Short answer: Window bird feeders are usually 1/8 in. clear acrylic: light enough to hang from suction cups and clear enough that you can watch birds feed from inside. Drill holes for the suction cups, add small drain holes in the tray, and either solvent-bond the parts into a box or bend the back and tray from one piece.

How a window feeder works

A window feeder is a clear back panel that sticks to the outside of the glass with suction cups, plus a tray or seed box on the front. Birds perch on the tray lip and eat while you watch from a few inches away. Because the back is clear, the view through your window stays open, and window feeders can actually reduce window strikes, since birds arriving at a feeder that close aren't moving fast enough to hurt themselves.

What size and thickness to choose

Most window feeders are 6 to 10 in. wide and 8 to 14 in. tall, with a tray 2 to 3 in. deep. Small enough to stay on with two or three suction cups; big enough for a couple of chickadees or finches at once.

  • 1/8 in. clear for the back and tray. Light weight is the whole point with suction cups.
  • 3/16 in. for larger feeders, or a roof that bigger birds and squirrels will land on.

Clear cast acrylic holds up outdoors for many years without yellowing much, and it survives freezing winters. See can acrylic be used outdoors.

Three ways to build one

Bent back and tray

The simplest design is a single strip of 1/8 in. acrylic with one bend near the bottom: the long part is the back, the short part folds out as the tray. Add short side walls bonded on to hold seed in. We can line-bend the tray to a crisp 90°.

Bonded box

A back, a front lip, two sides, and a floor solvent-bonded together. It's the most watertight and the most finished-looking. We build these as bonded assemblies, or you can glue it yourself following how to build an acrylic box.

Tab-and-slot kit

Parts that slot together without glue, with a tray that lifts out for cleaning. It's a nice kit for classrooms and scout projects. Slots need to match the sheet's actual thickness, which varies; see tab-and-slot design.

Details that make a feeder work

  • Suction cup holes: most feeder suction cups have a mushroom-head stem that snaps into a 3/8 in. hole. Check yours and tell us the size. Place them near the top corners.
  • Drain holes: four to six 1/8 in. holes in the tray floor let rain out so seed doesn't rot.
  • A removable tray makes cleaning far easier. Clean feeders every couple of weeks to keep birds healthy.
  • A small roof or overhang keeps seed drier.
  • Engraved patterns or names on the back panel make it a gift. A light engraved pattern also makes the glass more visible to birds. See acrylic engraving.

Tip: suction cups hold best on clean, warm glass. Wipe the window with soapy water, dry it, and put the feeder up on a mild day. A drop of water on the cup helps it seal.

Keeping it clear

Wash with warm soapy water and a soft brush or cloth. Avoid bleach-strong solutions sitting on the plastic for a long time, and skip Windex-type window sprays and solvents on the acrylic parts; they can cause fine cracks called crazing. A dilute bleach rinse for disinfecting, followed by a thorough water rinse, is fine occasionally.

Have a feeder design? Upload your drawing, or describe what you want and we'll suggest the parts.

Questions

Will squirrels break an acrylic feeder?

They're more likely to pull it off the window than break it. A 1/8 in. feeder can take a squirrel's weight, but suction cups often can't. Mount feeders where squirrels can't jump to them.

Why does my window feeder fog up?

Condensation forms on the cold glass behind it, not usually on the acrylic. It clears on its own as the day warms up.