Yellow birds

No, not those in pants.

There seem to be a sudden influx of yellow birds today. I used to spot one or two around my old house and have never seen them around the current one until just now when I spotted about 4 to 5 of them in one tree, trilling away. They reminded me of wagtail in the Poldy series. Again they flew about in pairs and were awfully pretty but they seem quite large though, about the size of a mynah. They didn't seem to be so big previously, but that could be because I forgot. The yellow birds camouflaged into the tree and its leaves so well that I thought one of them was just an exceptionally yellow leaf. It amazed me how they were able to perch on a thin branch, swaying quite violently in the wind and it was this exact motion, or non-motion, that made me think it was a single yellow leaf.

I wonder why there are so many such birds recently and what are they called?

It seems so nice to fly.