Swallows, including the Barn and Tree Swallow, are known for their graceful, acrobatic flight. As aerial insectivores, their entire life cycle, especially the rapid growth of their young, is dependent on catching flying insects. The energy required to sustain a nestling’s development demands a specialized, protein-rich diet delivered constantly by the parent birds. This unique feeding strategy ensures the baby swallows grow quickly enough to fledge and begin the demanding task of catching their own food in the air.
The Natural Diet of Nestling Swallows
The diet of baby swallows is composed entirely of insects caught in flight. Their digestive systems are adapted to process this high-protein prey, which provides the necessary fuel for their rapid growth rate. Parent swallows do not feed their young a single insect at a time; rather, they collect numerous small prey items into a soft mass called a bolus. This bolus is then delivered whole to the nestling.
A single bolus can contain anywhere from 19 to 34 insects, and a brood may consume an estimated 8,000 prey items per day. The prey composition is diverse, including soft-bodied insects like flies, midges, and gnats. Aquatic insects such as mayflies and damselflies, which contain beneficial omega-3 fatty acids, are particularly important and can make up a significant portion of the diet. The high nutritional density of these insects is essential for the rapid tissue and feather development required for a young swallow to fledge successfully.
The Continuous Feeding Cycle
Swallow nestlings possess high metabolic rates, necessitating a continuous supply of food. Parents must hunt almost non-stop from dawn until dusk during the nestling period to keep up with the demand. The rate at which adults return to the nest with food increases as the young birds grow, often reaching a peak around day eight after hatching.
This constant provisioning is necessary because nestlings may gain weight rapidly, sometimes reaching fifteen times their hatching weight by the time they are twelve days old. The parents’ feeding efforts are guided by the nestlings’ begging behavior, which includes raising their heads and opening their brightly colored mouths. Environmental factors like cold or wet weather can reduce the availability of flying insects, forcing the parents to work harder and sometimes leading to slower growth rates.
Common Feeding Mistakes to Avoid
Never attempt to feed an orphaned baby swallow common household items. Foods like bread, seeds, milk, or household scraps are highly detrimental to a baby swallow’s health. Bread offers virtually no nutritional value for a developing bird, leading to severe malnutrition despite filling the stomach.
Milk is dangerous because birds are not mammals and lack the necessary enzymes to digest lactose, causing severe digestive issues. Furthermore, attempting to give a nestling liquid, such as water via a dropper, carries a high risk of aspiration, where the fluid enters the windpipe. This can quickly lead to fatal pneumonia or drowning. For an orphaned swallow, the only correct course of action is to contact a licensed wildlife rehabilitator immediately, as they possess the specialized insect-based diets and feeding techniques required for survival.