I was intrigued at the suggestion of cockatoos ringbarking trees, as to me it appears to be nonsensical. Not that they don’t bite at the bark, as they obviously do, and it can damage trees. Some information on parrot damage to trees is
at https://researchlibrary.agric.wa.gov.au/cgi/viewcontent.cgi?article=1133&context=rmtr .
However the idea that it is done by the birds for the purpose to ringbark trees is the weird and unnecessary extension of that it may be possible for particularly vigorous chewing might kill the tree. Parrots need trees with holes in them
for nests, the process of growing these holes takes many years. Can killing trees help them grow holes? It would take astonishing foresight and long term planning by an individual bird to come up with that idea, or, in evolutionary time a really complex chain
of phenomena to create the instinct. Yes they bite at bark: maybe for food, maybe to maintain their beaks (this is suggested by that they also like attacking built wooden structures), certainly to dig out larvae, likely to make the nest hollows more fitting
to their entry and exit or make a better nest cavity, maybe to mark their nest for territory. As for stopping goannas etc, on a rough barked tree it would hardly make a difference, on a smooth barked tree I would think it would make climbing easier. Many animals
mark their breeding territory. Certainly the rosellas that have nested in my nest box have chewed around the entrance of the box. They also clearly mark their breeding territory by display. Rosellas will perch on the nest box and indulge in their breeding
display of tail waggling and excited calling. This is very associated with the arrival of other pairs of rosellas (of either species) who also have an interest in the box and usually leads to a bit of fighting. Chewing the entrance may also provide a static
show that the box is probably occupied.
Philip
