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To Fill or Not to Fill: An Expert Guide on What to Put Inside a Birdhouse

A welcoming birdhouse in your backyard can be a source of immense joy, offering a front-row seat to the wonders of nature as avian families move in and raise their young. A common question that enthusiasts and new birdwatchers ask is, “What should I put inside a birdhouse to make it more attractive and comfortable for the birds?” The answer, surprisingly to many, is almost always nothing at all. This guide will delve into the expert recommendations on preparing a birdhouse for its feathered occupants, exploring what materials to provide (and what to avoid), and how to create a safe and inviting haven for nesting birds.

The Golden Rule: Let the Birds Decorate

For the vast majority of common backyard birds that use nest boxes—such as wrens, chickadees, bluebirds, and tree swallows—the best practice is to leave the birdhouse empty. These birds are instinctively driven to seek out and arrange their own nesting materials. This process is a crucial part of their breeding and courtship rituals. Filling a birdhouse with material, no matter how well-intentioned, can actually deter these birds from using it. They may perceive the box as already occupied or the materials as unsuitable for their specific needs.

An empty birdhouse allows the birds to customize their nest according to their species-specific habits. They will meticulously select and place materials to create a nest that is the right size, shape, and insulation for their eggs and young.

Why You Shouldn’t Add Birdseed

A common misconception is that placing birdseed inside a birdhouse will attract birds. This is a myth that can have dangerous consequences. Birdhouses are for nesting, not feeding. Adding birdseed or any other food to a birdhouse can:

Attract predators: The scent of seeds can lure squirrels, raccoons, snakes, and even predatory insects into the birdhouse, endangering the eggs and nestlings.
Promote disease: Leftover seed can become moldy and harbor bacteria in the enclosed space of a birdhouse, creating an unhealthy environment for the birds.
Confuse the birds: A birdhouse with food in it is not a suitable nursery. Birds instinctively know this and will likely avoid a box that smells of potential decay and predators.

Keep your bird feeders and birdhouses separate. The Cornell Lab of Ornithology recommends placing feeders at a distance from nest boxes to prevent these issues.

Offering a Helping Hand: Safe Nesting Materials to Provide Near the Birdhouse

While you shouldn’t fill the birdhouse itself, you can certainly help the birds with their construction efforts by providing a selection of safe nesting materials in your yard. This can be a delightful way to watch them gather supplies. Create a small, designated area or use a clean suet cage to offer these materials.

Safe and Recommended Nesting Materials:

Twigs and Small Sticks: Many birds use these as the foundation for their nests.
Dried Grass and Leaves: Offer a pile of untreated grass clippings and fallen leaves. Ensure they are dry to prevent mold.
Pine Needles: A favorite of many species, including bluebirds.
Moss and Lichen: These provide excellent camouflage and insulation.
Feathers: A soft lining for the nest. You can purchase these from craft stores, but ensure they are clean and natural.
Natural Cotton or Wool: If you offer these, it is crucial to cut them into short pieces, no longer than an inch. Long strings can be a significant hazard.
Coconut Fiber: Often sold as “pet-safe” bedding, this is another excellent natural material.
Mud: A patch of mud in your garden can be invaluable for birds like robins and swallows, who use it as a cement for their nests.

When providing these materials, ensure they are free from pesticides and other chemicals. A natural, slightly “messy” yard is often the best source of nesting materials for birds.

A Word of Caution: What NOT to Put in a Birdhouse or Your Yard

Just as important as knowing what to provide is understanding what can be harmful to birds. Certain materials, some of which may seem soft and suitable, can pose a serious threat to nestlings and adult birds.

Unsafe and Harmful Materials:

Dryer Lint: This is a commonly cited “no-no” from experts like the National Audubon Society. While it may seem soft, dryer lint is composed of synthetic fibers that can lose their structure when wet and do not provide good insulation. It can also contain harmful chemicals from detergents and fabric softeners.
Human Hair and Pet Fur: Long strands of hair can easily entangle the delicate legs and wings of baby birds, leading to injury or even amputation. Pet fur, especially from animals treated with flea and tick medications, can be toxic to birds.
Yarn, String, and Fishing Line: Similar to hair, these can create a deadly entanglement hazard. If you must offer yarn or string, cut it into very short pieces.
Plastic Strips, Tinsel, and Cellophane: These are unnatural materials that can be ingested or cause entanglement. They do not break down and contribute to environmental pollution.
Synthetic Fibers: Materials like polyester and nylon do not breathe well and can retain too much moisture, chilling the eggs and nestlings.

Exceptions to the Rule: When to Add Material to a Birdhouse

There are a few specific instances where adding a shallow layer of a particular material is recommended. This is primarily for birds that do not build intricate nests and instead rely on pre-existing cavities.

Woodpeckers, Owls, and Kestrels: These larger cavity-nesting birds do not typically bring in large amounts of nesting material. For these species, it is recommended to add a 2- to 3-inch layer of wood shavings (not sawdust) to the bottom of the birdhouse. This provides a soft cushion for the eggs and helps to keep them from rolling around. Never use sawdust, as it can retain moisture and clump together when wet.
Wood Ducks: These waterfowl also benefit from a deep layer of wood shavings in their nest boxes.

When in doubt, research the specific bird species you are hoping to attract to your birdhouse to understand their unique nesting requirements.

Preparing Your Birdhouse for Nesting Season

Beyond the question of what to put inside, proper preparation and maintenance are key to attracting birds and ensuring their safety.

Annual Cleaning is a Must

At the end of the breeding season, typically in the fall, it is crucial to clean out your birdhouse. Old nests can harbor parasites, mites, and bacteria that can harm the next occupants.

Remove the old nest: Wear gloves and carefully remove all nesting material.
Scrub the interior: Use a solution of one part bleach to nine parts water to scrub the inside of the box. A stiff brush will help remove any debris.
Rinse thoroughly: Rinse the box completely with clean water to remove any bleach residue.
Dry completely: Allow the birdhouse to air dry thoroughly in the sun before storing it or putting it back up for the winter.

Prime Placement for Success

Where you place your birdhouse is as important as its contents. Here are some general guidelines:

Height: The ideal height varies by species, but a general range is 5 to 15 feet off the ground.
Orientation: Face the entrance hole away from prevailing winds, typically east. This protects the nest from cold winds and driving rain.
Location: Mount the birdhouse on a pole or a tree in a relatively open area, but with some nearby cover like shrubs or trees for the birds to perch on. Avoid placing it in deep shade.
Predator Protection: Install a predator guard on the mounting pole to prevent raccoons, snakes, and cats from reaching the nest box.
Avoid Perches: Birdhouses with perches below the entrance hole can actually help predators gain access to the nest. Cavity-nesting birds do not need them.

Conclusion: Simplicity is Key

The desire to create a welcoming home for birds is commendable. However, when it comes to what to put inside a birdhouse, the best approach is usually the simplest: leave it empty. By providing a clean, well-placed birdhouse and offering a selection of safe, natural nesting materials nearby, you are creating the ideal environment for your feathered neighbors to thrive. Resisting the urge to “decorate” the interior of the birdhouse allows birds to follow their natural instincts, leading to a more successful and rewarding nesting season for both you and them. Happy birdwatching!