They like the small seed --- the finch seed. If you put out some feeders only with finch seed & make sure they are near to cover so the buntings can get to safety fast then they will prove to be glutens. They will come back every single year & there will be more of them every year. Then you'll have to put feeders for them both in front & in back. I'm sure they like the meal worms too. they always arrived around Oct. 8th - 15th at my house & you could set your watch by them! They always left right around May 15th --- no later. I have a neighbor down there who has them year round. He has LOTS of cover in his yard & a gazillion feeders. Also, on Jupiter Island where they used to have the town hall (till a few years ago) they had feeders out & had the buntings year round. It takes time Lin.
Also & I found this very interesting --- the female buntings really like to come eat when a male cardinal is eating. They have some kind of odd partnership. Yes, they're both in the finch family but the female buntings won't eat alongside the female cardinals. The male bunting eats with the female buntings or alone but not with the female cardinals. You watch & see what you observe.
Indigo buntings also come down here for the winter. I saw one in my yard twice only & that was before the 2004 hurricanes. I didn't have any buntings at all for 2 years after those 'canes.