Purple Martin nest box
Published dimensions, a cut list for 1×12 (11 1/4 in.), and the placement rules that decide whether the brood survives. The entrance is 2–2 1/2 in. — cut it to the smaller figure if the range gives you a choice, because a hole bored oversize cannot be made smaller and lets European Starlings in.
Purple Martin
- Entrance hole 2–2 1/2 in.51–64 mm
- Hole above floor 1–2 in.25–51 mm
- Floor 6 × 6 in.152 × 152 mm
- Cavity depth 6 in.152 mm
- Mounting height 10–20 ft3–6.1 m
Habitat and placement: Wide open ground — at least 40 ft of clear air on all sides, ideally 30–120 ft from human housing and near water. Martins will not use housing hemmed in by trees.
Spacing between boxes: Colonial: compartments sit side by side in one house or gourd rack. Keep separate racks 30+ ft apart.
Predator guard: Pole baffle plus owl guards. A raccoon or a Great Horned Owl can empty a whole colony in one night.
When to install: Open the housing when scouts are expected in your area — February in the Gulf states, April in the northern states, later in Canada. Keep compartments closed until then so House Sparrows and starlings cannot claim them.
Notes: East of the Rockies, Purple Martins nest almost exclusively in human-supplied housing. Crescent-shaped entrances are widely used to exclude starlings while admitting martins. This is a commitment: unmanaged martin housing becomes a sparrow tenement.
Dimensions from: sialis.org spec compilation
No perch. Ever. A perch gives predators and House Sparrows a grip — cavity nesters do not need one.
Cut list
Every board you need, sized so the assembled box matches the published interior above. Pick your stock — the list updates.
1×12 (11 1/4 in.) · about 6 linear feet including waste
| Qty | Piece | Size | Notes |
|---|---|---|---|
| 1 | Floor | 6 × 6 in. | Trim about 1/4 in. off each corner for drainage. |
| 2 | Side | 6 × 8 1/4 in. | Bevel the top edge: 6 3/4 in. at the front rising to 8 1/4 in. at the back. |
| 1 | Back | 7 1/2 × 16 1/4 in. | Runs 4 in. above and 4 in. below the box for mounting screws. |
| 1 | Front | 7 1/2 × 6 3/4 in. | Bore a 2 in. hole, centred side to side, with its centre 2 3/4 in. up from the bottom edge. |
| 1 | Roof | 10 1/2 × 9 1/2 in. | Overhangs 3 in. at the front and 1 in. each side; butts against the back board. |
Before you cut
- Untreated wood, 3/4 in. thick. Cedar, cypress, or pine. Never pressure-treated, and never paint or stain the interior.
- Score the inside face below the entrance so nestlings can climb out. Smooth plywood traps them.
- Drainage and ventilation. Trim the floor corners; leave gaps or drill holes near the top.
- Make one side or the front open so you can monitor and clean between broods.
- Baffle on a smooth metal pole. This matters more than height, orientation, or anything else on this page.
When and where to put up a nest box — timing by region, habitat matching, orientation, and predator guards that actually work.
Other species
- American Robin open front
- Eastern Phoebe open front
- Eastern Bluebird 1 1/2–1 9/16 in.