Unidentified yellow and olive-green coloured small bird

On Wednesday, 21 November whilst walking home with my brother, I heard some small birds in the trees ahead of us. We were walking on the edge of the road on Douglas Street on the right hand side of the road between Francis and Pelham Streets before the Douglas Street bridge heading in a west direction. I could barely hear the birds, but they flew ahead of us as we approached the tree they were in. There were at least 2 of these birds. By the amount of calls that were coming from the closest tree I'm guessing it sounded like there were about 8 birds in the tree. We were about 10 - 14 feet from the trees as we walked passed them and the birds.

I took 3 videos as I approached the tree that the birds were in and as I was passing each of the 2 trees that the birds flew into but it availed to nothing. I did record their faint sound but no images of the birds at all. Just when I was about to give up on identifying the birds I saw one of them.

For a quick moment as the bird flew from a thick branch coming off the trunk of the tree to an inner branch with thick leaf cover, I saw a flash of colour and could roughly identify the birds. The one bird I saw was about the size of a Superb Fairy Wren, perhaps slightly smaller but was not a Wren of any kind. That much I could tell. The top of it's body was bright yellow and the underside of it's body was an olive-green colour. That's all I saw. It flew into the tree branch (from my left to a lower right position) too quickly for me to see what shape it was and what colour and shape it's head and beak was.

It seems really odd that most of the birds I have researched thus far that have yellow on them actually have yellow on their underside. Until now I had never seen a bird with yellow at the top of it's body.

The birds were quiet and seemed extremely shy, and obviously did not want to be spotted. I saw one of them as I was actually still looking at the tree, and was somewhat looking into the center of the tree as I was walking passed it. I had just looked down at the ground then looked back at the tree when I saw the bird.