Hi Clive P, I once had a bat (pipistrelles) roost in my roof. In theory an ideal situation for getting photographs and observing - inside they can find a way of lurking out of sight (and being protected etc) and as they emerge - well you have a brief view of a head checking where they will go and then a blur as they head for an evening meal.
I used 7x50s to see some detail and retain dof, I must admit that like you in the end I gave up and used my eyes.
If someone came up with a reasonable quality zoom I would have used it with kingfishers over rivers. It would have been far easier to acquire at wide and track them zoomed in. Not sure that I would have had enough use to fork out for the Swavs but with use you never know.
I actually thought that I had once owned some zoom bins, but on checking I cant find any evidence - so must have just borrowed some once - I can remember trying to zoom smoothly but really ended up at one end or the other.
I actually think that from using video quite a lot that trying to manually zoom something the size of binoculars is always going to be a problem (someone please disagree) and power zooming works far better. I have the uncomfortable feeling we are heading back into the realms of Canon IS etc?, or the Duovid solution.
I miss the house with the bats - you could sit in the garden and not be eaten alive in the evening as they criss crossed above your head chomping away - great creatures.