Hi trishytee,
Perhaps you could post the original uncropped picture aswell?
I have the 55-300mm pentax lens and have tried a few pictures of small birds at max zoom. I thought I could try and crop a similar pic to about the same size as the blue wren, to try and give you something to compare to.
Or perhaps have a look at the 2 bird pics in my thread here -
https://www.pentaxforums.com/forums/post-your-photos/71338-stormy-perth-australia.html
They aren't crops, but I did use the 55-300 @ 300mm. Fairly bad light too. I can get the exact settings if you like.
cheers
BTW - What an amazingly coloured bird - wish I had a pic of one