Lesley and I have established a connection and are both now looking for Francis Birkett and Eleanor Oglenby (or Ogleby).
However, in my family the legend about Birkett being a Viking name is one I grew up with. It comes from a birch tree and he was the man who sat under or in a birch tree. I don't know if that means if they were some kind of shepherd - or if they were the lookout men for the Vikings. (Given the state of the eyesight of the current crop, if that was the case they were probably looking for America!!!)