Thanks Eric. This is one set of Bluebirds. They (I think its the same set) have been building a nest in our bird house for the last 5 years. They are very territorial. I watched as both the male and female ran off another pair. I had to go out and run them off after they pinned the other male on the ground and were pecking it to death.
Also you are correct its a 300 f/4 with 1.4 TC.