Memory Aids Birds in Migration, Study Finds

James Owen
for National Geographic News
April 29, 2003

Losing your memory? Well, perhaps you should adopt the lifestyle chosen by many birds. New research suggests migratory birds develop excellent long-term memories.

Wings give birds the option of leaving harsh winters behind. Yet migration has its own hazards. Traveling for thousands of miles, across oceans, deserts and mountain ranges, they face the threat of exhaustion, starvation, or simply getting lost.

Despite this, an estimated 50 billion birds manage to return to the same wintering and breeding sites every year. Some, like the Arctic tern, have covered 10,000 kilometers (6,214 miles) or more.

Their safe arrival depends on accurate navigation. There are various ways in which birds accomplish this.

Ornithologists have found birds can set their compass to the sun, moon, or stars. They are also guided by the Earth's magnetic field. Some even home in on their destination using a finely tuned sense of smell. Such skills are thought to be innate—part of their genetic makeup.

Increasingly, there is evidence that these navigational aids are replaced in older birds by more complex systems. These depend on seasoned migrants being able to learn from experience.

New research, published this week in the Proceedings of the National Academy of Sciences, suggests birds do this by improving their long-term memory to map migration routes.

The study was carried out by Claudia Mettke-Hofmann and Eberhard Gwinner at the Max Planck Research Centre for Ornithology in Andechs, Germany.

They found that migratory garden warblers (Sylvia borin) are able to memorize and remember a particular feeding site for at least a year. Its close relative, the Sardinian warbler (Sylvia melanocephala momus), which is nonmigratory, wasn't able to retain this information for more than two weeks.

Memory Tests

A total of 131 garden and Sardinian warbler chicks were collected from nests—from Germany and Israel respectively—and kept in large aviaries. Specially constructed "experimental rooms" were also made to test the memory of the two species.

The study began by allowing each bird into an experimental room for 8.5 hours. The rooms included two compartments, each containing different artificial vegetation to represent two habitat types. Both compartments contained food bowls but these were filled in only one of them—so representing high- and low-quality habitats.

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