I have found and observed that after 2 relatively mild mating seasons here in North America, this years is especially strong. Salty has been driven to actively and relentlessly seek out dark hidey spots all around the house, which is totally new behavior for him, at 9 years of age. He;s had strong seasons before, which manifested in deep mood swings and bites, but not this new behavior. Also this year he's been exceptionally loud and long!
I wish I knew the external triggers, aside from the ones we commonly understand, that cause this variability from year to year! 40+ years ago, when my brother and I received a grant to study mating behavior and triggers in Burmese Rock Pythons, our theory was that temperature, humidity AND barometric pressure cycles were the main drivers, and the hermetically sealed huge tanks we made to control these were where the grant money went. Unfortunately the grant money dried up after a few years and we never did get conclusive data (and no baby snakes). But I suspect those (birds being so related to reptiles) are involved with parrots along with other factors. Birds unique Geo positioning abilities and others including olfactory and unique visual acuity to spectrum we cannot easily access could be involved in the variability. And then there is the acceptability of available mates to consider too; look at Merlin and Luna, 2 Amazons, same species, housed together for years and although I believe Merlin is willing Luna is not. As professional breeders know, the presence of male and female does not guarantee successful mating. More, careful and controlled study from the scientific aviculture community is needed ! Cornell University, are you listening?