African Blackwood, Cocobolo, and Osage are all favorite woods of us call makers. Dymonwood, acrylics and stabilized woods have become very popular in the last dozen or more years. Between the wetlands and calling process(blowing into the call) , duck calls must survive a very damp environment.
Finishing is an entire other topic. Many calls are finished with a BLO soak, some are lacquered, poly'd, and others use no finish at all with very oily woods.
Check out Greg Keets book on the duck call making.