The bridge near Regenstein Hall on Northwestern’s south campus is the site of an amazing aerial display during late spring and early summer. No, it is not the Blue Angels. Performers are three species of nesting swallows.
Swallows are in the order of passerines, or perching birds, though they are most often seen on the wing, skimming insects off the water or out of the air with graceful precision. These three species are named for their nesting locations – cliff, barn and bank. All have the same basic shape, with long, pointed wings designed for fast flying. All are migrants, coming north only to breed. The cliff and bank swallows travel the farthest, arriving in spring from their wintering grounds in southern South America. All nest in colonies. All search for nesting areas protected from the weather.
Bank swallows (Riparia riparia) are small sand-
colored birds with white bellies and brown necklaces. They carve tunnels in vertical sand or dirt cliffs always near water. According to “Stokes Field Guide to Birds,” “Tunnels may be 20-40 inches long, slope upward, and end in a wide chamber where the nest is placed.” Their holes are easily detected in the sandbank just south of the bridge.
Barn swallows (Hirundo rustica) are mud-nest swallows with dark backs, orange bellies and deeply forked tails. They nest out of sight under the bridge, the only evidence being their incessant flight as they pick off insects over the water. The young have light orange bellies.
Cliff swallows (Hirundo fulva) are the stars of the show. Of the three, only cliff swallows are restricted to the Western hemisphere. Our human infrastructure, such as architectural overhangs, bridges and culverts, mimics the natural rocky walls and canyons of the original cliff swallow breeding grounds in the Western United States. Accordingly, cliff swallows have expanded their breeding range eastward. (Barn swallows also opt for human structures, as their name implies.)
Cliff swallows have rounded tails, white bellies, buff-colored rumps, chestnut throats, and black heads with a distinctive white “headlamp” on the forehead. They perch at their nests in full view. They are a quarrelsome bunch and can often be seen attacking one another on the wing or with their beaks.
The classic cliff swallow nest resembles a squat jug tipped on its side, with a tubular entrance hole. When the birds find an appropriate nest site, often previously used, and a supply of mud, they flock to the ground, flutter their wings vertically, stab their beaks into the mud until they are well-coated, and then fly to the nest spot. They fashion the mud into a ball and plaster it onto a wall, pellet by pellet. Construction may involve up to 1,400 trips. Nests are
often superimposed and require continuous repair.
Both male and female build the nest and do all the parenting chores. The eggs, usually three to six, are whitish with dark spots. It takes about five weeks from first egg to fledgling. After leaving the nest, fledglings gather in large groups. Parents locate their own young by the distinctive calls of their chicks.
Major nest hazards are humans, English sparrows, parasites and weather. Humans remove occupied nests when the colonies are inconveniently placed over heavily trafficked areas, even though the birds are federally protected by the Migratory Bird Treaty Act of 1918. Research concerning cliff swallows ranges from how to protect a colony for maximum productivity to how to place barriers to prevent nesting.
Sparrows definitely take their toll. In the Wilson Bulletin, September, 1942, Ervin O. Buss reports about a “managed” colony which grew to as many as 4,000 nests in Deerfield, Wis. When the first pair arrived in 1904, a young Mr. Bedeman, age 16, watched them and noticed that English sparrows “killed the young at an early age and dragged them from their nest. Mr. Bodeman declared war on them immediately. Shot was expensive and not easy to get in 1904, so selected gravel was substituted in his father’s muzzle-loading shotgun. … The weathered boards around the barn are densely pock-marked, attesting to thousands of rounds fired.” (Non-native English sparrows are not legally protected.)
The costs and benefits of colonial nesting are poorly understood and intensely researched. Colonies benefit in lean times, when a member of the colony finds a source of food and others follow. Male and female philandering is common. Females lay eggs in other’s nests and carry their own eggs in their beaks to drop off at a neighbor’s. Colonialism allows parasites, especially the swallow bug, to crawl from nest to nest. Nest sites are often abandoned after a few years, possibly due to the bug’s infestation; it can over-winter in unused nests for up to three years without a bite of food.
The vicissitudes of weather on nesting cliff swallows were demonstrated this year at Regenstein. The swallows, which typically arrive around May 1, arrived about May 23. Possibly the cold spring curbed insects, their major food source. Their arrival coincided with a dry spell when there was no mud. They turned to the beach. Their frenetic transport of sand daubs was doomed as the sand balls dried and dribbled to the ground. The birds left. Then the rains came, and the mud, and the swallows returned. In mid-June there were approximately 40 nests under the eaves, some occupied by sparrows, some complete, some on the half-shell. (see photo)
Cliff swallows usually have just one clutch a year.
We wish them well.
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