Northern Prairie Wildlife Research Center
The Gjersing structure consists of a 3x4 foot wood frame platform supported by an angle iron frame attached to three 10-foot long pieces of pipe. Two hay bales are placed on the platform for nesting (Figure 3).
|Fig. 3. Canada geese quickly accept the bales used in the Gjersing structure. (T. Hinz)|
It is a sturdy structure, but the wood platform may need to be replaced periodically. Annual inspections are also necessary to determine if haybales should be replaced.
This structure is more difficult to install than the elevated North Dakota structure, but its high first year use more than offsets this difficulty.
A major advantage of this structure is that it can be constructed from scrap pieces of wood, pipe and angle iron.
|Pipe||30 feet 2 to 3-inch diameter pipe|
|Angle iron||14 feet 1-inch wide x 1/8-inch thick|
|Wood||12 board feet of rough lumber in either 3 or 4 foot lengths|
|Bolts||Three 31/2 x 3/8-inch galvanized hex bolts, nuts, flat and lock washers.|
|Wire||20 feet of 10 gauge smooth galvanized wire|
|Bales||2 bales of flax straw or hay|
The materials are prepared in a shop before going into the field. Oil well tubing (2 3/8-inch outside diameter) which comes in 28- to 30-foot lengths has been used in Montana to make the structure support pipes. These longer lengths can be cut to give three equal length pieces. Each piece must have a 25/64-inch diameter hole drilled about 8 inches from the end.
The 14 foot piece of angle iron must be cut with 45° mitered ends into two 4-foot pieces and two 3-foot pieces. These are then welded in a 3- by 4-foot frame. Each frame should then have a 25/64-inch diameter hole drilled into it. One hole is drilled in the center of one 3-foot side. One hole, six inches in from each corner, is then drilled on the other 3-foot side (Figure 4).
|Fig. 4. Top view of frame with boards in place showing locations of holes in angle iron for bolting to support pipes.|
Boards should be cut to fit after the frame is welded. The boards can fit loosely together in the frame. These can be either 3-foot length boards laid cross ways or 4-foot length boards laid lengthwise in the frame.
Once the frame is assembled and the holes are drilled in the support pipe, the structure can be erected in the field (Figure 5).
|Fig. 5. The Gjersing structure is a sturdy platform which can be used in a variety of wetland habitats.|
Once you have selected a site, make a hole in the ice and drive the first leg of the structure into the bottom until solid. Lay the frame on the ice so that the single hole drilled in one of the 3-foot sides is butted up against the middle of the pipe. Mark the placement of the other two legs with an ice chisel, chipping the ice on the outside of the frame near the two holes drilled in the opposite 3 foot side of the frame. Chip out the second and third holes and slide those legs in until they touch bottom. Tip the legs until they appear vertical from two directions from a distance of at least 15 feet. Drive the remaining two legs in until: 1) they are solidly set in the bottom, 2) the drilled holes are about a foot above flood level, and 3) the drilled holes are about the same distance above the ice. Once the legs are set the frame can be attached.
Bolt the frame to the legs inserting the bolt from the frame side through the leg. Add the flat washer, lock washer, and nut in that order on the outside edge of the pipe, then tighten until snug. Make sure the frame is level. If it is not, drive in the high pipe(s) using the closed end of the driver.
Insert the boards in the frame, set the two bales on top (cut ends of the bale up and down) and wrap wire around the bales and platform near the ends of the bales. The wires should be tight. Tighten by pulling with one hand and using a lineman's pliers to pull on the other end. Tightening should be done using the frame edge for good mechanical advantage. Once the bales are wired in place, the structure is ready for geese.