Dozens of sick or injured migratory birds are being nursed back to health in Shunyi district after being handed over by concerned residents.

Beijing Wild Animal Aid and Breeding Center received 71 birds in March and April, said staff worker Shi Yang, who explained most were either too hungry to fly or had struck windows of high-rise apartment blocks.

The number is not unusual for the spring, when many species return to the capital after the winter. A starving swan that was found on the ground in Daxing district on April 18 has recovered but will have to wait until the autumn to rejoin its family, said Shi.

"We release the birds as soon as possible. If they stay in the center for a long time, wild birds usually can't find their family or lose their survival instincts," he added.

Since being set up in late 2005, the 16-hectare animal shelter has helped more than 20,000 wild animals, 90 percent of which were birds.

Every year roughly 1,000 birds are handed over by residents, said Shi, who added: "The calls will increase in the summer when young birds start to leave the nest and learn how to fly."