Purple martins are a popular species of swallow that many homeowners enjoy having around their property. These aerial acrobats put on dazzling displays as they swoop and dive to catch insects. One of the best ways to attract purple martins is to install a custom-made purple martin house.
Why Do Purple Martins Use Birdhouses?
Purple martins are dependent on cavities for nesting and roosting. However, due to habitat loss and competition from introduced species like European starlings and house sparrows, it can be challenging for purple martins to find suitable natural cavities.
Artificial nest boxes allow you to provide habitat specifically for purple martins. Properly constructed and placed martin houses can help establish new martin colonies or expand existing ones. Offering housing for these beneficial birds will allow you to enjoy their graceful flight and energetic chattering close to home.
Choosing the Right House Design
There are a few key factors to consider when selecting or building a purple martin house:
- Multiple compartments – Houses should have at least 6-12 individual nesting cavities. Purple martins are colonial nesters and prefer to nest in groups.
- Ventilation – Nests need airflow to prevent overheating and the growth of parasites. Holes, spacing between compartments, and overhangs provide ventilation.
- Easy access – Convenient access to monitoring and maintenance helps keep birds healthy.
- Durability – Martin houses should be made of weather-resistant materials like aluminum, stainless steel, resinated wood, or PVC.
- Predator guards – Guards prevent access to nests by predators and competitors.
There are many high quality ready-made martin house options available from reputable bird product retailers. Alternatively, you can build your own following an approved house plan.
Determining the Right Nest Entrance Hole Size
One of the most important design factors in a purple martin house is the size of the entrance holes leading into each nesting cavity.
Purple martins prefer a circular entrance hole that is:
- 2 1/8 inches to 2 3/8 inches in diameter
A hole in this size range allows adult purple martins to easily enter and leave the nest, while excluding larger birds like starlings.
The hole size should not be increased. Although it may seem counterintuitive, enlarging the holes does not help purple martins and actually harms them by allowing access to predators and competitors.
Why the Hole Size Matters
There are several reasons why the nest entrance hole must be precisely the right diameter:
- Keeps out larger species – The 2 1/8 to 2 3/8 inch hole is tailored specifically to purple martins. Larger openings allow European starlings, house sparrows, and other invasive species to take over martin houses.
- Discourages owls – Screech owls and other small owl species can enter and prey on nestlings in cavities with holes larger than 2 1/4 inches.
- Prevents overheating – Starlings tend to tightly pack their nests into compartments, causing dangerous overheating in hot summer weather. The smaller purple martin entrance holes help prevent starlings from usurping cavities.
- Easy for monitoring – A hole sized for adult martins allows you to inspect nests by plugging the hole with your finger.
In rare cases, a hole slightly smaller than 2 1/8 inches may be appropriate if you are in an area with American sparrows or house wrens competing for sites. Consult with your local purple martin landlord club for guidance.
Installing the Entrance Holes
For purpose-built martin houses, the entrance holes should be an integral part of the nest compartment. This provides the most durability and security.
If modifying an existing structure, carefully measure and cut holes to meet the recommended specifications. Use a hole saw bit with the appropriate diameter. Hole placement will vary based on house design and can be determined with guidance from martin housing plans.
Make sure entrance holes are smooth with no rough edges. Rough edges can injure martins entering or exiting the hole. A drill bit slightly smaller than the hole saw can be used to smooth rough edges.
Entrance holes should not be angled upward. Horizontal or downward sloping holes are best to prevent rain from entering the nest.
Once the holes are cut, the interior of the holes should be painted black or a dark color. This helps attract martins to the cavities.
Maintaining the Hole Size
It is important to ensure the hole size does not increase over time. As mentioned above, enlarging holes to more than 2 1/4 inches can allow problematic species to take over martin houses.
Here are some tips for maintaining the ideal hole size:
- Use durable hole casings – Metal or thick plastic casings resist enlarging or splintering.
- Avoid wood holes – Wood surrounds are more vulnerable to damage. Inspect wood holes frequently and patch any issues.
- Install entrance hole plates – Plates with correctly sized holes can be added to maintain hole dimensions.
- Routinely check holes – Inspect holes at the beginning and end of each nesting season and replace if enlarged.
- Educate others – Inform others helping with the house not to enlarge holes.
Conclusion
Installing and maintaining proper entrance hole size is one of the most important things you can do to attract purple martins. Follow the recommended hole diameter of 2 1/8 to 2 3/8 inches. This provides an open invitation for purple martins to nest in your house, while deterring problematic species.
With appropriately sized and well-constructed housing, you can look forward to those dazzling purple martins returning year after year.
