I don't know the scientific name for these but the Japanese name for them is Mejiro, pronounced mey-GEE-row (with the "r" in row rolled almost like a "D" or combination "L and R" combined sound.) They also know as Japanese White Eye.
They're really small and quickly jump from branch to branch so it's really difficult to get a good, close up shot of them. I'd say they're about the length of my middle finger...and I have kind of small hands. They're probably about 4" at the most.