Greater vasa parrot - breeding female calling

Coracopsis vasa.
Greater vasa parrots are strange birds. When a female goes into breeding condition her plumage turns browner, she loses the feathers on her head and the bare skin turns yellow. She will mate with several males and when she leaves her nest, she calls loudly and flares her tail, demanding that the males feed her. You can see that the feathers near her mandible are matted with food provided by the males - if remember correctly there are four other birds in the aviary, so I presume they are all males. The female's 'song' could be heard around the zoo, it was a strange mixture of whistles and more typical parrot calls, but without any recognisable tune or pattern.