The bands used to study penguins have been proven to significantly harm the birds.

…the results of a ten-year study of free-ranging king penguins provide convincing evidence that banding is harmful. Banded birds had a markedly lower survival rate, with every major life-history trait affected, and they were more affected by climate variation than birds without bands. As well as raising doubts over marine ecosystem data based on banding, this work has implications for the ethics of animal tagging.

In other words the study data on penguins with bands on their wings is biased by the effects the bands themselves are having on survivability.

One of our major findings is that responses of flipper-banded penguins to climate variability (that is, changes in sea surface temperature and in the Southern Oscillation index) differ from those of non-banded birds.

Some scientists had argued that bands had no impact or that birds would adapt to the bands over time. Instead it now is known that they can not fly as well, they mate less successfully, forage longer and die sooner. The only time they fared the same was when “conditions were so good that penguins might have been able to compensate from the disadvantage of having a flipper-band”. How was a study performed on non-banded penguins to notice the difference? Embedded tags were used instead of bands.

ornithologists have been calling for an end to banding for over a decade

Thus, a solution to risk already existed but the problem had to be proven irrefutably.

How does this band make my wing look?
Photo by Benoît Gineste