Hi Robin,
Ever since I've started visiting my in-laws on their farm in South Australia I've become familiar with the Blue Wren. I know how small they are, so getting close to them is important when it comes to making a photograph.
Now there's not a lot that I would really change with your photograph; lighting, exposure and composition are all suitable for the subject.
The question is, what can you do to improve this opportunity in the future?
If possible, I'd look into getting a remote shutter release for your camera. I would then place the camera - along with a wider lens - on a tripod near this particular post. Pre-focus the camera, set your exposure to the preferred mode and then sit in a nearby window where you can watch the birds coming and going from this position.
My aim with the set up would be to try tocapture not just the one wren, but two or more interacting with each other.
Photography shouldn't be a mundane task. It should always be about setting new challenges for yourself. Keep exploring this idea; I think you'll be surprised by what's possible.
Cheers, Anthony