The number of cygnets staying in Shanghai for the winter has more than doubled from a year ago to 478, the Oriental Morning Post reported Thursday.

More of the protected migratory birds have been spending the season in Shanghai in recent years. The Shanghai Wildlife Conservation Management Station reported that 201 cygnets wintered in Shanghai in 2011, the highest number in about a decade, according to the Shanghai Morning Post.

Despite the increase, Shanghai's cygnet population remains a far cry from where it was in past decades, according to Yuan Xiao, an expert with the wildlife station.

"In the 1990s, there were more than 3,000 cygnets wintering in Shanghai," he told the Global Times.

The population has collapsed as cygnet habitats have shrunk in the city, Yuan said. The trend is part of a broader drop in the number of migratory birds passing through the city. According to a wildlife station investigation from last year, the number of migratory birds wintering in Shanghai, including cygnets, plunged 25 percent from 2006 to 2011 due to a shrinking habitat, according to the Oriental Morning Post.

For example, about 3.3 square kilometers of intertidal mud flats along the coast of Nanhui in Pudong New Area - which had been a habitat for migratory birds - was re-purposed into farmland last year, according to a report in the News Times.

The rise in the cygnet population over the last two years doesn't prove that the local environment has improved, Yuan said.

"The number doesn't mean that Shanghai has become a friendlier place for migratory birds," Yuan said.