Do herons practice nest-building?

[loripo]

This is a still from a video clip I took a few weeks ago in our local park, where there are about 30 established herons' nests. These have been occupied for a couple of months now. As you see this one had broken off a small branch and was trying to place it in a fork of a tree.
I did put that clip with some others of herons on to the www schoolstube dot com website today and it is now showing as 'recently added' - it's only about 3 mins and the 'twiggy' part is about halfway thru. If you click on download and watch on your media player rather than go full-screen it's usually better. I would really like to know if they do have trial runs, and if this is at any time of year. How long does it take to construct a usable nest?
If by the time you decide to watch it's off the front page, click on 'animals' on the left hand side (Just covering all bases...)

[loripo]

I had a look to see if there was any evidence of a new nest, but couldn't see any. Perhaps 'Twiggy' gave up
This is the next tree along - an established nest with at least two young, possibly three. All making a great deal of noise yesterday and lots of activity with adults coming and going. Looking at the photo I realised just how loosely the nest is constructed. Lets the wind through I suppose.