Interesting and all quite believable. There are a couple bits of context to add. Clearly the behaviour of these captive birds is not fundamentally different
from wild ones but relatively intelligent animals can in captivity lead to boredom and sometimes odd and compulsive behaviour (obsessively doing something they would normally do to a lesser extent), which is suggested by this story. The wiping the beak and
face on the branch can be an extension of the chewing behaviour or can equally be for a quite different reason of beak cleaning, display, or head scratching, they may likely find the face scratching pleasurable.
I earlier wrote to John Leonard
As possums can climb smooth and rough barked trees, it is hard to see how this would create a smoother surface and so that would appear unlikely to be a successful strategy.
I suspect the same applies to goannas (maybe not snakes) so I’m not convinced that the idea of making it harder for climbing predators works very well.
Or maybe just making it slightly harder is sufficient benefit to change the odds enough..........
Philip
From: John Harris
Sent: Thursday, 30 July 2015 10:07 AM
To: Canberra Birds
Subject: Re: [canberrabirds] Ringbarking by Galahs
Galahs like to chew and that chewing can become damaging. My Grandfather used to hand raise Galah chicks which were given to him by timber workers who had
felled nesting trees. He gave them away if he could when adult. He got into trouble once for releasing them back to the wild because local farmers regarded them as pests.
I had a breeding pair he gave me for many years as a boy and youth. I used to supply them with a new semi-hollow log every year because they loved chewing
at it so much. They enlarged the hollow and chewed off the bark all around the entrance. They took a lot of care about that area, chewing off even the smallest rough piece and then rubbing it smooth with the side of their beaks. I always gave them leafy branches
to play with and because they liked to eat lerp and scale and such. In the breeding season they would get Eucalyptus leaves and rub them on the area they had smoothed outside the hole and even polish the smoothed wood with their cheek feathers.
They were very turned on to this activity and it seemed never finished to them. They would gradually remove all the bark from the log and extend the smoothed
area up to a metre sometimes.
I often wondered what was the point of the smoothing. I though maybe it was just removing uncomfortable rough bits but Grandfather thought that in the wild
it was to make it too slippery for predators such as lizards to enter the nest. Evolution of behaviour is a fascinating thing. I am certain that predators were not in their minds and I am equally certain they liked doing it and were reluctant to stop while
ever there was bark to chew off.
I think some of the recent postings border on confusing instinct with intent, if those are the right words. It may well be that the ringbarking of trees eventually
produces dead trees with good nesting hollows but that takes many years. The galahs enjoy the activity, some no doubt more obsessively than others. It is not however an intent to create future hollows. Personally, I just think they like doing it and that this
energy is concentrated in the breeding season.
