Northern Prairie Wildlife Research Center
Metal structures have the advantages of being longer-lived and, if constructed properly, are difficult for predators to enter. The disadvantages are that they can be more difficult to construct, may not be as aesthetically pleasing, and have no insulating value. Recently, discarded empty freon canisters have been used successfully to make aesthetically pleasing metal nest boxes (Figure 10). (CAUTION: Freon is hazardous to your health and the environment. Freon tanks must be emptied by a certified technician using appropriate equipment before being cut open.) Plastic buckets or other thin-walled plastic structures have been used for nest structures, but they have no insulating value and become brittle when exposed to the elements, especially in northern climates. Some good wood and thick-walled plastic boxes are commercially available.
Whatever type nest box you choose, it must have a ladder, usually made of 1/8-inch to 1/2-inch hardware cloth, to enable the ducklings to exit. The ladder should be securely attached to the inside of the box just under the entrance hole and extend to the bottom of the box. All structures should have drain holes drilled in the bottom to help keep nest material dry.
Although wood ducks naturally nest in tree cavities, we recommend, at least initially, that boxes be mounted on posts over water. Over-water boxes are less likely to be disturbed by predators and are less frequently used by other animals. Steel pipe makes the best over-water, long-lasting post. The best choice, especially if 2 boxes are to be mounted on one post, is heavy duty pipe with at least a 2-inch inside diameter. U-bolts can be used to attach the box to the pipe or holes drilled in the pipe and the box attached with bolts and fender washers. If wooden posts are used, they should be at least 4 inches in diameter, cedar or treated wood, and must be protected with a predator guard (Figure 13). The top of the predator guard must be at least 3 feet above the high water line. For more details on posts and installation techniques please read the section "Canada Geese - Post Structures", and see Figure 3.
Boxes should initially be erected over water so the bottom of the box is 4 to 5 feet above the normal high water level. Boxes should be installed in 18-inch to 36-inch deep water and preferably near potential wood duck roosting or loafing sites such as flooded willows, buttonbush, downed trees or emergent vegetation. One box every 2 acres is plenty to start with, but as many as two boxes per wetland acre have been used successfully. Because wood ducks are tolerant of one another, up to 4 boxes can be mounted on a single post provided it can support the weight.
Once a box-nesting population of wood ducks has been established, it is possible to move the houses to shore. However, every care must be taken to protect the hens nesting in over-land boxes from predators. Placing boxes on shore in isolated locations, preferably in the woods, will help reduce dump nesting and conflicts between nesting hens. When placing boxes over dry land, the bottom of the box should be 6 to 10 feet above the ground and away from any overhanging branches. All pipe or wooden posts installed over land must be protected with a predator guard so the top of the guard is 5 feet above the ground (Figure 13). If houses are erected in trees, the tree should be isolated from adjacent trees and the trunk completely wrapped with 30 to 36-inch wide galvanized sheet metal. If the tree is not isolated, predators may be able to reach the box by jumping from adjacent trees.
Another method of erecting boxes in trees that is relatively predator proof is to use the S-pipe mounting bracket illustrated in Figure 14. This bracket is normally made from pipe with a 3/4-inch to 1-inch inside diameter. However, this mounting technique can only be used with metal houses since squirrels and raccoons can easily jump on to the top of a wooden box.