Nest boxes provide important nesting habitat for many species of birds and mammals. When designing and building a nest box, one of the most important considerations is the type of wood used. The wood chosen affects the strength, durability, insulation, and even safety of the nest box. So what is the best wood to use? There are several factors to take into account when selecting wood for nest boxes.
Consider the Species
The species you hope will use the nest box should help guide the wood selection. Small songbirds like chickadees and wrens do well with thinner wood types around 3/4 inches thick. Larger species like wood ducks, screech owls, and American kestrels need thicker wood so the interior stays cool and provides more durability over years of use. Here’s a quick guide to recommended wood thickness based on the target species:
– Small songbirds (chickadees, nuthatches, titmice, wrens): 3/4 inches
– Bluebirds, tree swallows, house wrens: 3/4 – 1 inch
– Wood ducks: 1 1/8 – 1 1/4 inches
– Screech owls, kestrels: 1 1/4 inches or more
The entrance hole size should also match the species. Smaller holes around 1 – 1 1/2 inches are best for songbirds while larger owls and waterfowl need 2 – 3 inch holes. Wood duck boxes in particular should have oblong or oval holes at least 3 x 4 inches.
Choose Rot-Resistant Wood
Since nest boxes are exposed to the elements, moisture can quickly cause cheaper, low-density woods to rot. Using a rot-resistant wood ensures the nest box lasts for many years. Some of the best options include:
– Cedar – Has natural oils that resist decay and insects. Cedar is lightweight, easy to work with, and affordable.
– Redwood – Also contains natural oils. Redwood is extremely durable but more expensive than cedar.
– Cyprus – Similar durability and rot-resistance to cedar. The dense wood provides good insulation.
– Teak – A tropical hardwood that can last over a decade outdoors. The expense limits its use to high-end nest boxes.
Avoid low-cost woods like pine, fir, and spruce which decay quickly outdoors. Also avoid pressure-treated lumber which contains toxic chemicals.
Insulation Matters
Nest box walls should provide adequate insulation to maintain a stable internal temperature. Cavity nesting birds often choose nest sites based on this factor.
Woods like cypress and teak with their dense structure offer the best insulation. Cedar and redwood are also reasonably good insulators. Stay away from thin plywoods or woods like aspen which transfer heat rapidly.
You can also increase insulation by constructing nest boxes using two layers of wood with an air gap in between. Make sure to caulk all joints between the inner and outer layers.
Consider Hardness and Workability
Harder woods make more durable nest boxes that hold up better over time. But hardness can also make cutting and drilling more difficult.
Cedar offers a good balance of workability and durability. Hardwoods like oak and maple machine well but are prone to decay. Cypress and teak are extremely hard and need specialized tools.
Pine and other softwoods are easy to work with but compromised on longevity. Avoid super-hard exotic woods; nest boxes need to be affordable and practical for homeowners to construct.
Apply Protective Coatings
Applying stains or paints further increases the lifespan of nest boxes. Clear stains maintain the natural appearance while protecting from UV damage. Darker, opaque stains or paints provide additional insulation on hot days.
Be sure to use non-toxic polyurethane or acrylic wood finishes. Oil-based paints and stains emit harsh fumes. Follow the manufacturer instructions to ensure proper curing times before installing the nest box.
Here are some top coatings for nest boxes:
– Clear acrylic waterproofing sealant
– Clear semi-transparent penetrating wood stain
– Dark brown or green latex exterior paint
– Marine-grade spar varnish
Construct a Durable Roof
Even with rot-resistant wood, the roof is the most vulnerable part of a nest box. Getting wet repeatedly accelerates decay. Use rust-resistant hardware, design generous overhangs, and apply waterproof sealants along the roof.
Metal roofs provide the most weather protection. Screw galvanized sheet metal over a wooden roof using gasketed screws to prevent leaks. Aluminum flashing and copper work well too.
For wood roofs, opt for durable tongue & groove boards, or overlap individual boards like shingles. Apply acrylic caulk between boards to seal gaps. Use the same exterior paint/stain as the nest box walls.
Include Proper Ventilation
Proper air circulation keeps nest boxes from overheating while preventing condensation buildup inside. Drill ventilation holes near the roof that don’t compromise insulation but allow air exchange.
Small songbird boxes usually need just a few 1/4-1/2” holes. Larger owl and waterfowl boxes benefit from additional openings and screening to keep out drafts.
