Barn Swallows

Originally published in the Spring 2003 issue of the Iowa Barn Foundation Magazine.
Written by James J. Dinsmore, retired professor Iowa State University, and noted ornithologist.

It was 25 years ago, when a graduate student and I stopped at a farmstead near Hubbard, Iowa because I had heard that black-crowned night-herons, a rare nesting species in Iowa, were nesting in a farm grove.

We saw only a single night-heron, but I did get a vivid glimpse of how closely barn swallows are tied to farms, in general, and to barns, in particular, in Iowa. The owner of the farm, an elderly gentleman, told us how much he loved the birds and that he put out bird houses to attract them to his farmstead. He spent much of his time standing in or near the doorway to his barn. The barn was old and somewhat of a "leaner," but what I remember most was that barn swallows were constantly entering and leaving the barn while the farmer stood there.

It was clear that the barn swallows were welcome in his barn, as their flights took them within inches of his body as they whizzed through the doorway. The farmer seemed oblivious to the birds, but it was clear that he really enjoyed having them nearby. There must have been at least 8 or 10 swallows moving in or out of the barn, clearly engaged in picking out nesting sites within the barn. The union of humans and barn swallows was close that day.

I drove by this same farmstead a few weeks ago. I have traveled a nearby highway frequently over the years so I knew that the woodlot was still intact but hadn't noticed the barn. The farmstead appeared occupied--the occupant busy harvesting his crops-- but the barn was gone. The space where the barn had once stood was still somewhat open indicating it had probably collapsed or been torn down not too many years ago. I assume that the gentleman who loved the swallows had passed on and wondered if the new occupant has the same love for the birds as the previous owner. I also wondered, where were the barn swallows nesting?

That day still serves as a reminder to me of the remarkable tie that exists between humans and barn swallows. The tie is especially close during the nesting season when barn swallows build their familiar mud nest. I don't recall ever seeing a barn swallow's nest that was built in something other than a human-altered situation. For years, the most common nest sites have been in or on barns or other farm buildings. Barn swallows also commonly build their nests on the sides of bridges or similar structures. Although we usually think of barn swallows as being birds of rural areas, they will also nest in urban areas where they may plaster their nests to the side of a house. Areas around doorways or above light fixtures are favored nest sites and may lead to extended battles between the swallows and the homeowners. Not uncommonly, the human will "win" by knocking the nest down and driving the swallow away.

It is interesting to speculate how North American barn swallows lived prior to the arrival of humans, especially Europeans, on this continent. Presumably they nested in caves or on cliffs, but they probably were much less abundant then than they are now. Undoubtedly, the barn swallow is a bird species that has benefited greatly from the advances of civilization.

We North Americans often think of barn swallows as "our birds" without realizing that the species actually has an extensive range and spends much of the year outside North America. During the non-breeding season, barn swallows migrate to Central and South America where they spend the winter. In addition, barn swallows are a common nesting bird over much of Europe and temperate regions of Asia.

Several years ago, the morning after arriving in Japan, I was trying to clear jet-lag grogginess when I heard the twittering of birds outside my room. The calls sounded vaguely familiar, but I was certain that I would be seeing a new exciting species. Thus, I was somewhat disappointed when I opened the curtains and saw a barn swallow trying to build a nest on the outer wall of the building.

I had a similar experience in Alaska a few years ago. We spent several days in Nome, an isolated town on the Bering Sea in far western Alaska. There we saw a number of rare birds including several that were most likely to be found in Siberia, just over the horizon from us. Yet, among the birds, in a Native American settlement, there was a barn swallow. This bird was far north of its usual range and by its plumage, it was clear that this particular barn swallow was part of the Asian population. Thus, it had wandered across the Bering Strait to Alaska.

Barn swallows arrive in Iowa in early to mid-April after a long migration from their wintering grounds in southern Mexico, Central, and South America. They quickly bond into pairs and begin building their nests. They gather small globs of mud, fly to the nest site, and plaster the mud to a vertical surface. They generally start by building a narrow horizontal shelf of mud along what will eventually be the bottom of the nest. The barn swallows use that as a perch while building the rest of the nest and later finish the nest off by lining it first with dead grass, then feathers. Hundreds of trips are required to build the nest, which gradually takes shape as a fairly deep, cup-shaped structure open at the top. During their nest building season, it is common to see several barn swallows gathered at the edge of a small stream or puddle where they gather mud. They like to build nests on structures that have overhangs giving protection from rains that could wash the nest away.

Male and female swallows participate in building the nest, which takes from six to 15 days to construct. They may reuse an old nest by adding new mud to the structure. One nest was reportedly used for 17 years although not by the same birds for that entire time. After the nest is complete, the female lays eggs, one per day, until the clutch is complete. She may lay from 3 to 7 eggs, which are creamy white with small dark spots. In Iowa, barn swallows generally produce two clutches, with the first averaging 5 eggs and the second about 4 eggs. The eggs are incubated by both sexes and hatch in about 13 to 15 days. The young remain in the nest for about another 20 days. The adults feed the young a diet made up almost entirely of flying insects. When the young are about 12 days old, they begin a rather unusual practice, backing up to the edge of the nest and defecating over the side. These droppings may end up on the ground under the nest or as a layer along the rim of nest, sometimes causing barn swallows to be labeled "messy".

Barn swallows are the most common swallow found in Iowa and are one of the most abundant species in the state. Although we don't have an estimate of their population, in a study of nesting birds in Iowa completed in 1990, barn swallows were found nesting in every county and were the sixth most widespread nesting bird reported in the state. Part of that apparent abundance is because of the ease with which their nests can be found and monitored. Also the fact that barn swallows are so often found closely associated with humans makes them a conspicuous part of the bird life in Iowa. After the nesting season, barn swallows form flocks that may number in the hundreds or sometimes even low thousands. They often congregate near a lake, pond, or stream where large numbers of small insects may be found. It is not unusual to see dozens or more barn swallows lined up on a power line as they rest between foraging flights. Typically the birds are lined up evenly with just a little space between each pair of birds. Usually this distance is just enough to keep adjacent birds from being able to reach over and peck their neighbors. If two birds are too close to each other, there is generally a little posturing and one or both birds will shuffle along the wire until just the right spacing is achieved.

Although barns swallows can sometimes be messy, their zippy flights add zest to summer days. And the frantic pace they follow to raise two broods of young during the brief few months they spend with us is a familiar part of summer. Enjoy them while they are here and remember how they depend upon us for a place to live.