The Barn Swallow migrates by day, eats on the fly, and is found worldwide
Published: March 1, 2006
|The Barn Swallow, one of the world's best-known birds, offers remarkable lessons about migration. It's a single species distributed worldwide, but its behaviors vary considerably depending on where it nests. |
Most Barn Swallows travel long distances each year, but others make short jaunts between wintering and breeding areas. Unlike night-migrating songbirds, Barn Swallows fly mostly during the day. And they don't carry fat loads like other migrants; instead, they maintain energy levels by feeding throughout their journeys.
Biologists have identified up to eight subspecies of Barn Swallow (Hirundo rustica), all but one of which occur in the Eastern Hemisphere. The western subspecies (H. r. erythrogaster) breeds across North America, from southeast Alaska and Canada to northern Florida and central Mexico. It winters primarily in central South America, but vagrants occur north to Mexico and south to Tierra del Fuego.
Spring comes early for some Barn Swallows; birds have arrived in southern California in late January. Most migrants, though, return to southern states in early March and northern states and Canada in April and May. Fall migration begins around the second week of July and continues through October. Stragglers have been recorded as late as early December.
The most widespread Eurasian subspecies (H. r. rustica) breeds across Europe and into central Russia and northern Africa. It winters south of the Sahara Desert and in India. Banding data published in 1970 indicated that birds from western and central Europe winter in central Africa and birds from northern and eastern Europe winter in eastern Africa.
Spring and fall migrations follow a schedule similar to that of the American subspecies; peak passages occur by mid-March and in September. On both sides of the Atlantic, Barn Swallow migration typically precedes the flights of many other birds.
Welcome to Australia
Two to four subspecies breed in East Asia, including Russia, China, Korea, and Japan. They winter from India to Indonesia, and the race H. r. gutturalis recently expanded its winter range to northern Australia.
Two partially migratory subspecies in the Middle East add an unusual twist to the story of Barn Swallow movements. H. r. transitiva breeds in Syria, Lebanon, Jordan, and Israel; it appears to migrate no farther than northern Egypt. H. r. savignii stays even closer to home. After nesting in towns and villages along Egypt's northern Nile River, it disperses to nearby lakes and wetlands.
American and Eurasian Barn Swallows migrate in both short hops and longer, nonstop movements. Fall migrants in Great Britain have meandered along at 1-16 miles per day, but records show one bird flew as far as 121 miles per day. A juvenile banded in New York and recovered off the eastern coast of Panama averaged 56 miles per day in 44 days for a total of more than 2,400 miles.
The species migrates by day and forages as it moves. Cold and rainy weather and a lack of food can hold up migrating swallows for days, especially in spring.
Barn Swallows often follow lakeshores and coastlines, but they also migrate over open water. Some fly more than 600 miles over the Gulf of Mexico or the Mediterranean Sea, similar to the migrations of other songbirds. Nonstop flights are possible because the birds add fat before and during migration. Unlike some warblers and shorebirds that nearly double their weight prior to long-distance journeys, swallows increase their weight by about a third. European Barn Swallows, for example, weigh 18-19 grams in July and 24-25 grams in late August and September.
In addition to feeding during migration, swallows may need less fat than other birds because they opportunistically use thermals - rising bodies of warm air not available to night migrants. Unlike strict soaring behavior with little flapping, swallows intersperse lots of flapping flight with short glides. When the weather isn't favorable for soaring, the birds use powered flight, which burns more fat.
The long-distance champions among Barn Swallows are the European birds. Not only must they cross the Mediterranean from Italy or Spain, but they also must conquer the Sahara Desert. Recent research by European scientists shed light on how swallows cross up to 680 miles of sea and 1,850 miles of desert. Before departing from fall stopover sites, the birds add enough fat to cross both ecological barriers and do not appear to refuel substantially in North Africa. Birds in Italy that have more sea to cross deposit more fat than birds in Spain. This is undoubtedly an adaptation to the longer, nonstop trip.
Barn Swallow is not the only migrant that inhabits both sides of the globe. Parallel migrations also occur in Peregrine Falcon, Rough-legged Hawk, Purple Sandpiper, and Bank Swallow (known as Sand Martin in the Eastern Hemisphere). The migrations of the few worldwide bird species strongly suggest that populations separated by thousands of miles evolved similar migratory patterns because they face similar natural-selection pressures.