Corella

Mid afternoon on a grey, windy day and the Corellas have roosted in a gum tree in the park out the back. If you look closely at the lower right of the photo there is what might be a Koala. I didn't see this until I brought it up on the computer so I immediately raced outside for another look,nothing there.so the mystery remains. Extras show the Corella flock just after taking off from the tree, I counted 73 birds,  and an plane with a top mounted rear facing engine. Any one have any idea what it might be?