Ralflow particles, in alambic, rendered with V-ray(Maya) in a quick sequence to go in compositing with Nuke X.
All the landscape is made with Mash in maya, to scatter vegetation, the birds are also made with Mash. Everyting is set to V-ray proxy's to make the scene lighter.
The animated hdri is made in Vue.
Nuke compositing timelapse
Animated HDRI with Vue