Marilyn Michalski's Wren Guard

Title:  DIRECTIONS FOR CONSTRUCTING A 3-SIDED WREN GUARD.
BY MARILYN MICHALSKI – BSP BOARD MEMBER – Posted 12/16/22.
GOAL: TO “HIDE” THE ENTRY HOLE OF A NESTBOX FROM THE SEARCHING EYES OF HOUSE WRENS (HW)
This “guard” is a device added on TOP of a nestbox (NB) in order to deter House Wrens (HW) from finding the entry hole and piercing (killing) eggs laid by other cavity-nesters.  If successful, the Guard will force wrens to look elsewhere for a nesting location.  The success rate for keeping out House Wrens with this guard is 50%.    Recently, House Wrens (HW) have become over-populated, making them eager to usurp nestboxes meant for bluebirds and chickadees. Wrens will do anything to get a nestbox – they like to pierce the eggs of other species and stab hatchlings/nestlings to death, after which they toss them out of the NB. The major victims of the HW are the Eastern Bluebird and the Northern Chickadee. 
This “guard” functions as a shield over the entry hole and it can be raised up or down from a hinge at the rear of the nestbox. Before wrens arrive in PA from the South, the shield is raised up so the bluebirds and chickadees can find the nestbox and start their nests. From April 15th onward, the shield is lowered gradually, so that the front panel of the guard covers the hole, yet gives enough space so our “good birds” can enter the nestbox from underneath the panels of the guard.
SUPPLIES and TOOLS NEEDED:
A regular nestbox (NB), already completed, with a wood roof.
Hardwood plywood sheet – Approximately  3’ by 2’ – from which to cut out four pieces. These are: ROOF PANEL, FRONT PANEL, LEFT-SIDE PANEL, AND RIGHT-SIDE PANEL.   Note: ‘ = foot and “ = inches
A saw to cut out plywood panels (table saw, circular saw, hand saw, etc.)
One small 2-hole, or 3-hole hinge (attaches the rear of the guard’s top to the rear of the nestbox’s roof)
Small wood screws (about 15-18 of them) – size:  #6 x ¾” in length - all with Phillips heads.
Wood glue – the best is Titebond III.
A tape-measure or ruler of 12 inches in length.
Two clamps – to hold parts together when gluing and screwing together (optional but helpful).
Phillips-head screwdriver OR a cordless screwdriver with a small Phillips-head bit. 
An awl (hole piercer) can be used to mark locations of attachment screws. 
Some paper towels or clean rag.
Note: The four panels of this WREN GUARD are cut out individually, then glued together and also screwed to one another for permanence.  THERE IS NO ENTRY HOLE ON this WREN GUARD!  Its purpose is to BLOCKS the VIEW of the entry hole on the nestbox.
 
CONSTRUCTION:  (photos below illustrate process): 
Measure the size of the ROOF of your regular nestbox. Then cut out one piece of plywood to be slightly larger than the roof of your nestbox – by ¼ inch on 3 sides, but NOT the front.  YOU MUST ADD 3 INCHES TO THE ROOF PANEL FRONT, so that it JUTS OUT 3 INCHES IN FRONT OF THE NESTBOX ENTRY side.  After measuring carefully, CUT this piece out of plywood. This guard roof will measure approximately 11 inches long by 8 inches in width.   Then measure and cut out a “front panel,” to hang down from the end of the roof panel and block the sight of the NB HOLE. See photo below. It will be approximately 8 inches wide and 4 to 4.5 inches in height. Make sure it covers the entry hole on the NB when looking at the NB from ten feet away. In other words, this panel leaves about 2.5 to 3 inches of open space between the front of the NB (where the hole is) and the rear side of the front panel which hangs down in front of it. We want our bluebirds and chickadees to be able to fly into this nestbox – from underneath the guard. They are capable of doing this! Then measure and cut out the two side panels. They will both be as long as the “roof panel” and the same height as the front panel.  They will measure about 11 inches long by 4 or 4.5 inches high. Attachment of the guard parts: Have supplies ready to use: Glue (I strongly recommend Titebond III), clamps, screws and screwdriver. FIRST, glue the front panel to the roof panel by carefully applying a thin line of Titebond III along the front edge of the ROOF PANEL. Then, with a clamp holding the roof panel (of the guard) and front PANEL together, screw them together with two screws spaced evenly apart. If a screw misses part of the plywood, the glue will keep them together.  Option: You can glue the front panel EITHER to the front edge of the front panel, OR to the underside of the front edge of the roof panel. Whatever works for you. Next, check the fit of the two side panels with the front panel and the roof panel. Before adding glue, make sure each panel hangs down from the roof panel at a 90-degree angle (straight down) - AND that it can be glued to both the roof panel and the front panel- without leaving large spaces between parts.  Glue and screw together one side panel at a time.  Apply a very thin line of glue to a top edge and a front edge of a side panel.  If extra glue comes out of the seam, wipe it away with a paper towel or rag.  Then secure the seam with 2 or 3 screws spaced evenly apart. After both sides of the guard have been glued and screwed together, let this dry overnight. After the seams are firm (fully dry) it is time to attach the hinge. Make sure your hinge can connect to the TOP REAR OF THE TOP PANEL AND TO THE REAR OF THE NESTBOX ROOF.  Install with screws supplied in the hinge package, or with two of your own.  The hinge must allow the completed WREN GUARD TO BE RAISED AND LOWERED BY HAND. Optional:  You can paint the EXTERIOR OF THE GUARD WITH A TAN OR LIGHT COLOR OF PAINT. BE SURE TO USE ONLY EXTERIOR LATEX PAINT.  You can also use a few small wood blocks to put underneath the guard to keep the view of the nestbox hole open to view. When wrens arrive, you remove the blocks of wood to lower the guard and cover up the entry hole.  THIS IS THE COMPLETED WREN GUARD. YOU CAN INSTALL THIS WREN GUARD AND NESTBOX “COMBO” IMMEDIATELY. I USUALLY WAIT UNTIL FEBRUARY TO INSTALL IT, BECAUSE WINTER WEATHER TAKES A TOLL ON NESTBOXES.
 
PHOTOS:
#1 - Parts of the Wren Guard – partially assembled. The roof panel and the left-hand side panel have been attached. Note that screw hole locations have been made with an awl. The front panel is ready to be glued and screwed on. Then the final side – the right-side panel will be glued and screwed on. NOTE that the hinge has been attached to the guard. Also note the small screws and small wood blocks to raise up the guard – UNTIL THE ARRIVAL OF WRENS, WHEN IT IS LOWERED TO PREVENT THEIR SIGHTING OF THE NESTBOX ENTRY HOLE. By the time the Wrens have arrived, the bluebirds/chickadees should already be familiar with the Guard.
     
#2 - NOTE HOW EASILY THE GUARD CAN BE RAISED UP ABOVE THE NESTBOX ROOF.
        
#3 – BELOW: View of a wren guard interior before attachment to a nestbox.
 
#4 - Regular nestbox fitted with a Wren Guard   --   the nestbox entry hole cannot be seen. This means                the Guard is in the DOWN POSITION.  Also, note placement of entire NESTBOX in the middle of a clear patch of lawn. House Wrens like having bushes, shrubbery, and other greenery near their nestboxes, so we should locate our bluebird boxes away from these flora.