A new study shows the standard way of tagging penguins for scientific research may dramatically affect their survival and reproduction.
There are now concerns that some data gathered on penguins over the years using the method may now be invalid, the BBC reports.
For decades, scientists have followed penguins by putting bands around their flippers, allowing individual birds to be identified at a distance.
But there have been concerns that the bands might harm the birds by slowing them down as they swim.
The latest study, reported in the journal Nature, confirms it.
Scientists from Strasbourg University in France followed a colony of King Penguins for 10 years and found that birds fitted with bands died younger, started breeding later in the year, took longer to forage for food and overall raised about 40% fewer chicks.
They say continuing to use the tags would in most situations be unethical.
