A Noel Guard, invented by Jim Noel, is used to deter raccoons and cats from preying on the contents of nestboxes. It is useful for boxes mounted on trees and wooden posts that offer easy access to climbing predators. (Instead, I recommend mounting boxes on smooth metal pipe with a wobbling stovepipe baffle, which also protects the nestbox contents from snakes, and is more effective.) You can easily make one yourself, and only cost about $1 to make.
Make sure it is deep enough and securely attached (it can be stapled on) so a raccoon can not pull it off or reach past it to eggs or nestlings. If bluebirds have a choice, they may select a box without a Noel Guard. I think they should be put up after the first egg is laid to avoid scaring the birds away, although some folks have success leaving them up year round. The NABS website says this guard is estimated to be 90% effective in keeping raccoons or cats from reaching into the box. Some people find it does not deter raccoons, as they have long arms and a bendable wrist. Keith Kridler speculates that if the guard were 6-9" deep, it would deter all raccoons. Do not put these on boxes where livestock can rub on them as they can flatten them and trap nestlings inside. This guard does not deter snakes (use a Kingston wobbling baffle instead) nor does it deter starlings. They may deter Tree Swallows, and make it awkward for both swallows and bluebirds to feed young who were at the holes. Charlene Anchor of Illionis reports that wrens seemed to love them and would sit in them comfortably just outside of the entrance.
Wire mesh "hardware cloth" (ask for it at your local hardware store) - galvanized, 1/2".
Tin snips
A pair of pliers (to bend the wire tips)
Staples (to attach the guard to the front of the box.)
Instructions:
Cut a piece of hardware cloth 5.5" x 18". (Don Yoder makes the guard deeper - 7" to 9" - as he continued to have raccoons raiding boxes with a 5" guard. Joe Baker makes his guards 2.5" wide.)
Fold 15 1.5", 5.5", 3.5", 5.5" and 1.5".
Bend down and leave the pointy ends of the wire mesh pointing outwards
Bend in the vertical sides and attach them to the outside of the box with staples or screws, with the entrance hole in the center of the guard.
Jim Thompson created a Noel Guard Adapter, which is a block of wood the same width as the box front, with a corresponding entrance hole, that you mount the Noel Guard, and then secure it to the box with three screws. It is easy to carry around and mount.
