How do you explain - -

[Dao]

I would expect this without flash but was counting on the flash freezing them. Perhaps I just had too much light behind the drops allowing the motion to be seen.

Flash will only freeze motion at slow shutter speeds when there is no abient light

Well, I have seen pics of humming birds frozen in flight by flash in daylight & that is what I was taking my cue from.

What about the flash power? And where the flash is located. I remember saw a setup where the photographer use few flashes (quite powerful) close to the bird (where he had something there to attract the birds) and took photo of the bird ...... maybe from a distance.

Maybe because of the flashes over power the ambient light (together with smaller aperture or higher shutter speed with HSS)