Bar codes pin down penguins

How do you tell one penguin from another? Though penguins do not find it much of a problem, scientists have always found it tricky. But now the answer seems to be at hand: bar codes, like those for supermarket goods, stuck to their beaks.

The codes, which have enough stripes to cater for flocks of up to 1,000 birds, were tested by British Antarctic Survey (BAS) researchers earlier this year. "We have always had other means of telling them apart," said Andrew Clarke, head of marine-life sciences at the BAS. "We could put tags on their legs or flippers. But that means you have to catch them to read it back. And if they have guano or something on their legs it makes them very hard to read."

The bar codes, by contrast, can be read by photographic equipment from up to 400m, making life far simpler for scientists studying the birds' breeding and feeding habits. "The polar regions are primary indicators of global climate changes and differences in penguins' behaviour can be a good way to measure them," said a BAS spokeswoman.

Any penguin that attracts a bar code may be stuck with it for some time: the stickers are attached with epoxy resin. Dr Clarke said: "It works very well in cold temperatures and in the sea. We stuck labels to some limpets before using the same stuff, expecting it only to last a couple of months. They were still there after two years."

Looking like something out of a supermarket is not the only indignity the penguins go through. To estimate how well they are feeding, scientists have installed a "weigh-bridge" between the sea and the penguins' nesting site. They usually take a standard route between the two sites, so getting them to pass over a weighing system is only a matter of "tweaking" their path, Dr Clark said.

"Using that, you can measure their weight and check their bar code at the same time. Understanding how well they feed is important to understanding how the population behaves, because that sort of information is hard to get."