Peter, thank you for the comment - which certainly helped a lot in terms of getting to the right answer.
I ended up contacting the Bird Gardens where I took the pictures and was advised that it was most probably a "Blue-bellied Roller". A quick PBase search showed up a couple more examples (example:http://www.pbase.com/image/21347481) and "googling around" confirmed that it is indeed this "Blue-bellied" version of roller.
All these Bird Garden shots were done with the lens handheld, but this is indeed somewhat of a challenge due to size and weight. I am sure it would have worked a lot better on a tripod.
