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Creating a Wild Backyard - Predator Guards

Nest boxes are a great way to offer a home for birds that nest or roost in tree cavities.  However, nest boxes make these very same birds vulnerable to mammals and snakes that prey upon them, their eggs, or their young.  In order to really help these birds, you need to protect them to the best of your ability while they are using a nest box. Predator guards are simple to build, easy to install, and can save you and your bird guests a lot of heartache.

Predators of Nest Boxes
The most common predators of birds in nest boxes are raccoons, opossums, snakes and house cats.  Raccoons, opossums, snakes and other wild predators do more than satisfy their own hunger; they play an important role in the environment. These species and their prey have evolved together over thousands, if not millions of years, and their relationships tend to work by maintaining each other's populations at a stable level. That is, without interference from humans or catastrophic events! Nest boxes provided in response to a lack of tree cavities are actually interference from humans. In the case of the nest boxes and their inhabitants, humans are actually giving predators the advantage over their prey. Therefore, you need to protect the inhabitants of a nest box.

Predator Guards
Basically, predator guards prevent an animal from climbing up the tree or post on which a nest box is placed.  There are two basic types and both are made from 26-gauge sheet metal that can be purchased at building supply centers.

Sleeve Guard
For the first type of guard, wrap a strip of metal, at least two feet wide, around the tree or post. This design works best for nest boxes that are placed 10 feet or higher above the ground. Place the guard as high off the ground as possible, about six to twelve inches below the nest box. The strip can be nailed to a post, but when used on a tree, nail or staple the strip closed without damaging the tree.

Illustration Courtesy of the U.S. Fish & Wildlife Service

How to Build a Cone-Shaped Predator Guard
This type of predator guard is shaped like an inverted cone. Place the cone at least three feet from the ground or water where the nest box is located. You can find a pattern for cutting three predator guards from a sheet of metal on the back of this information sheet.

Materials

• 3' x 8' sheet of 26 gauge sheet metal

• Three wooden mounting blocks

• Galvanized nails

• 1/4" round head stove bolts or metal screws

• Tin snips

• Leather gloves

Construction

1. Mark the sheet as shown.  It will make three predator guards. 

2. Cut on solid lines only and follow the sequence of numbers.

3. Make circular cuts in a counterclockwise direction.
   Adjust the center hole cut to match the diameter of the post or tree.

4. To make the initial cut on line A-B; make a slot at A with a cold chisel.

5. Wear gloves when cutting.

6. Fold the metal circles over to make cones and overlap at the dotted lines.

7. Attach the overlapping area together with round head stove bolts or metal screws.

8. Attach the wooden mounting blocks to the post or tree so that the predator guard can rest evenly.

9. Place the predator guard over the post before attaching the nest box.  
   In the case of a tree, you will need to screw the cone together after placing it on the mounting blocks.

Plans & Illustrations Courtesy of the U.S. Fish & Wildlife Service

For Additional Information, Contact:
 
 Wild Acres Program
 Maryland Wildlife and Heritage Service
 Attn:  Marilyn Mause
 Gwynnbrook WMA
 3740 Gwynnbrook Ave
 Owings Mills MD 21117
 410-356-0941
 E-Mail: customerservice@dnr.state.md.us