The Barn Swallow (Hirundo rustica) is the most widespread species of swallow in the world, with a natural distribution spanning over 251 million square kilometers globally. These birds are known for their distinctive blue upperparts, long, deeply forked tails, and their preference for open country with low vegetation, such as pasture, meadows, and farmland. They have adapted to living alongside humans, often nesting in barns and other man-made structures.
Identification of Barn Swallows
Barn Swallows are easily identified by their long, forked tails, which they use for stability during flight. They have blue backs, buffy breasts and bellies, and orange throats and foreheads. The female is similar in appearance to the male, but the tail streamers are shorter, the blue of the upperparts and breast band is less glossy, and the underparts paler. The juvenile is browner and has a paler rufous face and whiter underparts.
Dietary Habits: Primarily Insectivorous
Barn Swallows are primarily insectivores, with approximately 99.8% of their diet consisting of animal matter. They are aerial insectivores, meaning they hunt and eat insects while flying, often displaying stunning flight patterns in the process. These birds catch bugs while flying fast in the air, and eating many insects helps them stay energetic and strong.
Preferred Prey
Flies are a preferred food, including horse flies, crane flies, and robber flies. Stinkbugs, leafhoppers, and plant lice are also common prey. Less commonly eaten are ants, bees, parasitic wasps, predaceous ground beetles, ladybird beetles, weevils, dung beetles, and dragonflies. Caterpillars are rarely consumed due to the Barn Swallow's aerial foraging strategy.
Seasonal Variations
The Barn Swallow diet changes with the seasons. In spring and summer, insects are many and easy to find. During fall, they eat fewer bugs and sometimes catch spiders or small seeds.
Read also: The Dietary Habits of Barn Owls
Foraging Behavior
Barn Swallows typically feed by day in open areas 7-8 m (23-26 ft) above shallow water or the ground often following animals, humans, or farm machinery to catch disturbed insects; they may also pick prey items from the water surface, walls, and plants. Open areas such as pastures and plowed fields are preferred for foraging. Barn Swallows can often be observed dutifully foraging for pesky insects behind tractors as fields are plowed and planted.
Nutritional Value and Importance of a Varied Diet
Barn swallows eat mostly flying insects, which provide vital nutrients for their health. A varied diet helps keep their energy high and supports growth. They need a balanced diet for good health, including proteins from insects to grow strong and stay energetic and active.
Role in Pest Control
Barn Swallows may be able to significantly reduce crop pest insect populations. For example, a study conducted in Poland (Orlowski et al., 2014) analyzed Barn Swallow nestling faecal sacs and found that 17.8% of the nestling diet was oilseed rape pests, with an additional 5.3% being other arable crop pests.
Threats to Food Sources
Finding food can be hard for barn swallows. Weather changes can make insects scarce. Rainy days mean fewer bugs to catch. Pesticides on farms reduce insect numbers too. When bugs are less, swallows must fly farther to eat. This can make them tired and weak. Lack of food can affect their health and survival. Protecting their food sources is important.
Management and Conservation
Barn Swallows are one of the few bird species that have benefited from European settlement, but results from the North American Breeding Bird Survey indicate a 1.1% range-wide decline in North American populations from 1966-2012. Similarly, Barn Swallow populations have declined in Europe. The declines are largely attributed to increased pesticide usage, reduction of livestock grazing, reduction of on-farm ponds, and reduction of semi-natural habitats on farmlands (hedgerows, etc.). These changes have resulted in decreased invertebrate abundance and diversity, reducing food availability for adult and nestling swallows.
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Conservation Strategies
To support Barn Swallows, it's important to maintain open areas with plenty of insects nearby. Some growers will add narrow wooden ledges to walls or under eaves to provide nesting space. Nest removal at the end of the breeding season can help prevent buildup of ectoparasites. However, care must be taken in nest placement because Barn Swallows can be pests when they nest above food processing areas and drop feces.
Nesting Habits
As their name implies, Barn Swallows often nest in groups in rafter beams of barns in open cup mud nests. The neat cup-shaped nest is placed on a beam or against a suitable vertical projection. It is constructed by both sexes, with mud pellets collected in their beaks and lined with grasses, feathers, algae, or other soft materials. The female lays 2 to 7 reddish-spotted white eggs and incubates them for 14-19 days. Altricial (helpless) chicks fledge 18-23 days after hatching but stay with, and are fed by, the parents for about a week after leaving the nest.
Barn Swallows and Humans
Barn swallows are attractive birds that feed on flying insects and have therefore been tolerated by humans when they share their buildings for nesting. The Barn Swallow has adapted to human development, with more structures providing more nesting habitat.
Read also: Understanding Swallow Nutrition