A sizeable flock of Yellow-tailed Black Cockatoos flew in from the west in small groups before doubling back to land in some eucalyptus trees. I had heard them for most of the time I had been at Cotter Bend but I had not seen them. My first sighting of them was in the ridge to the north-east of Cotter Dam. I am not sure how many birds there were but at least 20 would be a reasonable estimate. They were moving between trees, calling as they progressed.