A bald eagle nest at the old Philadelphia Navy Yard has failed, but birdwatchers are holding out hope that the first pair of bald eagles spotted in the city in more than 200 years will nest again next year. After the nest was spotted in February, state officials began keeping a close eye on the eagles in hopes that they would breed. But birdwatchers and state officials say the eagles haven't been spotted since April. "We believe it is failed and that the birds are gone," said Debbie Beer, a birder who spotted the eagles in February and has been helping the state to monitor them. "I'm hoping that they come back next year and nest again." Beer last spotted the birds on April 5. Dan Brauning, wildlife diversity supervisor for the state Game Commission, said the birds could still be nearby. "I would not expect them to abandon that area," he said. State officials estimate that 20 percent to 30 percent of bald eagle nests fail each year in Pennsylvania. Last year, state officials said they had confirmed more than 100 bald eagle nests in Pennsylvania for the first time in more than a century. State officials have gone back to the Philadelphia nesting site several times, but have found no evidence that the birds returned. The nest's discovery has complicated real estate development plans at the old Navy Yard. The birds are protected by the federal Endangered Species Act, meaning nearby development plans could be altered, delayed or even halted. But the U.S. Fish and Wildlife Service is expected to delist the eagle next month because of how well it has rebounded. Such a move could ease the restrictions on development near bald eagle nests.