The birds' "sunset dance, " in which tens of thousands of black-bellied terns fly in flocks over the ocean at sunset, last year attracted thousands of weekend tourists to the rural township of Beimen.

However, the convergence of large numbers of tourists on the area caused the birds to leave sooner than usual.

Hung Yu-chih, a local guide who is familiar with the birds' migratory habits, said the whiskered terns, which normally would have stayed until April this year, left Tainan at the end of last December.

Last year, more than 10,000 people visited Tainan to watch whiskered terns, said Hung, who also runs a guesthouse in Beimen for bird lovers. "The noisy crowds of visitors seriously disturbed the terns," he said The black-bellied terns -- small marsh terns with a slightly forked tail -- migrate to the coastal areas around Tainan and Chiayi County every winter. During their stay in the wetlands in Beimen near northern Tainan, they usually fly out to sea early in the morning and rest on the oyster racks then return to the wetlands at sunset.

Some bird watchers said that in addition to watching the unique "tornado-like" flight of the birds at sunset, they like to get up early to see them at dawn.

"It was amazing...they were flying so low that it seemed like they were just above our heads, " a bird watcher said, describing his experience.

Hung said he was worried that the whiskered terns, which left early last year, would not return this year. However, they began arriving in September and the numbers are expected to grow to a peak in November, he noted.

Although the first-ever tern-watching activity sponsored last year by the Tainan County government drew lots of tourists to the area, many of them criticized the lack of adequate facilities for bird watching.

This year, the Tainan County government will focus on educating bird watchers rather than on attracting visitors.

Even so, Hung is worried that the birds migratory pattern might be disturbed again.

"I really hope the bird watchers will keep their voices down, " said Hung, "I don't want to see the birds leaving early again." (By Yang Szu-jui and Fanny Liu)