"With only around 1,200 pairs confined to this small island in the Indian Ocean, the Christmas Island frigate bird is one of the worlds most threatened seabirds," said Ed Parnell, spokesman for Birdlife International. "This new satellite tracking data will add enormously to our knowledge of the species."

James said the distance Lydia traveled raises some serious questions about efforts to stem the decline of the birds, whose numbers have fallen by 10 percent over the past 20 years.

"We're surprised she would have spent that long away from her nest when she had a chick," he said. "That begs the question: Why does she need to go that far? It raises the suspicion that fish resources around Christmas Island are not currently adequate. That might explain the slow and gradual decline of the bird."

James and Birdlife officials said Lydia's route also raised concerns, since it covered industrial areas, mining sites and waters popular with commercial fishing fleets.

"It is tragically ironic that while Lydia nests on one the world's most remote and pristine islands, she makes her living in some of the most degraded seas on the planet," James said. "Fishing pressure is huge and marine pollution is severe."