"A whole lot would depend on whether Polly chanced to get free during those particular days when the spoons disappeared.

As to whether a bird like that would carry away such things, and hide them, there's lots of accounts of such things happening.

I'll tell you of a few instances I've read about, and every one was vouched for as absolutely true in the bargain." So for some little time he amused and interested the old lady with accounts of strange things various species of pet birds, from rooks and ravens, all the way to talking parrots, had been guilty, in the way of stealing bright articles of jewelry, and trinkets that seemed to have caught their fancy, hiding them away in some cranny or nook, where the whole collection was afterwards found.
"I may have read something along those lines myself at some time or other, Hugh," she told him, as he concluded, "but it slipped my mind.
Whether Polly is guilty of petty larceny or not, after this, I shall be more careful than ever about keeping her fast to her perch by that long chain.

There is no telling what a wise old bird of her nature might not attempt, given freedom.

I sometimes think she has a little devil in her, when she says something wonderful, and looks so droll.