Great Horned Owls are one of the most common owls found across North America. These large, powerful owls are known for their deep hooting calls and fierce hunting abilities. When it comes to nesting, Great Horned Owls do not build their own nests. Instead, they rely on nests built by other large birds or nesting boxes provided by humans.
If you want to attract Great Horned Owls to your property, providing an artificial nesting box is a great way to do it. However, it’s important that the nest box is appropriately sized for the owls. An owl box that is too small or too big will not be used. So how big should a Great Horned Owl nest box be?
Average Dimensions of a Great Horned Owl
To determine the proper size for a Great Horned Owl nest box, it’s helpful to understand the average dimensions of these large owls:
- Length: 18-25 inches
- Wingspan: 40-60 inches
- Weight: 3-4 pounds
The female owl is generally larger than the male. But even the male Great Horned Owl is an impressively large bird.
Inside Dimensions of the Box
For the interior cavity of the nest box, the recommended dimensions are:
- Depth: 15-18 inches deep
- Width: 14-20 inches wide
- Height: 16-24 inches tall
This provides enough room for the adult owls to roost comfortably inside and gives them space to raise young. The interior of the box should be deep enough so the owls can’t see out the opening from the back wall. But it shouldn’t be so deep that they can’t access the entrance.
Entrance Hole Size
The entrance hole is one of the most important features of an owl nest box. Great Horned Owls need an oval-shaped opening about 10 inches high x 6 inches wide. This allows the adults to easily enter and exit while keeping predators out.
It’s crucial that the entrance hole is appropriately sized. An entrance hole that is too large may allow raccoons or other animals access to the nest. A hole that is too small may prevent the adult owls from entering.
Height of the Box
Mounting the owl box at the proper height is also key. It should be installed:
- 15-30 feet above the ground
- At least 100 feet away from trees or other perches (to deter predators)
The box can be placed on a pole specifically installed for the nest box, or mounted to the side of a barn or tall tree.
Materials for Great Horned Owl Nest Boxes
Great Horned Owl boxes can be made from a variety of solid and durable materials including:
- Wood (pine, cedar, plywood)
- Composite lumber
- Plastic
- Fiberglass
The interior of the box should be sanded or roughened to allow the owls to grip the surface when entering the nest. Applying non-toxic stain or sealant to the exterior can help the box withstand weathering.
It’s also a good idea to include ventilation holes near the top of the box as well as wood shavings, sawdust or pine straw inside the box for nesting material.
Example Materials
| Material | Pros | Cons |
|---|---|---|
| Plywood | Easy to work with, durable | Prone to warping |
| Cedar | Naturally rot resistant | More expensive |
| Plastic | Long lasting | Can crack over time |
Cleaning and Maintenance
It’s important to clean out old nesting material in the box after each nesting season. Be sure to wear gloves and a mask when cleaning out old material to avoid inhaling dust or particles that could carry disease.
The box should be cleaned out by late winter before breeding season gets underway. Simply remove all old nesting debris, scrape out any caked materials, and apply fresh wood shavings or pine straw.
Regular cleaning will help encourage Great Horned Owls to reuse the box year after year. Discouraging other species like European Starlings from using the box will also help keep it clean and owl-friendly.
Conclusion
Providing an appropriate nesting box is a great way to attract Great Horned Owls to your property. By following the recommendations for interior dimensions, entrance hole size, mounting height, and materials, you can create an attractive nesting site that these magnificent owls will return to each breeding season.
A Great Horned Owl box with interior dimensions around 15-24 inches deep x 14-20 inches wide x 16-24 inches high is ideal. With a 10 x 6 inch oval entrance hole mounted 15-30 feet high, you are providing a safe and appealing cavity for these owls to raise their young.
Constructing a sturdy owl box from wood, plastic or composite materials and properly maintaining it will result in years of owl nesting activity for you to observe and enjoy!
