Seagulls Attacking Whales Off Argentina

Kelly Hearn in Buenos Aires
for National Geographic News

December 4, 2006

In the frigid waters off Argentina's southern Valdés Peninsula, the
southern right whale is under attack from an odd-sounding predator: the
seemingly docile seagull.

Uncovered garbage dumps and waste from fish-processing operations have fueled a spike in the number of kelp gulls in the region's coastal towns (Argentina map).

Experts say the birds, which nest near the prime breeding waters for the endangered whales, are causing a peck of problems.

"The gulls are landing on the whales and pecking through their skin to feed on the blubber, which is an important source of calories," says biologist Marcelo Bertellotti of Argentina's Patagonia University.

"This is causing lesions and impacting whale behavior." The kelp gull is a flexible eater that hunts insects and scavenges through trash heaps.

But it is especially fond of whale blubber, normally dining on dead animals or snatching up blubber dislodged by the whales' trademark somersaults, Bertellotti says.

However, some aggressive gulls go further for a meal.

"Some individuals have developed the capacity to take skin and blubber from live whales," he said.

Mothers and Calves Attacked

Researchers don't know what causes some the birds to get aggressive, but they note that the attacks often create wounds and, in some cases, transmit viruses and bacteria.

Bertellotti and Fundación Vida Silvestre Argentina (FVSA), an organization associated with the World Wildlife Federation, say the kelp gulls' pesky gouges force whales to dive and flee.

That interrupts crucial rest and feeding periods, forcing the animals to expend energy normally used to make fat layers for long migrations or to produce mother's milk.

Alejandro Arias, the species coordinator of FVSA's marine program, says 80 percent of the gull attacks are aimed at female whales and calves.

Southern right whale mothers spend a quarter of their day fleeing seagull attacks, according to FVSA.

But Bertellotti, the Patagonia University biologist, says it is unlikely that female blubber tastes better.

"The attacks are directed at all whales," he said. "The mothers receive more attacks because they pass more time along the surface when they are with their claves."

"The calves are the most affected because of [their softer skin] during first days of life and because they spend more time at the surface," he added.

The whales are significantly outnumbered by the gulls.

About 10,000 southern right whales use the coastal waters off Argentina , Australia, and South Africa as nursery areas, according to FVSA.

Meanwhile, 75,000 reproductive kelp gull couples occupy six main colonies along the Argentine coast, the group says.

(See Argentina photos, maps, more.)

Attacks on the Rise

British researchers first observed the attacks in 1969.

The number of aggressive birds has grown as the gull population has increased thanks to an abundance of human-supplied food sources in coastal towns.

Though the number of attacks has gone up, the attacks occur sporadically.

"Without a doubt, the attacks are not constant," Bertellotti said. "There are months when they are more frequent, and at other times they are nonexistent."

Arrias says FVSA is working to raise local awareness.

"In some places we are seeing a decline or stabilization of gull populations thanks to some changes," said Arrias, noting that at least one community, Puerto Piramide, has covered its landfills.

His group is also studying how the attacks will affect the region's whale-watching industry.

Scientists also want to know if the attacks are changing the whale's regional distribution patterns.

"I don't think the attacks are producing redistribution," Bertellotti said.

But the biologist plans to outfit some whales with specialized "suction caps."

The tracking devices will help chart the whales' movements to better understand the effects of the seagull attacks and other disturbances, he says.

Fellow Patagonia Univeristy biologist Gustavo Pagnoni has also studied the problem.

He notes that the growing gull population can put a territorial squeeze on some bird species.

But Pagnoni maintains that not all human development along the coast has prompted negative impacts.

The same human-supplied free lunch that boosts kelp gull numbers also draws other birds that increase local species diversity, he says.

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