Northern Prairie Wildlife Research Center
The usual method of attachment to a tree or wood pole is to insert a 4- to 6-inch lag bolt through a hole bored in the back of the box, opposite the entrance, and turn the bolt until the box is drawn firmly against the tree or post. Drill or punch a small hole into the tree in order to get the lag bolt started. Large washers should be used between the head of the lag bolt and the box. With a lag bolt the strain imposed on a box by a growing tree can be readily relieved every few years by a few loosening turns of the lag bolt. If heavy steel pipe or posts are used, it may be necessary to drill one or more holes in the pipe or post to bolt the box in place. The nest box should be fastened to its support so that it has a slight forward tilt. A backward tilt may prevent ducklings from climbing out and may also allow rain to enter.
When placed over water, structures should be high enough so that they will not be flooded. Four to 6 feet above the water's surface is acceptable to cavity-nesting ducks and also permits easy inspection and maintenance from a boat (Figure 13). It is best to place posts in water areas where they will not be destroyed by spring ice action.
Figure 13. Support piles and pipes driven in to the marsh bottom should provide several feet of free space between the bottom of the nest box and the surface of the water.
Poles for over water nests can be placed in winter when the ice is thick enough to safely support a person and/or vehicle (see chart). A hole slightly larger than the pole is cut through the ice with an auger or chisel. A special attachment for the auger blade is available which makes it possible to drill the hole into the frozen bottom of the lake. After the hole is drilled, a metal pipe or a 14-foot 4-inch x 4-inch wooden pole, with one end sharpened, is placed in the hole and forced by hand into the bottom as far as possible. The pole can be driven deeper into the marsh bottom with a post driver; several feet of the pole or pipe should extend above the high water level.
Ice Thickness Permissible Load
Less than 2" STAY OFF! 2" One person on foot 3" Group in single file 7 1/2" 2 ton truck gross (car or snowmobile) 8" 2 1/2 ton truck gross 10" 3 1/2 ton truck gross 12" 8 ton truck gross
If the ice is soft and slushy you will need twice the ice thickness to insure safety. Beware of crossing rivers, beaver lodges and lakes at their inlets and outlets since the flow of water under ice impedes freezing.