Determining the Right Birdhouse Dimensions and Sizes

Cavity-nesting birds are flexible in their requirements for the preferred size of a birdhouse, but there is more than species preference at stake when planning the right birdhouse dimensions. Whether you are building a birdhouse or choosing a new one to purchase, the right dimensions and sizes can make all the difference in making safe, comfortable housing for your backyard birds.

Why Birdhouse Sizes Matter

Birds instinctively look for nesting cavities and birdhouses that are the right size for their needs, but what determines that best size? Many factors affect what size home birds need, including:

• Adult Size: The birdhouse needs to be large enough to be comfortable for the brooding adults and still provide adequate circulation and ventilation. In addition to interior dimensions, the birdhouse entrance hole size needs to have enough space for the movements of the adult birds as they bring food back and forth to their mates and chicks. A house that is too tight can affect the adults' feathers and make them more vulnerable to predators and poor weather.
• Brood Size: The more eggs a bird typically lays, the larger a base the birdhouse will need to fit each egg safely and comfortably, with room for the eggs to be rearranged if needed for proper incubation. Species that only lay a few eggs may use smaller houses, while birds that have larger broods will need houses with larger bases.
• Fledgling Size: Altricial baby birds, such as most songbirds, can be nearly the size of adults by the time they leave the nest and will need a bigger house to accommodate their growth. Precocial birds, like cavity-nesting waterfowl, however, leave the nest much sooner and will not be as large, so a smaller house size can be acceptable.
• Safety: The size of a birdhouse directly impacts how safe the house is for both the parents and their chicks. The house must be large enough to accommodate all its residents with proper ventilation for air circulation and temperature control, and the entrance must be positioned at an appropriate distance above the floor to safeguard against predator intrusion. At the same time, a house that is too large may not retain enough heat for healthy eggs and chicks. A larger house could more easily admit birdhouse predators or other unwanted guests as well, and too much room will not help the chicks feel snug and secure.
• Local Resources: Even if a birdhouse is not the best possible size, birds may still take up residence if the area has abundant food, is safe from predators, and features a good water source. Those resources are critical for raising baby birds successfully, and adult birds will only choose houses in the best possible location, even if the house is not perfectly ideal.

Planning the Best Birdhouse Dimensions

When measuring a birdhouse for the proper dimensions, be sure to take into account the thickness of the walls, floor, and ceiling. The dimensions for a safe, comfortable birdhouse are interior measurements, and improper measuring could subtract as much as two inches or more from the overall size of the house, making it much too small to be attractive and useful to the birds.

See the table below for the proper interior base, overall interior height, and entrance height measurements for the most common and desirable birds that use birdhouses.

Ideal Birdhouse Dimensions (Inches)

Beyond the Measurements

While the right birdhouse measurements are essential, they are not the only factor that will encourage birds to use the house. When choosing or building a birdhouse, don't forget to consider:

• Where to mount the birdhouse
• The best time to put up the birdhouse
• Appropriate habitat for the desired birds
• Bird feeders, birdbaths, and other ways to attract birds
• Nesting material availability
• Cleaning the birdhouse when necessary

With proper measurements and careful consideration of what makes a house attractive to birds, it is possible to offer the perfect housing for your backyard birds to raise their families.