The rare Laysan ducks at Midway Atoll National Wildlife Refuge had a successful breeding season, adding 56 youngsters to their population.

U.S. Geological Survey biologists report the duck population at Midway now stands at 104, which is encouraging since the endangered birds were re-introduced there only two years ago as part of an experimental conservation program.

Beginning in 2004, 42 ducks were brought to the refuge from Laysan Island to increase its geographic distribution and reduce the risk of extinction from disease, natural disaster or other causes.

The Laysan duck (Anas laysanesis), also known as the Laysan teal, is considered the rarest native waterfowl in the United States, and lives only within the Northwestern Hawaiian Islands Marine National Monument, established June 15. The birds were once widespread across the Hawaiian Islands, but by 1860, they were gone from all but Laysan Island.

The ducks do not migrate, so they were taken by ship to the three-island Midway Atoll, where scientists and volunteers had spent months preparing proper habitat for them.Each bird carries a small transmitter so that it can be located. During this year's breeding season, biologists were able to monitor 38 nests with radio telemetry. USGS project leader Michelle Reynolds said biologists have observed reproductive differences between the Laysan Island and Midway populations. The relocated ducks are breeding at an earlier age, she said, and are laying more eggs than ducks observed on Laysan, suggesting that the food or habitat on Laysan Island is limited.

Midway Atoll has a relatively low-density duck population and has abundant habitat and food, Reynolds said, possibly stimulating greater reproductive effort.

The U.S. Fish and Wildlife Service is a partner in the project.