Northern Prairie Wildlife Research Center
Two types of elevated nesting structures have been successfully used in North Dakota. These are wire basket structures and fiberglass structures. Both are of similar shape and design. Both types are accepted equally well by mallards, and Canada geese also occasionally nest in them. The wire baskets may cost less than the fiberglass structures; however, there is considerably less work involved in assembling the fiberglass unit.
The wire cone is cut from 1/2-inch hardware cloth, 36 inches wide. The cloth is first cut into 36-inch squares, and then the 18-inch square unused portion is cut out (Figure 1). The cloth is then formed into a cone and is tied in this position with soft wire. The basket frame is constructed from a 24-inch section of 1-inch I.D. pipe and four 1/4-inch x 12-inch hot rolled steel rods. The 1/4-inch rods are welded to the pipe and then bent out to accommodate the basket frame rim as shown in Figure 2. An additional 82-inch length of steel rod is used to form the rim of the basket frame. The wire cone is inserted into the basket frame and the corners of the wire cone are bent down over the rim. The cone is fastened in place with soft wire.
The inside diameter of the basket frame pipe shown is 1-inch but can be changed to match the available material used for the nest support pipe. This pipe can fit either inside or outside the nest support pipe. If it is fitted outside the nest support pipe, two holes should be drilled opposite each other about 3 inches from the top and 1/4-inch or larger steel rod inserted to prevent the nest support pipe from punching through the bottom of the wire cone. The nest structure support may be any metal material available that is rigid enough to support the nest basket and attaching assembly. A smooth, round, non-corrosive pipe is preferred as it is harder for predators to climb.
A threaded hole for a setscrew should be tapped about 3 inches from the top of the support pipe. When tightened, this setscrew will give stability to the basket and permit raising or lowering it as water levels change from year to year. A 7- to 8-foot support pipe usually is satisfactory. The pipe length, however, will depend on the firmness of the marsh bottom and water depth (Figure 3).
The supporting 2-foot piece of pipe is attached with an ordinary floor flange. This is done by drilling four holes in the flat base of the cone to match those in the flange and then bolting the flange in place with small bolts and washers of appropriate size. One end of the 2-foot length of pipe must be threaded so it can be screwed into the flange. The size of the flange depends on the pipe available. A satisfactory combination is a 1-inch floor flange into which is screwed on to a 2-foot length of 1-inch I.D. pipe. The 1-inch I.D. pipe telescopes into a 1 1/2-inch I.D. support pipe which is driven into the marsh bottom. A 5/16-inch hole is drilled 2 inches from the top end of the 1 1/2-inch I.D. support pipe and is threaded with a 3/8-inch N.C. tap and fitted with a 3/8-inch x 1-inch N.C. capscrew, as in the wire basket structure. Four 3- to 3 1/2-inch diameter holes are drilled into the sides of the fiberglass baskets prior to their installation. This is done to permit wiring of the nest material in place and also to enable ducklings to escape if the level of nest material becomes too low, preventing the young birds from leaving the nest structure. These four holes are spaced evenly around the basket, the upper edge of the holes being 5 inches below the basket rim. In addition, one to four 1/2- to 1-inch diameter holes are drilled near the bottom of the cone to allow drainage (Figure 4).
An enlarged version of the basket structure has been used by giant Canada geese and mallards. This jumbo-sized structure has a basket diameter of 36 inches and it is supported by a 2-inch pipe.
In localities where both giant Canada geese and mallards are found, it may be advisable to put out the larger nesting structures which are recommended for geese. Mallards will also nest on these larger structures.
It is very likely that any of several types of basketlike structures would be acceptable to mallards. For this reason, there is much room for innovation in constructing nesting structures from excess or surplus materials, thereby reducing the costs.
|Fig. 5 Flax straw is the best nesting material since it holds together well and resists being blown from the structure by wind.|
The nest material is installed by packing loose straw or hay into the lower half of the basket (Figure 6). Above this is placed a circle of straw or hay which extends slightly above the level of the rim of the basket. This doughnut shaped arrangement of nesting material is secured in place on four sides of the basket with light wire (Figure 2). The wires are threaded from the outside into the hardware cloth in the side of the basket, up through the nest material and over the rim of the basket. These wires should not cross the center cavity where the eggs will be deposited. The center cavity should be about 4 inches deep. If necessary, additional loose nest material should be pressed into the center to provide this depth (Figure 6).
|Fig. 6. Pictured above is a wire basket properly filled with flax straw nest material. All nest structures must have suitable nesting material installed annually.|
For fiberglass baskets, wires are threaded from each of the four escape holes into and up through the edge of the doughnut shaped circle of nesting material and over the rim of the basket. The wires are then pulled together, twisted, and the ends clipped off.
|Fig. 7. Open water at the edge of cattails, bulrushes or other emergent cover, or small patches of open water in stands of such cover provided good placement sites.|
The support pipe should be driven into at least 1 foot of solid earth in the marsh bottom. Place the structures where they will not be exposed to excessive ice and wave action during the spring breakup. Late fall or early winter is the best time to drive the support pipes into the marsh bottom. After the ice is thick enough to support a person, it is relatively easy to pick up suitable locations and drive the pipe. An ordinary steel post driver is satisfactory for installing the pipe after a hole has been made in the ice. At this time, the marsh bottom will be unfrozen, and it will be easier to determine whether the pipe is firmly anchored so it will stay in place. If the ice is thick, a power driven ice auger of the kind used by winter fishermen can simplify the task. Some augers have a special attachment for the blade which enables it to cut into the solid earth of a marsh bottom. The nest structure need not be attached at the time the support pipe is driven, but it is desirable to do this before the ice breaks up in the spring. Support pipes may also be driven in during other seasons by standing in the water or working from a boat.
When in place, the bottom of the basket should be at least 30 inches above the water level, but heights of 36 to 48 inches above water are recommended. Ordinarily, water depths of from 1 to 3 feet are satisfactory for installing the structures. The possibility of changing water levels should be considered and structures should not be placed in situations where the level is likely to rise to less than 18 inches from the base of the basket. It is recommended that structures be placed on ponds that hold water at least through mid-summer. Ice, wind, or wave action may cause some structures to tilt or fall after the first year. This fault may be corrected by moving the baskets to sites which are more protected or have firmer bottoms, or by driving the support pipes deeper.
A rule of thumb is to situate the structures as far from shore as possible, staying within adjacent emergent cover types and range of water depths. Another rule of thumb is to avoid placing large numbers of structures in a marsh. A single structure may be sufficient for a small pond or pothole. However, four to six may be placed in a marsh 25 acres in size or larger by spacing them as far apart as possible. If these structures are used by nesting hens, more can then be added.
|Fig. 8. Nesting baskets should be inspected and serviced annually, preferably prior to April 1.|
Structures that consistently receive no use may be moved to new locations where they may be more acceptable to female mallards.
Both wire and fiberglass baskets will stand in place and otherwise hold up in usable conditions for many years. Many have stayed in place for 12 to 15 years.
When installing or servicing baskets in winter, the nest material can be secured in place in a shop or warm indoor situation. Then the completed basket assemblies are taken to the field and mounted on support pipes which are already in place. This procedure may involve removing the baskets, servicing them, and returning them to the field, but in periods of very cold weather it may be worth the added time and effort.
When servicing the basket during the winter by driving on ice, avoid leaving trails that lead directly to the basket. Vehicle trails through emergent cover make excellent predator lanes. If using a vehicle, it is better to enter the pond from the shore opposite the basket.
Hawks and owls may occasionally perch on a nest in these elevated nesting structures. Usually the incidence of this type of use is quite low and is not great cause for concern.