Hugely fascinating observations. Yes, more bluebirds. Sorry to be boring, but it's my blog. And I adore bluebirds. They're an instant smile.
The bluebirds rest on a limb and search the ground from this vantage point. They see food, swoop down, grab and return to a limb. It may be a 1/2 second stop or it may be a couple of seconds on the ground. I've seen them return with big worms and white grub worms. The swoop and grab can be as fast as what the phoebe does, fly out, fly back with food. Fast as a blink.
One of yesterday's observations was amazing. The bluebird flew down and pecked at an acorn. There was a grub worm in the acorn. How did it know this? What was the clue? Movement of the acorn? Certainly a bluebird doesn't have x-ray vision, but there it was, happening at my feet. Now the earlier frame of bluebird and acorn makes sense and maybe that's why they like this particular field, loads of acorns on the ground.