Australian Corellas

Woken at first light by the Corellas, and they hang about in the 100s all day, Sounds bad but you get use to them and they become background noise, They are interesting to watch especially when they fly up the river in there flocks, gathering more as they go, i would say there were 1000 at one point. It is quite understandable why the farmers consider them pests, they sit in the Gum trees pecking small branches off, so what do they do to crops?