I like the DOF you captured in #1 but would have cropped out the bird on the left. I think it works either way just mypreference
"Would be grateful if you would share your experience taking motion pictures of this kind using the reflex lens."
The flight shot is very good. Looks like you may have had an overcast day? Its tough to eliminate induced movement in low light conditions.Try using a tripod with a good ball head so you can pan smoothly as you track the flyingbird in the horizontal direction.I also useburst mode to increasemyodds of getting a good capture. I'll also change from spot focus to closest object to help in maintaining good focus as the bird flys through your feild of view. These are some of the techniques I use for flight shots I hope they help!