Purple Martins are the largest swallows in North America, and their nesting habits are unique among common cavity-nesting birds. The appearance of their nest is inseparable from the structure they choose to build it in. In the eastern half of the continent, this structure is almost entirely dependent on human-provided housing, such as birdhouses and gourds. The actual nest is a specific, bulky collection of materials found within the compartment’s confines, rather than the external box.
Preferred Nesting Cavity and Location
A Purple Martin nest is always built inside a pre-existing cavity. In the eastern United States, the nest is nearly always found inside a multi-compartment birdhouse or a hollowed-out gourd hung from a pole in an open area. Western populations still rely more on natural sites like abandoned woodpecker holes or saguaro cacti cavities. The nest itself is a shallow, bulky cup constructed on the floor of the chosen compartment.
The nest material typically fills the entire floor area of the cavity, leaving a small, depressed bowl in the center to hold the eggs. Commercial housing compartments are usually a minimum of six by six inches. A key requirement for the location is an open flyway, meaning the structure is placed at least 40 to 60 feet away from tall trees or buildings that could obstruct the bird’s aerial approach. The nest is situated in a relatively dark, enclosed space, with only the entrance hole allowing light and access.
Construction Materials and Unique Features
The Purple Martin nest is coarse and somewhat messy. Both the male and female contribute to its creation, building a foundation of twigs, plant stems, and coarse grasses. This material forms a thick mat that can reach up to an inch in depth across the floor of the compartment.
A unique feature often present in the early-season nest is a mud dam, a rim or semicircular wall of mud and small sticks built directly behind the entrance hole. This dam restricts access, helping the martins defend their space against competitors like House Sparrows and European Starlings. The final lining of the nest cup consists of fresh, green leaves. These leaves, often stripped from trees like oak, cherry, or pear, are added throughout the incubation period. This addition of green foliage is thought to help control parasites within the nest.
Eggs and Young: What the Nest Contains
Once construction is complete, the shallow cup holds the clutch, which typically consists of four to six eggs, though the range can be from three to eight. Purple Martin eggs are pure white and completely unmarked, lacking the spots or speckles common in many other bird species. The female performs the majority of the incubation, which lasts approximately 15 to 18 days before the young hatch.
The hatchlings are altricial, born naked with closed eyes and a pinkish skin tone. As the young grow, the nest remains remarkably clean due to parental behavior. The nestlings expel their waste inside a tough, white membrane called a fecal sac. Adult martins carefully remove these sacs, either consuming them or flying them away from the nesting site. This removal of waste reduces scent that could attract predators and maintains a sanitary environment until the young fledge, about four weeks after hatching.