A unknown bird's nest at the front door

This is our front door. Just a painted wooden door, nothing unusual.
This spring, we bought a new silk flower garland and replaced an old one (center of the door).
There are two decorative plastic trees at both sides of the door.
We have had bird's nests in this plastic trees every year.
They used to build nests inside the plastic leaf-ball.



Close up of the new flower garland. It is made up with silk flower, plastic leaves and natural vine frame.

On July 9th, 2012, my wife noticed an some extra twigs bulging out at the right lower corner.



July 9, 2012: She took a closer look and found one small bluish egg in a newly built bird nest.
The nest was built with dried grass, dead tree twigs, and dried iris leaves in the yard.



July 10, 2012: We found two small eggs in the nest. No mother bird was seen.



July 11, 2012: Now there are three eggs. We noticed a small bird flying out in the morning.
But it seemed that the nest stayed empty most of the day.



July 12, 2012, there were four eggs. The eggs seemed to have been rotated around
because the dots on the eggs seemed to have been changed to different places on the eggs.
One egg was much smaller than the other three.

From July 13, 2012, we noticed that there is a small bird in the nest even during the day.
On July 15, 2012, while the mother bird was out, I took a peek and there were only four eggs and no more.
We have completely stopped using the front door.
Because of the location of the door, there was no way I could take the picture of the mother bird in the nest.
I decided to wait until the eggs hatch. I am studying a way to take pictures of the baby birds without disturbing them.

I have not been able to identify the bird. I am sure that she's not a robin by the size.
It could be a small finch or a similar bird.