There’s nothing quite like a day at the beach with a few thousand penguins.

Every year about this time, penguins congregate in the far southern hemisphere to build nests and raise families. You’ll also find biologists there, wrapping tags on the penguins’ flippers so they can follow those birds for life.

But some scientists now say tagging is too harmful because it undercuts a penguins’ most important skill: swimming.

I was lucky enough to watch penguins swimming from a cliff overlooking an Argentinean beach where thousands of Magellanic penguins had gathered. Like awkward mannequins, they waddled down to the water. But when they dived in, they were transformed into black and white torpedoes.

Rory Wilson has watched penguins for 30 years.

“Even people who work on penguins don’t appreciate how stunning they are underwater, how maneuverable and how fast,” he says. “You know, they are just — it’s hard to describe it.”

Slowing Down The Penguins

Wilson and other scientists have shown that penguins have a very, very low coefficient of drag, which is a mathematical measure of how well a body moves through air or water.

“If you were shaped like a penguin,” Wilson says, “you could kick off the side of a swimming pool and just go yards and yards and yards.” But Wilson and other biologists say some tags seemed to increase drag and slow down penguins.

These tags can be plastic, aluminum or other kinds of metal, and they are usually about an inch wide, a few inches long and wrap around the narrow base of a flipper. It’s hard to imagine they’d slow down a penguin, but Wilson, from the Swansea University in Great Britain, says they do.

“Think of it like this: If you had a speedboat or something and then you took one of your bands and then you stuck it to a propeller, would you expect the boat to perform in the same way?” he says.

Effects On Survival And Breeding

And now a research team from the University of Strasbourg in France has evidence to back up what Wilson has seen.

The French team put traditional metal bands on fifty King penguins that live near Antarctica. Fifty others had much smaller radio-frequency transponders. Ten years later, the survival rate for banded birds was 16 percent below the unbanded birds.

Yvon Le Maho, the chief biologist, says at first there was little effect. Then during the first 4.5 years, survival rates for the banded birds dropped about 30 percent below the unbanded birds.

“In other words, only the super-athletes are surviving,” Le Maho says.

The numbers were worse for breeding — banded birds produced 39 percent fewer chicks.

Le Maho found that banded birds took longer to forage for food in the ocean and they were slower to get to breeding sites in the spring. That meant adults had less time to raise their chicks before heading off for lengthy foraging trips in the winter.

“At some time, they have to leave while their chick is too young and too poor in [reserves of] body fuels to withstand the winter,” Le Maho says.

‘All Bands Are Not Created Equal’

The study appears in the journal Nature, but the verdict on tags is by no means clear. Other scientists say they’ve got different results. Among the world’s leading penguin experts is Dee Boersma, at the University of Washington.

The French study, she says, “shows that the bands that they used on King penguins harmed the King penguins — I have no doubt about that. But all bands are not created equal. It depends on what material that they are made of, it depends on how they are shaped, it depends on how they are fitted to the individual penguin. It depends on what penguin species it is.”

Boersma has also studied bands on Magellanic penguins she’s followed for some 30 years in Argentina. Aluminum bands were harmful, but stainless steel ones were fine. She says eliminating all tags would be throwing the baby out with the bath water.

“In almost all cases, whenever we do science, we would like to do no harm,” she says. “But in fact we do have to do some harm if we want to follow individuals.”

Following individual penguins is increasingly important — they are sentinel species that are likely to show the first effects of climate change. And biologists agree they don’t want to blame climate change for some effect that’s really caused by a bad flipper band. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.