Black insect in margarine turns into black bird

[roses]

I was at a house that my mother owns. I opened the refrigerator and there was a black insect (I think a fly or spider)in the margarine. The insect's body was half way in and half way out of the margarine. I took out the margarine and the insect turned into a black bird. The bird was about the size of a cockatiel. The bird was sitting on my finger and was kind of heavy. He did not look sickly.