Placing the entrance hole higher on the front panel improves airflow. Leaving the floor unsealed also helps ventilate the box.
Choose Safe, Non-Toxic Materials
Avoid any chemical treatments and hardware that could harm birds or their offspring. Use hot-dipped galvanized or stainless steel screws and nails to avoid rust.
Do not use:
– Pressure treated wood
– Wood scrap with lead paint
– Steel wool for drainage holes
– Toxic stains and paints
When sourcing wood, verify it comes from sustainable forestry. Exotic tropical hardwoods in particular may not be eco-friendly.
Match the Location
Factor in where the nest box will hang when selecting wood. For example, a box on a sunny, south-facing tree needs insulation for heat resistance. An exposed site like a lakeshore or prairie will require maximum moisture protection and hardy fasteners.
Use thick, sturdy wood for boxes accessible to predators. Softwoods like pine quickly get chewed up by squirrels.
Metal predators guards can add defense but heavy-duty wood is the first line of defense.
Get the Right Thickness
We touched on recommended wood thickness earlier for different bird species. Getting this right for the target inhabitants is important.
Thinner walls make boxes easier for small species like chickadees to regulate temperature and grasp onto the entrance hole.
Larger owls and waterfowl need thicker wood to safely contain their weight and avoid interior damage. The thicker walls also provide better insulation.
Here are common wood dimensions to use based on species:
– Chickadees, titmice, wrens: 3/4 inches
– Bluebirds, tree swallows, house wrens: 3/4 – 1 inch
– Wood ducks: 1 1/8 – 1 1/4 inches
– Screech owls, kestrels: 1 1/4 inches or more
Use Proper Lumber Grade
For sturdy nest boxes, avoid thin or warped boards prone to cracking. Select lumber graded for appearance and durability:
– Cedar – Use grades from “Standard and Better” to “Clear”
– Redwood – “B Grade” or better
– Pine – “C-Select” or better
– Exterior plywood – Use at least CDX grade
Higher grades ensure straight boards free of knots, cracks, and defects. Knots in particular compromise insulation and can allow moisture intrusion.
Plywood grades reflect the durability of glues and veneers. Use marine-grade plywood for greatest moisture resistance.
Add Predator Protection
No wood is impervious to squirrels, raccoons, and snakes. beyond choosing durable wood, incorporate these defenses:
– Metal predator guard below entrance hole
– No perches to provide footing for predators
– Slick metal poles or baffles on mounting post
– Larger nest boxes difficult for most predators to enter
You can also use 1/2 inch mesh hardware cloth to completely wrap boxes, but make sure it does not obstruct ventilation.
Monitoring sites and promptly evicting problem wildlife helps too. Persistent predators may necessitate relocating the nest box.
Use Natural Weather Resistance
Some woods naturally resist decay and insect damage. Their innate durability comes from compounds within the living tree tissue.
Heartwood – The non-living inner wood is more decay resistant on species like cedar, cypress, and teak. Use all heartwood if possible.
Sapwood – The living outer wood is more susceptible to rot. Avoid using all sapwood.
Oils – Cedar and redwood contain natural oils that repel water and insects. Use lighter heartwood which has higher oil content.
Tannins – Found in oak, chestnut, and other species. Tannins protect against fungal decay and insects.
Waxes – Woods like Eastern red cedar contain waxes that waterproof the surface. Sawing exposes new wax-coated surfaces.
Extractives – Compounds that boost decay resistance in woods like redwood, osage orange, and black locust.
Add Supplemental Preservatives
Additional chemical treatments can extend the service life, but avoid toxic options. Common wood preservatives include:
Borates – Borate powder or sodium octaborate solutions protect against rot, fungi, and insects. Low toxicity makes them safe for bird boxes.
Oils – food-grade oils like paraffin and linseed oil boost water resistance but require frequent reapplication. Avoid mineral oil which can harm feathers.
Wood stabilizers – Mixed with water, these compounds fortify wood structure against moisture and decay. Examples are ACQ-10 and Tim-Bor.
Natural oils – Options like tung oil and boiled linseed oil penetrate deeply to protect wood. Follow manufacturer safety precautions.
Choose preservatives compatible with any exterior paint or stain coats. Never use creosote, pentachlorophenol, or other commercial wood preservatives.
Use Reinforcing Fasteners
High-quality galvanized screws and ringed nails provide extra reinforcement and longevity. Choose stainless steel hardware for ocean and lakeshore locations.
