Penguin Tags Are a Drag -- Can Rubber Improve Them?
for National Geographic News
|September 29, 2004|
At a glance, it is nearly impossible to identify an individual penguin
in a colony of several thousand. That's a serious problem for
researchers who want to identify and track individual birds as part of
their efforts to protect them.
To overcome the problem, many researchers attach stainless steel identification tags to the penguins' flippers (wings), but some long-term studies suggest these tags rub at the birds' insulating feathers and slow the birds down as they swim through the water.
"There's quite a bit of controversy about it," said Peter Barham, a polymer physicist with Bristol University in the United Kingdom.
Barham, who is not a biologist by training but passionate about penguins, is designing a new identification tag made out of silicone rubber. He hopes the new tags will be less harmful to the birds.
Dee Boersma, a conservation biologist and penguin expert at the University of Washington in Seattle, said that determining whether the new silicone rubber tags are an improvement will require several years of tests.
"It's always a good idea to develop new bands, but the real question is will these new bands be better?" she said. "We won't know until someone tests them and sees."
The new tags are designed to be flexible enough to prevent wear on the birds' feathers yet fit snuggly around the wing, thus reducing any tag drag that may slow the birds as they swim.
The first generation of Barham's silicone rubber tags fit like an airfoil on the flipper but proved too cumbersome when tested on wild penguins in South Africa. A second-generation prototype, designed more like a ring, is currently being developed.
Preliminary results from tests of the new prototype on captive penguins suggest an improvement over conventional stainless steel tags. She says but "whether it will work in practice has yet to be seen," Barham said.
Boersma is currently preparing a manuscript describing results from a ten-year study on a variety of tagging techniques, researchers will need at least five years of data before any conclusions can be made concerning the efficiency of the silicone rubber tags.
Sue Jackson studies ecological and evolutionary physiology at the University of Stellenbosch in Matieland, South Africa. In 2002 she published a review paper on the impact of tags on penguins. She is concerned the new tags simply perpetuate a "bad system."
According to Jackson, any external tag attached to a flipper will cause some degree of hydrodynamic drag. And any degree of hydrodynamic drag is unacceptable, she said.
"Even if the band shape looks streamlined, it is not streamlined relative to the shape of the penguin, and that turns out to be very important for how much energy they use when they swim," she said.
Jackson said a 5 percent increase in the amount of energy it takes for a penguin to swim after and capture its prey is equivalent to a 5 percent rise in the cost of food at the grocery store.
Such an increase impacts how much food the penguin eats, how long it lives, and the survival of its offspringthe very type of demographic data the tags are designed to collect.
According to Boersma, all tags have a cost, but researchers "have to have some way to identify individuals if you are interested in demographics, or interested in differences in individuals over their lifetimes or age groups."
Barham acknowledges that some researchers "are totally opposed to external marking of birds." As an alternative, a member of his lab at Bristol University is developing computer software to identify African penguins by unique feather patterns on their chests.
The problem with such a system, according to Boersma, is the labor and time cost of taking a picture of an individual and then running the image through a database to search for a match. The system is also several years from being fully developed.
"There's no doubt we can learn individual penguins, but having 200,000 pairs in a colony makes it difficult," she said.
Jackson encourages the research community to more widely adopt an alternative: the use of so-called transponder tags that are implanted under the skin. Whenever the penguin walks past a receiver, the penguin's identity is revealed.
However, scientists say such a system is more expensive than the plastic or stainless steel tags. Also, transponder-tagged birds cannot be identified without a receiver, and the equipment requires considerable maintenance. The transponder tags also have high failure rates and can cause infections.
"They do, however, yield data that are not flawed by the substantial negative effects on the very parameters that flipper bands are used to study: annual adult and juvenile survival at sea, and breeding success," Jackson said.
According to Boersma, no tagging technique is ever going to be perfect for all situations and all species of penguins. Another question researchers need to be asking, she said, is, "When do you need to mark an individual and when don't you?"
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