This challenge requires releasing 450 Blue Throated Macaws, however it appears that it is community based.
I had 12 blue throated macaws in my zoo, after releasing them all, I backed out to the main menu and went onto the community section and the challenge unlocked instantly. The community section states that it will show how far you are once you start the challenge (by releasing a blue throated macaw) so it seems you only need to release 1 bird, and go to the community section to get the challenge.
EDIT: you need Fame 36 to adopt blue throated macaws, they use a mini exhibit tree. 3 birds can be placed in each exhibit (though I'm almost certain you only need to release 1).