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How to Make a Bird Trap Door

Despite its tiny frame and gentle appearance, the common house sparrow is a vicious competitor. If not controlled, they can destroy a purple martin colony. According to the Purple Martin Conservation Association, ".house sparrows will take over martin compartments for their nests, kill martins and their young, throw out or eat their eggs, and aggressively repel them." It is imperative that purple martin hosts have a method for capture and removal of cavity dwelling competitors.

Things You'll Need

Plastic sheet, 8-inches square by 1/16-inch thick
Felt-tip marker
Power drill
Hole saw, 1 1/2 inch
File
Drill bits No. 27 and No. 25
Metal plate 1 1/2 inch by 2 1/2 inch by 1/16 inch
2 bolts 6-32 by 1/4 inch
2 nuts 6-32
3 thin nylon zip ties, any length
12 inch piece of 10 gauge round wire

Instructions

Prepare Door Plate
- 1
  Measure and cut plastic sheeting to fit snugly inside the nestbox door. Trace the nestbox entrance hole onto the plastic door plate with a marker. Cut a hole in the door plate in the center of the marked area with a 1 1/2-inch hole saw. Smooth rough edges with a file.
- 2
  Draw a horizontal line on the door plate 3/8 inch below the hole. The line should start at the left edge of the plastic and stop 1/2 inch past the widest part of the circumference. Draw another line 1/2 inch below the first.
- 3
  Drill three holes, 1 inch apart, starting where the line ends at the right. Repeat on the second line. Thread zip ties through the pairs of holes. Fasten, but do not tighten.
- 4
  Drill a hole 1/8 inch from the left side of the hole with a No. 27 bit. Screw in a bolt. This will work as a stop for the metal plate.
Affix Trap Plate and Trip Lever
- 5
  Drill a hole in the metal plate at the center, 3/8 inch from the top with a No. 25 bit. Align the metal strip over the large hole leaving at least 7/8 inch of the plate at the top. Mark the plastic through the hole in the metal. Drill a hole with a No. 27 bit. Join the two pieces with a bolt. The metal should swing easily.
- 6
  Slip the wire through the zip tie loops on the same side as the metal plate. Pivot the metal plate on the screw until the long edge is horizontal to the top.
- 7
  Measure the distance between the bottom edge of the plate and the wire. Bend the wire at that measurement. Rotate the wire between the loops until the bent edge is flat against the door plate and pointing up. The metal plate should rest on the tip of the wire when the door plate is held upright.
- 8
  Bend the wire at the left edge in a "u-shape" back toward the right. Make sure the the first bend is still pointing up and is flush against the door plate. Manipulate the wire until it's horizontal with the wire in the loops and about 1/2 inch away. Cut off excess wire. Tighten the nylon zip ties. The wire should rotate easily.

Nature