Allen: What delightful little critters. It’s a coin toss for me between #2 and #3. I love the light, pose and comp of #2 but the OOF BG twig bugs me a little. I would be sorely tempted to make that go away. #3 is just about perfect and your plane of focus and DOF management is superb. Really good effort. >=))>
These are all excellent, Allen, though I agree with @Bill_Fach about getting rid of that out of focus twig in the second. Since there’s no horizon, it’s difficult to tell for sure, but the 4th bird looks a bit unbalanced to me, like she’s about to fall off the perch, I might give it a touch of clockwise rotation. All the perches and backgrounds are gorgeous.
P.S. Bluebirds overwinter up here and usually don’t have any trouble, though the first year we had them nesting in our boxes was followed by a winter with a horrible storm (2-3 feet of snow followed by freezing rain) and we lost most of the young over that winter.
All are such nice images, but I could see a bit more contrast and exposure in #1 and contrast in #4. I agree with @Dennis_Plank about a bit of rotation in the last one. Even if the camera was level, the pose just feels a little unbalanced. Maybe prune the almost-horizontal grass stems?
Nice series Allen. Fine poses, perches and backgrounds. I find the first image rather dark as mentioned above and the details when viewed large seem rather soft. Still, all are fine catches and good suggestions above.