They close down in late October or early November (depending on temperatures) and re-open in April (I think). We were there last for my birthday in mid-October and they were only going to be open for another week. They've got the birds (except for the ones in the nursery) outside on perches and temps can get very cold in the mountains during the winter, so they just close up through the winter months.
Here's their website:
http://parrotmountainandgardens.com/