What I've done for large round holes is.
1. Nail a tin can lid over it (Needs to be repainted)
2. Cut out a plug from a 1/2" pice of wood I had in the basement with a saber saw and glue it in.
You can spray CRC Minimal Expansion Foam Sealant in hole first to keep the plug from falling in.
Then use plastic wood to fill the gaps around the edges and paint.
Both of these solutions passed inspection when selling my home.

Small holes:
1. Use caulk *. The gray caulk matches the color of my siding so I don't have to paint.
For anything larger than 1/4" it shrinks leaving a dimple.
So, then I use plastic wood. You might find a color to match your siding so you don’t have to paint it.

Other choices for large holes.
3M Bondo Home Solutions Wood Filler (epoxy)
Abatron WoodEpox Epoxy Wood Replacement Compound See wood filler
* Caulk - Acrylic Latex is best. See the Caulk page.

Links:
Bird Control - prevention
Repair Woodpecker Damage - The Woodpecker Remover

last updated 23 Mar 2018