Research wildlife biologists from the US Department of the Interior/US Geological Survey got in the cold waters of Arrowhead Marsh at Martin Luther King Jr. Regional Shoreline in Oakland on Wednesday.

The biologists searched for California clapper rail birds, an endangered species that lives in the bird sanctuary. They found ten of them and replaced radio transmitters on their upper back for tracking migratory purposes.

Also, biologists got blood samples and measured the birds before they were released back to their habitat. The project is held once a year at this location.

A flock of birds fly over Arrowhead Marsh at Martin Luther King Jr. Regional Shoreline in Oakland, Calif., on Wednesday, Dec. 4, 2013.  Wildlife biologists
A flock of birds fly over Arrowhead Marsh at Martin Luther King Jr. Regional Shoreline in Oakland, Calif., on Wednesday, Dec. 4, 2013. Wildlife biologists from the US Department of the Interior/ US Geological Survey searched for California clapper rail birds, an endangered specie that lives in the bird sanctuary. They found 10 of them and replaced radio transmitters on their upper back for tracking migratory purposes. Also, biologists got blood samples and measured the birds before they were released back to their habitat. (Ray Chavez/Bay Area News Group)