(Inside Science) -- At the end of the Antarctic summer, chinstrap and Adélie penguins abandon their beachside breeding grounds and vanish out to sea. Scientists can track a few of these penguins using instrument tags attached to their bodies. But such tags are expensive and challenging to use, so much about the penguins' winter journeys has remained mysterious. Now, scientists are finally getting a big-picture view of these hidden migrations, using techniques similar to forensic hair analysis.

As penguins forage, distinctive chemical signatures in their food become incorporated into their own tissues. This happens because different forms of the same element, known as isotopes, are present in food and the environment in proportions that vary with location. Researchers have tried to use isotope analysis to map marine bird migrations before, but the results were hard to interpret, according to Michael Polito, a marine biologist at Louisiana State University in Baton Rouge and first author of a paper published today in Biology Letters.

"It was hard to tell if two birds were migrating to the same place but eating different things or if they were migrating to different places but eating the same thing," he wrote in an email to Inside Science. 

In the new study, the researchers examined isotopes of carbon in essential amino acids. These compounds are formed by phytoplankton and then passed unchanged up the food chain, providing a clear signal of where they are from.

First, the researchers placed geolocation tags on 52 penguins before their winter migrations. The following year, they retrieved the tags and collected tail feathers from the penguins, allowing them to compare isotope ratios to migration routes. They also analyzed tail feathers from 60 additional penguins, and inferred where the untagged penguins had traveled.

The insights from the study could help managers conserve penguin populations, according to Polito. He added that other researchers can use the same technique to study the migrations of other species, examining isotopes in everything from seal whiskers to whale baleen.