Some previous studies concluded the metal bands, like the one on the penguin at the centre of this photo, had no long-term ill effects on the birds. (Benoit Gineste/Universite de Strasbourg)

For decades, flipper banding has been used to tag and monitor penguin populations, but the findings of a 10-year study could be the death-knell of the practice.

French and Norwegian researchers who studied 50 banded and 50 non-banded free-roaming king penguins on Antarctica's Possession Island say the practice impairs reproduction and reduces life-expectancy.

Some previous studies concluded the metal bands had no long-term ill effects on the birds. The new study, published Thursday in the journal Nature, disputes the earlier assumption that penguins adapted to bands within a year.

The researchers, led by Claire Saraux of France's Université de Strasbourg, say that over the course of the study, flipper-banded penguins produced 39 per cent fewer chicks and had a 16 per cent lower survival rate.

During the 10-year study, 80 per cent of the banded birds died, while only 64 per cent of the unbanded birds died, demonstrating a dramatically reduced life expectancy for those with bands.

Andre Chiaradia, penguin biologist at the Phillip Island Nature Park in Australia, says the impressive thing about the research is that it was the first time a penguin population was studied over such a long period.

This allowed other factors to be equalized, and a valid comparison to be made between the banded and unbanded birds, he says.

"The thing about this study is that they could look over time", he said. "And they could follow the same individual over 10 years and say OK, this is the effect of the band. What comes up quite clearly when you filter out all these factors is that birds with the bands are underperforming."

Drag effect

Penguins power their swimming exclusively with their flippers, and there was increasing concern that the hydrodynamic drag created by the bands would severely hamper the birds in the long run.

"Penguins are this perfectly streamlined machine for diving," Chiaradia said. "They have almost no turbulence, an amazing hydrodynamic structure. So, even a flipper band is going to have a huge drag effect."

Indeed, a study of captive Adelie penguins published in the journal Functional Ecology in 2002 found banded birds expended 24 per cent more energy than their unbanded colleagues.

Chiaradia says that when food was plentiful, the extra energy required by a band didn't make a difference to a bird's ability to feed itself and its chicks. But when prey was not so abundant, the extra work needed to find food did make a difference.

"If the conditions get really tough and you go into survival mode, you have to search longer for your food, you have to work really hard," he said.

"You have to intensify your effort, and you have this handicap. This is going to affect your performance. You're not going to perform as well as the birds without the bands."

Studies in the 1970s on birds both in zoos and in the wild also found that bands often caused severe injury to flippers. Many researchers abandoned the practice during the 1980s. These days most research programs use microchips or other alternatives, but some banding continues.

"In the past, researchers thought the birds would get used to [the band] and compensate for it," Chiaradia says.

"But this study is the nail in the coffin for banding, because this is proving that there is a long-term effect. That's very impressive."