The Purple Martin ( _Progne subis_ ) is the largest swallow species in North America, known for its distinctive dark plumage and reliance on human-provided housing across the eastern part of the continent. Their nutrition is derived exclusively from insects captured in flight, making them obligate aerial insectivores. This highly specialized diet means Purple Martins consume no seeds, berries, or ground-dwelling prey.
The Core Diet of Aerial Insects
Purple Martins capture flying insects opportunistically while airborne. Their menu changes daily based on insect swarms and atmospheric conditions. They primarily consume relatively large, soft-bodied insects, which they catch and swallow quickly in flight.
Primary food items include wasps, winged ants, beetles, moths, and true flies like house flies and crane flies. Dragonflies are a particularly important prey item during the breeding season, providing substantial protein for adults and nestlings. The belief that Purple Martins significantly control mosquito populations is inaccurate, as mosquitoes are typically active at twilight or near the ground, where the martins rarely forage.
Hunting and Foraging Behavior
Purple Martins acquire all their food through hawking, a technique involving agile pursuit and capture of prey while flying. They are exceptionally swift and maneuverable, often foraging at high altitudes to take advantage of insect migration patterns. Adults commonly hunt between 150 and 500 feet, though they pursue insects over 1,000 feet on warm mornings.
Foraging altitude is directly influenced by weather; on cool or cloudy days, the birds fly low, sometimes just above the ground or water, where insects congregate. This aerial lifestyle also extends to hydration, as Purple Martins drink by skimming the surface of lakes or ponds and scooping up water with their lower beak while in continuous flight. Captured insects are often compressed into a tight ball before being consumed or delivered to the young.
Specialized Nutritional Needs for Nestlings
The breeding season places immense caloric and mineral demands on adult martins, who must feed themselves and a brood of four to six nestlings. Parents continually hunt, bringing back a high volume of insects to support the rapid growth of their young. The insects are delivered to the nestlings as a compacted food bolus, sometimes containing hundreds of individual prey items.
Beyond protein and fat, breeding female martins and nestlings require significant calcium intake for eggshell formation and skeletal development. Since insects often lack sufficient calcium, martins seek out extraneous sources, such as crushed snail shells or ground eggshells. Landlords often provide baked and crushed chicken eggshells as a readily available supplement, which the martins consume and feed to their young.
Supplemental Feeding by Humans
Purple Martins cannot be sustained by conventional seed feeders, but supplemental feeding can be lifesaving during periods of inclement weather. Extended cold snaps or heavy rain drastically reduce the availability of flying insects, putting the birds at risk of starvation within a few days. Supplemental feeding is a short-term intervention used to bridge these gaps until natural prey returns.
Supplemental foods must mimic the natural diet, including freeze-dried or live crickets, mealworms, or finely chopped scrambled eggs. The delivery method is as important as the food itself, as martins are programmed to catch food in the air. Landlords often use the “tossing” method, flinging crickets or small pieces of egg into the air to encourage the birds to catch them in flight. Platform feeders, placed near the colony, can also be used alongside tossing to train the birds to recognize the artificial food source.