A Walk-in Trap For Nesting Ducks

We trapped on private land in west-central Minnesota in 1987 at mallard nests protected by portable electric predator exclosures. Mallard females also were trapped at 2 predator-reduced nesting islands and on an electric-fenced peninsula in eastern South Dakota during 1990-1991.

Materials

Materials for each trap included 2.5- × 5-cm galvanized welded-wire fencing, 2- × 2-cm black nylon monofilament mesh garden netting, hog rings, wire-cutting pliers, hog ring pliers, and 4 or 5 stakes/trap. Welded wire and garden netting cost approximately $1.60/m², and $1.00/m², respectively. Stakes cost $1.50 each and were constructed from steel rods approximately 1 cm in diameter and bent into a j-hook. When necessary, stakes were fashioned from tree limbs found near the nest site. Including 5 stakes, material costs for the trap approximated $13.50 (1993 U.S. currency). About 15 minutes of labor were required to build 1 trap.

Exact size of fencing and garden netting depended on the dimensions of individual traps. Trap size was variable because of differences among nest sites and because we built several traps during our first field season without regard for constancy of size. We used traps ranging from 60-100 cm in height and from 50-80 cm in diameter.

Trap Construction

First, we cut the welded-wire to the desired dimensions. When wire was cut to a shorter height, we placed the cut edge at the bottom to avoid injury from sharp ends. Second, we brought the edges of the trap together to form a lily-pad shape (Fig. 1); horizontal wires on each edge were cut flush to the vertical wire so that no sharp ends projected into the trap. Edges were fastened together with hog rings, starting at the top and leaving the bottom 30-40 cm unfastened. Third, we created the funnel entrance in the unfastened opening by folding the bottom edges of the wire inward. The funnel was 30-40 cm high, with the opening 15-cm wide at the narrowest to allow ample room for the duck to enter and leave the trap. Fourth, a piece of garden netting was cut large enough to cover the top and halfway down the sides of the trap. The excess netting facilitates setting the traps in vegetation of varying heights. Every 6th to 8th wire in the second row of vertical wires from the top of the trap was cut near its base and bent outward slightly to provide attachment sites for the garden netting (Fig. 1). Excess netting was rolled up and pushed under the bent portions of the welded wire to hold the netting securely to the trap.

Fig. 1.  A walk-in trap for capture of nesting ducks

Trap Placement

We suggest that traps be set only during late incubation to minimize nest abandonment. When setting the trap over a nest, minimize disturbance of vegetation. Surplus garden netting can be shaped over vegetation of different heights. Paths used by females to enter and exit a nest site can be determined by observing the female as she flushes and from vegetation characteristics. To avoid the female finding the entrance quickly and thus escaping during capture attempts, we positioned the trap so the entrance was to 1 side of the female's normal path. We set some traps with the entrance completely opposite the path with no apparent effect on trap entry or nest abandonment by females. Traps should be positioned so nests are maximally away from the funnel opening. We staked the opening so it remained about 15-cm wide across the narrow portion of the funnel. We finished setting the trap by staking the bottom perimeter to the ground.

Trap Visitation

In areas where mammalian predators do not occur or have been greatly reduced (e.g., nesting islands, electric predator exclosures), traps can be set and checked the following morning. If the female is not captured, the trap could be reset for further attempts. In areas where mammalian predators such as red fox (Vulpes vulpes), raccoons (Procyon lotor), and striped skunk (Mephitis mephitis) are present, we suggest setting traps only during daylight hours to avoid peak periods of predator activity (Jones et al. 1983; A. B. Sargeant, Natl. Biol. Surv., Jamestown, N.D., pers. commun. 1993). We feel the walk-in trap would make the female more vulnerable to capture by a mammalian predator. We attempted to capture females prior to 1200 hours to allow them ample time to return to the nest before dark.

When examining traps, we moved quietly to approximately 40 m from the nest and then rapidly approached. On reaching the trap, we blocked the entrance with a dip net or a similar object. We retrieved the female through the top of the trap by pulling away a section of the netting from the bent-out wires.

After capturing the female, we removed the trap from the nest, rearranged the vegetation if necessary, and covered the clutch with down and nest material. If the female escaped before the entrance was blocked, we often reset the trap on the nest site with the entrance in a different location to thwart subsequent escapes by the female. When traps were reset with the funnel in a new location, females usually did not escape before the entrance was blocked.