You can mash up cat food and soak it in warm warm water for about a minute and then get a syringe (with no needle) or eyedropper and put your mixture in that then put it into the baby woodpeckers throat...
What Does A Baby Woodpecker Eat?
You can go to www.wikipedia.org, and type in woodpecker, some information there. You might also call an aviary store, that would be a bird store. Hope this helps, good luck.