The Purple Martin (Progne subis) is the largest swallow species in North America. This migratory, cavity-nesting bird relies on human-provided housing, such as specialized gourds and multi-compartment birdhouses, particularly in the eastern population. Martins often form nesting colonies, creating a unique relationship with the people who manage their homes. Understanding their nesting cycle, including the characteristics of their eggs, is important for colony managers.
The Distinct Color and Appearance
The most direct answer to the question of color is that Purple Martin eggs are a uniform, pure white. They are notably smooth and non-glossy, lacking any of the spots, speckles, or markings common on the eggs of many other bird species. This absence of camouflage is typical for birds that nest within dark, enclosed cavities where visual concealment from predators is not required.
The eggs are slightly oval in shape and are laid directly into the cup of the nest material. The plain white coloration is a definitive characteristic that helps distinguish them from other eggs that might appear in a martin house.
Clutch Size and Nesting Behavior
The female Purple Martin typically deposits between three and eight eggs, with a common range being four to six eggs per clutch. She lays one egg each day until the clutch is complete. Incubation generally commences once the second-to-last egg has been laid.
This incubation period lasts approximately 15 to 18 days before the young hatch. The nest is a somewhat crude structure built inside the cavity, composed primarily of grass, twigs, and mud. Martins often line the interior nest cup with fresh, green leaves, a behavior thought to aid in sanitation or temperature regulation.
Distinguishing Purple Martin Eggs from Invaders
Identifying the pure white Purple Martin egg is important for colony managers, as it helps distinguish them from eggs belonging to invasive competitor species. The unmarked nature of the martin egg provides a clear contrast to those of common cavity invaders. For example, the non-native European Starling often lays eggs that are a pale, uniform powder blue.
The House Sparrow, another aggressive competitor, produces eggs that are smaller and noticeably speckled. These eggs typically exhibit a sandy-brown base color covered with dark brown spots or blotches. Finding any egg that is blue, brown, or marked with speckles within a martin compartment indicates it belongs to a different species.