Wildlife

Angry Birds? Seagulls Implicated in Baby-Whale Deaths

At least 626 right whale calves died off Península Valdés off the coast of Argentina between 2003 and 2014, and seagulls may have played a role in their deaths, a new study suggests.

While you might think of seagulls as mere pests — squawking masses of feathers that loom over the beach, waiting for dropped potato chips — these birds pose a serious threat to several species of animals, including the southern right whale (Eubalaena australis).

Gull harassment of right whales off Argentina's Península Valdés has been observed since the 1970s. That's when kelp gulls (Larus dominicanus) were first seen pecking the skin and blubber off the backs of adult female whales that use this sheltered spot off Argentina's Atlantic coast as a calving ground. Since then, researchers from universities and conservation institutions in Argentina and the United States have monitored the gulls' behaviour. Their most recent observations of the gulls' continued harassment of right whales — and this behaviour’s potential link to soaring calf deaths — were published last month (Oct. 21) in the journal PLOS ONE.

The kelp gulls' feisty feeding behaviour has gotten progressively worse since it was first documented.

However, the relationship between gulls and right whales started innocently enough. The birds would hover over the giant mammals as they breached, or jumped out of the water to breathe. When breaching, some of the whale's dead skin is sloughed off, floating to the surface and providing a tasty snack for gulls, she said. But several decades ago, the gulls adapted this behaviour to include pecking at the whales themselves as they breached.

A graduate student [Peter Thomas] observing the whales noticed that the seagulls had begun to land on top of the mothers and peck at them, making a hole. Then, in subsequent attacks throughout the season, they'd make the hole larger.

These holes, or lesions, grew to be large ovals, sometimes stretching all the way down the centre of the whales' giant backs. (Female right whales grow to be about 49 feet, or 15 meters, long, from head to tail.) But starting in the 1990s, something changed: Fed-up mother whales started defending themselves against the birds' attacks by keeping their backs underwater when they breached. This was good news for mother right whales, but bad news for their babies. The zero- to three-month-old calves don't know how to keep their backs underwater. Their backs are too small to arch, and now, the gulls' primary targets are the newborn calves.

In the 1980s, when mother whales were still the gulls' primary targets, the average right whale calf had just two small lesions on its back. But by the 2000s, the average number of lesions on the calves' backs had grown to 20. One calf that had been repeatedly pecked at by the birds had lesions covering 19 percent of its back, the study found.

The increase in lesions on baby whales in recent years is linked not only to a decrease in lesions on mother whales but also to an increase in the frequency of gull attacks, according to the study, which states that such attacks have increased "dramatically" over the past three decades. Mother-calf pairs may spend 20 percent of daylight hours dealing with such attacks

The study authors also pointed to recent research about the horrid eating habits of kelp gulls in another part of the world. In Namibia, seagulls peck out the eyes of juvenile Cape fur seals, making them highly vulnerable to repeat attacks in which the gulls consume the baby seals' skin and blubber. This research suggests that attacks by kelp gulls could potentially lead to the deaths of "young marine mammals" that can't easily recover from injuries caused by the gulls.

Whether the deaths of the young whales can be fully attributed to the behaviour of the gulls remains uncertain, however the constant stress caused by the gulls and the gaping wounds they inflict might also inhibit a calf's ability to fend off other threats, like dehydration, parasitic infection or even hunger.

Japan whaling fleet sets to sea for hunt

Japan's whaling fleet set out for the Antarctic on Tuesday to resume a hunt for the mammals after a year-long hiatus, prompting criticism from Australia as well as key ally, the United States.

Japan aims to take more than 300 whales before the hunt ends next year and nearly 4,000 over the next 12 years as part of a scientific programme to research the whales.

The International Court of Justice (ICJ) ruled last year that Japan's whaling in the Southern Ocean should stop and an International Whaling Commission (IWC) panel said in April that Japan had yet to demonstrate a need for killing whales.

But Tokyo retooled its plan for the 2015/16 season to cut the number of minke whales it intends to take to 333, down by two-thirds from previous hunts.

Japan, which has long maintained that most whale species are not endangered and that eating whale is part of its food culture, began what it calls "scientific whaling" in 1987, a year after an international whaling moratorium took effect.

The meat ends up on store shelves, although most Japanese no longer eat it.