I've ordered this "Woodpecker Suet Cake" at least 3 times, and a few kinds of woodpeckers and the cardinals are big fans. I ran out of the cakes and picked up three blocks of a different brands in different compositions to use until my next order could be delivered and was quite surprised that the birds didn't like them. One was barely nibbled at, one looked as if it have been tasted and deserted, and the third, was completely untouched.
As soon as I placed the freshly ordered ones up, they start to show up again. I discarded the replacement on the ground for the raccoons, who can't get to the hanging ones.
You can get this Woodpecker Suet Cake from here - Amazon