The Tree Swallow (Tachycineta bicolor) is a small, iridescent songbird distributed widely across North America. It is classified as an obligate aerial insectivore, meaning its survival depends almost entirely on catching flying insects during the warmer months. This specialized diet and the bird’s unique ability to process certain foods allows it to arrive earlier and linger later than most other migratory swallows.
The Primary Menu: Airborne Invertebrates
The vast majority of the Tree Swallow’s nutrition comes from soft-bodied, flying invertebrates, often making up over 99 percent of its food intake during the breeding season. Flies, particularly midges, gnats, and other true flies (Diptera), commonly constitute the largest single portion, sometimes accounting for 40 percent of the adult diet. They also consume a wide variety of other insects, including beetles, ants, wasps, and moths.
The swallow’s diet is heavily influenced by proximity to water, as emerging aquatic insects are a high-value food source. Prey like mayflies, dragonflies, caddisflies, and stoneflies are frequently targeted, offering the rich supply of protein and fat necessary for raising young. Nestlings are fed these insects, which are constantly brought to the nest by both parents. A single nesting pair, including their brood, can consume an estimated 300,000 insects over the course of a 45-day nesting period.
Foraging Techniques and Hunting Behavior
Tree Swallows are masters of “aerial hawking,” a technique where prey is captured directly from the air while the bird is in flight. Their narrow, pointed wings and forked tails grant them the high-speed maneuverability required for this acrobatic hunting style. They typically forage over open areas, such as fields, marshes, or bodies of water, where insect populations are concentrated.
The birds must adjust their foraging height and speed based on environmental conditions, as insect activity is closely tied to temperature. When the weather is warm, they can hunt at higher altitudes, but during cold snaps or rainy periods, flying insects become scarce or remain near the ground. Under these conditions, the swallows must fly lower and faster to secure enough food to survive. They also drink water by dipping their lower bill into the surface of a pond or lake while skimming across it in continuous flight.
Coping with Scarcity: Non-Insect Food Sources
Tree Swallows possess a unique dietary flexibility that distinguishes them from most other North American swallow species. They have the ability to switch temporarily to a diet of plant matter when insects become unavailable. This mechanism is particularly important during periods of resource scarcity, such as unseasonal cold weather or during early spring and late fall migration.
The main non-insect food source is the fruit of the bayberry (Myrica) and wax myrtle plants. These berries are coated in a waxy substance that few other birds can digest, but the Tree Swallow’s digestive system can process the fat and energy contained within. While this plant matter is a survival food, it enables them to extend their residency in northern regions longer than other aerial insectivores.