mouth wide open. In this position, MERS says in a blog article, “he spun slowly for about a minute and then used his flippers to push fish toward his mouth!”

Waiting for fish to enter their mouths was something they had never seen humpbacks doing before. In 2011 they identified two humpbacks engaging in trap-feeding. By 2016, the number was 16. Most recently, they have placed the number at more than 20.

THE BIRD/POND FACTOR

Eventually, the scientists realized that the humpbacks were benefiting from the fish-hunting activities of diving birds like auklets and murres, who were engaged in a sort of aerial bubble-net feeding, driving the herring closer together for easier pickings. IN essence, the humpbacks let seabirds bring the prey to them.

In one view, with their mouths half-full, half-out of the water, the herring perceive the open mouths as little ponds in which they can seek refuge.

LESS REWARD BUT LESS ENERGY EXPENDED

Humpback whales letting seabirds bring the prey results in smaller yields of edibles than lunge-feeding, but the MERS researchers note that it’s rewarding because it requires significantly less energy. It will never replace lunge-feeding as standard operating procedure but it serves some whales.

And, trap-feeding thus far is only utilized by this one particular cohort of M. novaeangliae in home grounds off northeastern Vancouver Island. The MERS researchers published their findings last month in the journal Marine Mammal Science.

PRINCIPAL SOURCES: “The innovation and diffusion of “trap‐feeding,” a novel humpback whale foraging strategy,” Marine Mammal Science; “Trap-Feeding” – a new Humpback feeding strategy,” November 2018/“Trap-Feeding” – a new Humpback feeding strategy,” June, 2017, Marine Education and Research Society; “Watch humpback whales trick thousands of fish into becoming dinner,” Science News Feed; “British Columbia Humpbacks Try Out a Mellow New Hunting Strategy,” Hakai Magazine. 

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