Making Space for Barn Swallows

by Mara Silver, founder of SwallowConservation.org

Almost everyone is familiar with the Barn Swallow silhouette—the streamlined, aerodynamic birds with pointed wings and long, forked tail feathers. Although it may look like they are flying acrobats having fun, they are actually maneuvering in flight to catch insects, their sole food source. Barn Swallows aren’t necessarily faster than other swallows, but they do make faster, tighter turns using their forked tail for stability.

Barn Swallows are popular in culture and often appear in art, symbolizing good luck, a return home, and the return of spring. Another reason for their popularity may be that they nest in close association with people. Barn Swallows have a nearly worldwide distribution comprised of several subspecies, all of which are heavily dependent on human-made structures for nesting sites. It is thought that at one time they nested in caves and on rock faces, but ancient written accounts indicate that they have nested alongside humans for most of our history. In North America, they are commonly found on farms, where they nest inside barns and outbuildings, forage over open fields for insect prey, and collect plentiful mud for nest-building. They also nest under bridges and docks and on other human-made structures. They are often confused with Cliff Swallows, which also nest in close association with humans but, unlike Barn Swallows, construct bottle-shaped mud nests under the eaves of buildings, in culverts, and under bridges (in addition to cliffs).

When small-scale farming started to decline in North America, so did the Barn Swallows. The North American Breeding Bird Survey indicates a 35% decline between 1966 and 2019 (Sauer et al. 2020) and a 74% decline in Canada between 1970 and 2022 (Smith et al. 2024). Since the 1980s, the decline has become even steeper, with Barn Swallows notably disappearing from traditional nesting sites. While the reasons for decline are not known with certainty, several factors may be affecting aerial insectivores in general, such as habitat loss, changes in insect prey, pesticides, and climate change and associated extreme weather events. Barn Swallows haven’t received much conservation attention, perhaps because they still are perceived as a common bird. However, the current widespread declines across most of the continent indicate that conservation action is warranted. Many are surprised to learn that Barn Swallows were listed as Threatened in Canada in 2011, and although the status was changed to Special Concern in 2021, they are still listed as Threatened in Ontario and New Brunswick and as Endangered in Nova Scotia. Some claim that with the loss of human-made structures for nesting sites, populations are retracting to their “natural” level. However, interestingly, even though there are natural nesting sites still available, Barn Swallows consistently use human-made structures instead—and continue to disappear from these.

The positive news is that when conservation measures at the nesting habitat level are implemented, nesting colonies can rebound.

Experimenting With Attractants

One of my study sites is an 1880s barn that had an active Barn Swallow colony when the farm was in operation through the 1970s. The barn was closed up (denying the swallows access) from the early 1980s until 2012, at which point there was just a single pair nesting in an open horse barn. In 2012, I opened up the entire barn, both the hayloft and lower stanchions, so the swallows could gain access to the interior. I also created a mud source by digging a shallow depression, lining it with lake liner, and filling it with wet soil and natural clay, which I kept wet through the nesting season. Finally, I installed artificial nest cups of my own design in the barn. That same year, three pairs of Barn Swallows nested in the barn and were seen using the mud source. Over the next 12 years, using the same management techniques, colony size gradually increased, until in 2024 there were 15 pairs nesting at the site.

In 2014, I closed off the hayloft area because nests were appearing to become overheated; Barn Swallows generally place their nests very close to ceilings, which makes them vulnerable to heat conducted from roofs. Instead, I opened additional windows in the stanchion area to provide even more access to this area. This is where most of the pairs nest, though over time I have noted that as the colony has grown, swallows are nesting in novel areas, like under the barn in two separate locations. Barn Swallows nest in groups, but they are not highly colonial (Snapp 1976), and some seem to prefer to nest away from the crowd. Barn Swallows are also attracted to old nests (Safran 2006) and often return to the same colony to nest annually (Shields 1984), making it especially important to protect long-held nesting sites. For more details and photos of the process I undertook and the results, visit my website documenting this work.

Not everyone has the appropriate habitat for Barn Swallows, but if you or someone you know does, taking the steps outlined above just may make a difference!

Some Factors to Note:

• Barn Swallows seeking nesting sites will explore upward in a multilevel building, and if there isn’t an open window or door on the top level, they can become trapped because they don’t know to fly back down.
• You can give Barn Swallows a head start on their nests by making a DIY nest platform or by purchasing ready-made clay or wooden options.
• Barn Swallow nests are fairly easy to monitor; just remember not to approach nests after the young are 13 days old, or they may fledge prematurely.
• Monitoring your nests and submitting your data to NestWatch can help scientists better track Barn Swallow populations.

References

• Safran, R. J. 2004. Adaptive site selection rules and variation in group size of barn swallows: individual decisions predict population patterns. American Naturalist 164: 121–131.
• Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski, Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link. 2019. The North American Breeding Bird Survey, Results and Analysis 1966 – 2019. Version 2.07.2019 USGS Patuxent Wildlife Research Center, Laurel, MD. Available at https://www.usgs.gov/tools/north-american-breeding-bird-survey-results-and-analysis.
• Shields, W. M. 1984. Factors affecting nest and site fidelity in Adirondack barn swallows. Auk 101: 780–789.
• Smith, A. C., M.-A. R. Hudson, V. I. Aponte, W. B. English, and C. M. Francis. 2024. North American Breeding Bird Survey – Canadian Trends Website, Data-version 2023. Environment and Climate Change Canada, Gatineau, Quebec, K1A 0H3. Available at https://wildlife-species.canada.ca/breeding-bird-survey-results/.
• Snapp, B. D. 1976. Colonial breeding in the Barn Swallow (Hirundo rustica) and its adaptive significance. Condor 78: 471–480.