Nest Box & Bird Feeder Guide
Nest box hole sizes by species — the dimension that decides who moves in — plus which seed attracts what and what to avoid.
The hole size is not a detail
Entrance diameter is the single most important dimension on a nest box, because it selects who can get in. Build it a quarter-inch too large and you have not built a more welcoming box — you have built one that a bigger, more aggressive species will take.
The specific line is 1.5 inches. At or below it, European Starlings cannot enter. Above it, they can — and starlings are non-native, will evict occupants, and will kill nestlings and adults to take a cavity. A bluebird box drilled to 1¾ inches because that was the bit in the drawer is worse than no box at all.
Nest box dimensions
| Species | Hole | Floor | Height | Notes |
|---|---|---|---|---|
| House Wren | 1.125″ | 4×4″ | 5–10 ft | Will happily use a small box in a shrubby garden. A 1⅛ inch hole keeps out almost everything larger. |
| Black-capped Chickadee | 1.125″ | 4×4″ | 5–15 ft | Add a few centimetres of wood shavings to the floor — chickadees excavate, and an empty box reads as unfinished. |
| Tufted Titmouse | 1.25″ | 4×4″ | 5–15 ft | Similar to chickadees but wants slightly more room and a slightly larger hole. |
| White-breasted Nuthatch | 1.25″ | 4×4″ | 12–20 ft | Prefers a box mounted higher and on a mature tree rather than a post. |
| Downy Woodpecker | 1.25″ | 4×4″ | 12–20 ft | Fill the box with wood shavings. Woodpeckers want to excavate a cavity, not move into one. |
| Eastern Bluebird | 1.5″ | 5×5″ | 4–6 ft | Exactly 1½ inches, and it matters — larger admits starlings, which will kill the nestlings. Mount on a smooth pole with a baffle, facing open ground. |
| Tree Swallow | 1.5″ | 5×5″ | 5–15 ft | Same box as a bluebird. Pairing two boxes 5 to 20 feet apart lets both species nest, since swallows tolerate bluebirds but not other swallows. |
| Purple Martin | 2.125″ | 6×6″ | 12–20 ft | Colonial, so they want a multi-compartment house in the open, well away from trees. The eastern population nests almost entirely in human-provided housing. |
| Northern Flicker | 2.5″ | 7×7″ | 6–20 ft | Pack the box solid with wood shavings; flickers excavate their own cavity and will reject an empty one. |
| Eastern Screech-Owl | 3″ | 8×8″ | 10–30 ft | Add shavings and site it at a woodland edge. Often used by squirrels first, which is not a failure. |
| Wood Duck | 4″ | 10×10″ | 6–30 ft | An oval hole about 3 by 4 inches, deep box, shavings inside, and a ladder of mesh below the hole so ducklings can climb out. |
Green holes exclude starlings; orange ones do not, and those boxes need active monitoring.
What to put out
| Seed | Attracts | Feeder | Notes |
|---|---|---|---|
| Black oil sunflower | Almost everything — finches, chickadees, nuthatches, cardinals, jays, woodpeckers | Tube, hopper or platform | If you put out one seed, put out this one. Thin shells, high fat, and eaten by a wider range of species than anything else. |
| Nyjer (thistle) | Goldfinches, siskins, redpolls | Fine-mesh or nyjer tube | Very small seed for very small bills. Goes stale quickly and birds will simply ignore old nyjer, so buy small quantities. |
| Safflower | Cardinals, chickadees, titmice, house finches | Hopper or platform | The squirrel and grackle answer. Both usually dislike the bitter taste, while cardinals take it readily. |
| White proso millet | Juncos, sparrows, doves, towhees | Ground or low platform | For the birds that feed on the floor. Scatter it rather than hanging it, and only as much as gets eaten in a day. |
| Peanuts (shelled) | Jays, woodpeckers, titmice, nuthatches | Mesh peanut feeder | High energy and popular. Keep it dry — damp peanuts grow moulds that are genuinely dangerous to birds. |
| Suet | Woodpeckers, nuthatches, wrens, chickadees | Suet cage | Cold-weather food. Use no-melt dough in warm weather, since rendered fat goes rancid and can foul feathers. |
| Cracked corn | Doves, jays, sparrows, quail | Ground | Cheap and effective, and also the seed most likely to bring in starlings, grackles, rodents and deer. Use sparingly. |
| ⚠ Milo and red millet | Very little in most regions | — | The filler that bulks out cheap seed mixes. Most birds throw it on the floor, where it rots and attracts rodents — which is why a cheap mix is rarely cheap. |
If you buy one bag, buy black oil sunflower
Thin shells that small bills can open, high fat content, and eaten by a wider range of species than anything else you can put out. Almost every feeder bird in North America takes it, which is not true of any other single seed.
The corollary is to avoid cheap mixes. They are bulked out with milo and red millet, which most birds in most regions simply throw on the ground — where it rots and attracts rodents. A bag that looks half the price is frequently more expensive per seed actually eaten.
Running a feeder responsibly
- Clean feeders every two weeks, and more often in warm or wet weather. Dirty feeders spread salmonellosis, conjunctivitis and trichomoniasis, and a neglected feeder does more harm than no feeder at all.
- Take feeders down entirely if you see sick birds — lethargic, fluffed up, reluctant to fly. Two weeks down and thoroughly cleaned is the standard advice for breaking transmission.
- Site feeders either within about three feet of a window or more than thirty feet away. The lethal zone is in between, where birds build up enough speed to be killed by the strike.
- Cover matters as much as food. A shrub or brush pile within a few metres gives birds somewhere to escape to, and a feeder in the open middle of a lawn gets far less use.
- Water is used by more species than any seed, including birds that never visit a feeder. A shallow dish kept clean and ice-free outperforms most feeders.
How to use
- Pick the species you hope to attract.
- Match the entrance hole diameter exactly.
- Mount at the right height with the correct exposure.
- Clean the box out between seasons.
Frequently asked questions
Why does the entrance hole size matter so much?
Because it decides who can get in, and that is the main control you have. A hole sized for a chickadee excludes larger competitors; a hole a little too large lets in house sparrows and starlings, which are aggressive cavity competitors and will evict or kill the birds you wanted.
What sizes suit which birds?
Roughly: around an inch and an eighth for wrens and chickadees, an inch and a half for bluebirds, and larger for flickers and screech owls. Getting it right to the sixteenth of an inch genuinely matters — this is the one measurement not to approximate.
Should the box have a perch?
No, and this is the most common mistake in bought boxes. Cavity-nesting birds do not need one, and a perch gives predators and competing species something to grip while raiding the nest. Boxes sold with perches are designed for shops rather than birds.
Which seed attracts the most species?
Black oil sunflower, by a wide margin — high in fat, thin-shelled, and eaten by most feeder birds. Nyjer draws finches, and white millet suits ground feeders. Cheap mixes padded with red milo are mostly wasted, since few birds eat it and it ends up on the ground.
Is feeding birds actually good for them?
On balance, when done well. Clean feeders and appropriate food genuinely help through hard weather. Neglected feeders spread disease — salmonellosis and conjunctivitis both spread at feeders — so regular cleaning is part of the responsibility rather than an optional extra.
What about cats?
They are the single largest human-related cause of bird deaths in many countries, killing enormous numbers annually. Placing feeders away from cover a cat can stalk from, and keeping cats indoors or supervised, does more for garden birds than any feeder choice.
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