Raft of birds

We have just driven along the Coorong and watched as a very long raft of
birds moved from right then a turn left. The birds seemed to be led by large
group of Silver Gulls and on either side of the long line were the odd Cormorant
and even Grebe. The birds were in the thousands. Have never seen anything
like this before – they were not feeding, so I?m assuming they were getting
ready to migrate? It was quite a sight.
Robin