Published on September 18, 2026 • Last Updated on September 20, 2026
For most standard backyard birdhouses, you should leave the inside empty and let the birds bring their own nesting material. Many cavity-nesting songbirds build their own nest once they accept the box.
There are important exceptions. Some species that naturally nest on wood chips, debris, or bare cavity floors can benefit from a layer of untreated wood shavings in a nest box. Wood Ducks and several owl species are good examples.
The safest rule is therefore not “always add bedding” or “never add bedding.” It is: follow a nest-box plan for the species you are trying to attract.
The quick answer by type of bird
| Bird or box type | What to put inside |
|---|---|
| Typical small backyard songbird box | Usually leave it empty and let the birds build the nest |
| Black-capped or Chestnut-backed Chickadee box | A shallow layer of wood shavings may be used |
| Carolina Chickadee box | Wood chips are not necessary |
| Eastern Screech-Owl box | About 2–3 inches of wood shavings |
| Wood Duck box | About 4 inches of wood shavings |
| Barn Owl box | No added material is required; a shallow layer of wood shavings is optional |
These examples show why species matters more than a universal birdhouse rule. Cornell NestWatch gives different box instructions for different cavity nesters rather than recommending one bedding setup for every bird.
Why most birdhouses should start empty
Most birds that construct a nest want to gather and arrange the material themselves. Texas Parks and Wildlife advises against putting nesting material inside a typical birdhouse to encourage occupancy, noting that many birds are selective about the materials they use and how they arrange them.
An empty box also avoids guessing which material a particular species wants. A wren, chickadee, bluebird, owl and duck do not all use a cavity in the same way.
Instead of trying to furnish a generic birdhouse, first identify the species the box is designed for. Entrance size is one of the easiest clues. Our Birdhouse Hole Size Guide explains why different cavity nesters require different entrance dimensions.
Birdhouse bedding and nesting material are not the same thing
It helps to separate two different ideas:
- Material placed inside the nest box before birds arrive, such as wood shavings.
- Nesting material made available nearby so birds can choose it and carry it to the nest themselves.
Those are not interchangeable.
Cornell’s All About Birds notes that birds may collect materials such as dead twigs, leaves, untreated dry grass, plant fibers, moss, bark strips and pine needles. Leaving natural materials available in a yard can therefore help nest-building birds without filling the birdhouse for them.
When wood shavings belong inside a nest box
Some cavity nesters do not build the kind of structured nest people usually imagine. For those species, the substrate on the floor of the cavity can matter.
Wood Ducks
Cornell NestWatch recommends placing about 4 inches of wood shavings on the floor of a Wood Duck nest box.
Wood Duck boxes are large, specialized structures and should not be treated like ordinary backyard songbird houses. Cornell also recommends replacing the old nesting material with fresh shavings after a completed brood when preparing the box for another nesting attempt.
Eastern Screech-Owls
For Eastern Screech-Owls, NestWatch recommends 2–3 inches of wood shavings in the bottom of the box.
Other owl species can have their own requirements, so do not copy that depth automatically into every owl box.
Barn Owls
Barn Owls are a useful example of why the answer is not always simple. NestWatch says it is not necessary to add material after cleaning because Barn Owls can create a nesting substrate from shredded pellets. However, a shallow layer of roughly 3/4 inch of wood shavings may be added.
Some chickadees
Cornell’s nest-box placement guidance says about 1 inch of wood shavings can be placed in boxes for Black-capped and Chestnut-backed Chickadees.
But even closely related species can differ. The same NestWatch guidance notes that Carolina Chickadees do not do much excavating and that wood chips are not necessary for them.
That is another reason to follow the plan for the target species rather than using one rule for all chickadees—or all birdhouses.
What kind of wood shavings should you use?
If a species-specific nest-box plan calls for shavings, use plain, untreated wood material rather than scented, chemically treated or synthetic bedding.
The purpose is to reproduce the loose wood debris or substrate that may be present in a natural cavity—not to create a soft pet-style bed.
Follow the depth and material recommendation in the species-specific plan instead of filling the box generously. Some cavity nesters may remove excess material themselves.
What should you avoid putting in a birdhouse?
Do not assume that something soft is automatically safe for nesting birds.
Cornell and Audubon both caution against several commonly offered materials. In particular, avoid materials that can break down badly when wet, contain chemicals or create entanglement hazards.
- Dryer lint
- Plastic strips
- Tinsel
- Cellophane
- Other synthetic or potentially hazardous fibers
Pet fur also deserves caution. Cornell notes that fur from pets treated with flea or tick products should not be offered, and very fine fur can absorb water.
A better way to help nest-building birds
If you want to help birds that build their own nests, improving the surrounding habitat is usually more useful than stuffing material into the box.
Natural materials such as leaves, twigs, untreated grass, moss, bark and plant fibers can be left available in the yard. Birds can then select the material that fits their own nesting behavior.
This also helps birds that do not use birdhouses at all.
What if there is already an old nest inside?
An old nest is different from intentionally adding new nesting material.
Do not remove or modify material while a nest is active. If eggs, nestlings or active adults are present—or you are unsure whether the nesting attempt has finished—leave the box alone.
Once a nesting attempt is clearly over, maintenance depends on the species and season. Some nest-box programs recommend removing old material, while certain species-specific setups call for replacing substrate such as wood shavings before the next nesting attempt.
The simplest rule to remember
Leave an ordinary birdhouse empty unless the nest-box plan for the target species specifically tells you to add something.
For many backyard songbirds, the birds will build the nest themselves. For cavity nesters such as Wood Ducks and some owls, wood shavings may be an intentional part of the box setup.
The species-specific plan should always win over a generic birdhouse rule.
Frequently Asked Questions
Should I put grass or straw inside a birdhouse?
Usually not. For a standard songbird nest box, leave the cavity empty and allow the birds to gather and arrange their own material unless a species-specific plan says otherwise.
Should I put sawdust in a birdhouse?
Do not add sawdust to a generic birdhouse simply because it seems soft. When a nest-box plan calls for substrate, it commonly specifies wood shavings or chips and gives an appropriate depth for that species.
Do bluebird houses need nesting material?
Do not pre-build a nest or fill a standard bluebird box with bedding. Let the birds construct the nest themselves and use a nest-box design intended for bluebirds.
Can I add nesting material after birds have started using the box?
Avoid altering an active nest box. Once birds are nesting, unnecessary disturbance can interfere with the nesting attempt. Make setup changes when the box is inactive and follow the guidance for the target species.
Sources & Further Reading
- Cornell NestWatch — Nest Box Placement
- Cornell NestWatch — Wood Duck Nest Box Guidance
- Cornell NestWatch — Eastern Screech-Owl Nest Box Guidance
- Cornell NestWatch — Barn Owl Nest Box Guidance
- Texas Parks & Wildlife — Bird Houses
- Cornell Lab — Providing Nest Material for Birds: Dos & Don’ts
- Audubon — What Nesting Materials Are Safe for Birds?
Jonathan Gron is the founder and editor of OwlRatings, where he researches birding, backyard wildlife and practical bird-safety guidance using current primary, government and professional sources.
