Jackson said most of those studies, done in various penguin colonies around the world, document the negative effects of flipper-banding. She and her co-authors have called for wildlife managers and conservationists in the Cape to rethink the practice.
The problem, Jackson said, is that the bands can impede the penguins' ability to move efficiently. All penguins swim with their flippers, she explained, and the bands can "interfere with the hydrodynamics of the flipper and body."
According to Jackson, there are 18 species of penguin worldwide, and studies so far have shown that at least five speciesKing penguins, Adélie penguins, Little Penguins, Gentoo penguins, and Chinstrap penguinshave suffered negative effects of flipper-banding. As a result, a growing number of researchers in England, France, Germany, Australia, and elsewhere have expressed reservations about flipper bands or stopped using them.
African penguins were not included in the studies published until now. Yet Jackson believes they are likely to be harmed by the banding because their typical body size is midway between the body sizes of the species that have been studied. "Adverse effects have been shown on enough species of widely different body sizes that concerns have been raised about whether the banding of African penguins shows the same trend," Jackson said.
"If banding has an effect," she added, "the magnitude of that effect will vary from species to species depending on the proportion of each species that are banded. In most species, this is small. In African penguins, it's more than 10 percent of the world population."
Comparing groups of banded and non-banded birds from the same colonies over several years, the researchers have looked at how banding may have affected the birds' annual survival, breeding habits, and the time spent on shore and at sea.
The published studies on the effects of flipper bands are based on tests of penguins' oxygen consumption. "This is because, just as in humans, oxygen consumption is an indication of how hard an animal is working," Jackson said.
When penguins dive, she explained, they do so aerobically, taking all their oxygen down with them. "Increasing their oxygen consumption probably reduces time spent underwater, reducing contact time with prey," she said.
Jackson cited studies of captive Adélie penguins, for example, showing that flipper bands increase the average penguin's oxygen consumption by as much as 24 percent, which she calls "a huge amount." Furthermore, she added, published studies have shown that newly banded adult Adélie and King penguins had annual survival rates 28 and 31 percent lower than those of their non-banded cohorts.
Other local scientists disagree strongly with Jackson's assertions. Les Underhill, a professor in the University of Cape Town's Avian Demography Unit, said he and his colleagues fully support the decision to band all the penguins that were rescued and treated after the sinking of the M.V. Treasure.
Underhill said that, unlike Jackson, he and his team have many years of field experience with Cape Town's penguins. He and his colleagues are convinced that their use of banding, which takes into account the African penguins' size and wing-to-body ratio, is not harmful.
"We were aware of all the articles referred to in Jackson's review," he said. "We carefully weighed up the information [the studies] contained against our own personal experience of our own design of flipper bands on our penguins."
Underhill said he and his colleagues have been using the flipper-banding technique for decades in their research on Cape Town's penguins and the only problems they've observed were the result of incorrectly applying the bands.
"Our projects that use flipper banding are directed at conservation issues for the species," he said, "and we would immediately stop flipper-banding if we had any reservations that it was negatively impacting an already vulnerable species."
Explaining why he thinks the use of flipper-banding is required, Underhill said much of what is known about the African penguinsuch as survival rates, the length of generations, and age at first breedingand the threats to its survival has come from information acquired through the technique.
Moreover, he noted, the consensus among researchers who study Spheniscus penguins, which are found in Africa and South America, is that this species doesn't appear to experience the flipper-banding problems that have been seen in other penguin species.
Underhill believes that banding is crucial to provide researchers and conservationists with the kind of detailed information that's needed to help ensure the birds' survival.
At Dyer Island, off the southern coast of South Africa just west of Cape Agulhas, the penguin population has declined much more steeply than in other local colonies, Underhill noted. Little banding has been done in that colony, he added.
"We are kicking ourselves for not having done more banding there over the past 15 years," Underhill said, "because it would help us understand this disturbing phenomenon."
He and other proponents of banding argue that it's still the best way of keeping track of large penguin populations.
Jackson said she recognizes the need to monitor the penguins for research and conservation, especially in light of the African penguins' declining populations.
She also acknowledges that the use of alternative marking devices, which some researchers are calling for, has disadvantages. Using transponders, for example, is more awkward and difficult because the penguins that are being observed must be herded over buried sensors that read the data. The technique also doesn't enable researchers to conduct quick population checks with telescopes and binoculars, as can be done with the banding method.
If local officials refuse to halt the banding program altogether, at least the number of penguins affected should be reduced, Jackson suggested. "Let's only band a small number of birds, and maybe just be more critical of what exactly are our research questions," she said. "We have to be selective."
She also refutes assertions that banding is harmless to the birds, saying: "The basis for that confidence is flawed and not supported by the literature."
Ron Irwin is a co-partner in the Cape Town-based media company Atomic Productions