The barn swallow (Hirundo rustica) is one of the most widely distributed swallow species globally, easily recognizable by its deeply forked tail and shimmering blue-black plumage. This highly migratory bird travels vast distances between its northern breeding grounds and southern wintering areas. The barn swallow is classified as an obligate aerial insectivore, meaning its entire diet is composed of insects captured while flying. This specialized feeding habit dictates its behavior and habitat selection near open areas where flying arthropods are abundant.
Primary Prey: The Insect Menu
The diet is composed of small, soft-bodied arthropods captured on the wing. True flies (Diptera) often make up a significant portion of their intake, sometimes constituting up to 70% of the diet in breeding areas. These include house flies, horse flies, and mosquitoes, making the barn swallow a beneficial presence around human settlements and livestock.
Other important prey items include wasps and bees (Hymenoptera), which can account for over 20% of the diet, along with beetles (Coleoptera) and true bugs (Hemiptera). They often select for insects between 4 to 8 millimeters in body length. This preference for relatively larger insects helps maximize the energy gained from each capture.
A single barn swallow can eat over 1,000 insects per day during peak feeding times, such as when raising young. They occasionally consume other small invertebrates like spiders or snails, particularly when flying insects are scarce. The protein-rich diet provides the necessary fuel for their highly energetic and acrobatic lifestyle.
Aerial Foraging Techniques
Barn swallows hunt using aerial hawking, capturing prey directly from the air without landing. Their exceptional agility and deeply forked tail allow for the rapid, erratic maneuvers needed to pursue flying insects. They are capable of high-speed flight, sometimes reaching close to 75 kilometers per hour.
These birds forage in open habitats such as over fields, pastures, and water bodies, often flying low to the ground or just skimming the water’s surface. This low-altitude flight allows them to exploit the wind shear layers near the earth, which provides an energy advantage for sustained flight. They rely on visual cues to spot their prey, which are then quickly intercepted with their wide, gaping mouths.
Foraging behavior is influenced by weather conditions. Before a rainstorm, when atmospheric pressure drops, insects tend to fly lower to the ground, which is why barn swallows are often seen swooping low over fields. If poor weather persists, making aerial hunting difficult, the swallows may temporarily switch to picking dead or sluggish insects off of plants or surfaces.
Hydration and Supplementation Needs
While the barn swallow’s food provides some moisture, the birds must actively seek out water sources to remain hydrated. They drink by performing water skimming, flying rapidly and low over the surface of a pond, lake, or stream. During this maneuver, they dip their lower beak into the water, scooping up a mouthful without breaking their flight.
Barn swallows also require certain supplements for digestive and physiological health. They occasionally ingest small pieces of grit or tiny pebbles to help their gizzard grind the tough exoskeletons of hard-shelled insects they consume. Additionally, they seek out sources of calcium, such as crushed oyster shells or eggshells, particularly during the breeding season to support egg production and the development of their young.