Screw shank diameter should be no wider than 80% of the receiving board’s thickness to avoid cracking. Predrill holes to prevent splitting.
Use the following fastener guidelines:
– Walls – 2” galvanized deck screws
– Roof – 2” stainless steel screws with washers
– Hinges – 3” galvanized screws
– Mounting – 3/8” x 5” lag screws with washers
For large duck boxes, incorporate threaded rods, bolts, corner brackets, or metal joints for structural strength. Avoid non-rated particleboard screws.
Add Proper Construction Details
Following best practices for box joinery and finishing also contributes to a long-lasting nest box:
– Recess exterior screw/nail heads for water resistance
– Drill pilot holes and countersink screws to prevent splitting
– Use galvanized framing anchors at all joints for rigidity
– Caulk wall joints with non-toxic acrylic caulk before painting
– Construct overhangs for rain protection along roof edges
– Seal external wood end grain with waterproof glue or epoxy
Choose durable hinges like strap hinges or rust-resistant piano hinges. Apply exterior-grade wood glue formulated for weather resistance.
Use Reinforcing Materials
Metal hardware cloth, roofing, flashing, and fasteners bolster wood nest boxes. You can also incorporate these reinforcements:
– Wire mesh lining – Protects interior walls from damage
– Metal corners – Wraps corners for strength and prevents chewing
– Aluminum thresholds – Improves durability along bottom entrance
– Composite panels – Provides insulation along problematic moisture areas
– Plexiglass viewing windows – Offers visibility without compromising structure
Any added materials should be non-toxic and not obstruct ventilation. Avoid lead, zinc, or copper flashing.
Go Beyond Wood
While traditional, all-wood nest boxes work well, some alternatives provide added benefits:
Composite Boxes – Made from recycled wood/plastic materials. Resists moisture and chewing predators. Has insulation value of wood but requires plastic construction skills.
Poly Lumber Boxes – Polyethylene plastic lumber is rot-proof and never needs painting. Insulates well and makes clean, easy-to-construct boxes. Can feel slippery to birds.
Concrete Boxes – Extremely durable and well-insulated but difficult to modify. Requires sealing small pores that could absorb water. Heavier than wood.
PVC Pipe Boxes – Readily available drainage pipe makes cheap, indestructible nest boxes. Use larger diameter pipe in hot climates for temperature control. Seal open ends well.
Choose Sustainable Sources
Verify any purchased lumber comes from responsibly managed forests. Materials should be Forest Stewardship Council (FSC) certified or equivalent.
Reclaimed, reused, or recycled wood is ideal. Avoid threatened species like Brazilian mahogany or Spanish cedar. Regional woods reduce transport impacts.
Never use lumber with chemical treatments, lead paint, or other toxic residues. Avoid finishing nest boxes with hazardous stains or paints.
Building DIY boxes from unverified wood scrap is risky. Trace material sources or opt for new lumber from a trusted supplier.
Prioritize Safety
Follow standard safety practices when working with power tools to construct nest boxes:
– Use sharp blades, drill bits, and router bits
– Secure workpieces with clamps before machining
– Wear safety goggles, respirator, and hearing protection
– Unplug tools before changing blades or bits
– Keep your work area clean and well lit
Take precautions when working with pressure treated, tropical, or reclaimed wood which may contain toxic residues. Wear gloves and a dust mask.
Check boxes frequently and replace hazardous, damaged, or deteriorated components that could harm wildlife.
In Summary
Choosing the right lumber is key to constructing durable, safe nest boxes that get used year after year by desirable wildlife. Use these wood selection principles:
– Match the species in terms of insulation, hardness, and entrance size
– Look for natural decay resistance and waterproof traits
– Start with premium grade, knot-free lumber in the proper thickness
– Use non-toxic weatherproof finishes and hardware
– Incorporate metal or composite reinforcements at vulnerable points
– Ensure proper ventilation but not draftiness
– Favor sustainable, regional wood sources to reduce environmental impacts
– Prioritize wildlife health through safe materials and design
Following these guidelines for selecting lumber will lead to quality nest boxes that provide shelter for native birds and mammals in your area. Partnering appropriate wood with protective finishes and detailing yields an end product that withstands weather and wear while keeping inhabitants safe. Whether you construct nest boxes for your own property or to contribute to conservation projects in your community, put these wood selection principles into practice so each one built makes a lasting impact.