The Barn Swallow’s nesting and habitat preferences have made it the most abundant and widely distributed swallow species in the world. The species adapted to using human structures as nest-bases from their previous preference of nesting in caves (although a single population on California’s Channel Islands still chooses to nest in its ancestral cave-grounds), and today you can find Barn Swallows nesting nearly anywhere in the US, even ranging as far afield as southern Alaska.
Since they nest on man-made structures so often (hence their common name, as well as their species name rustica in the genus Hirundo), they make for a great focal species for Celebrate Urban Birds given that their habitat of choice can coincide with rural, suburban, and urban landscapes that include buildings, open areas, and water, especially bodies of which provide a source of mud. As you can see in the photos above and below, mud is the main building material for their nests, as it is for Cliff Swallows, a few of which are featured in these slideshows! Barn Swallows are also frequent subjects of the Funky Nests in Funky Places challenge at Celebrate Urban Birds.
In the slideshow above, you can see Barn Swallows gathering mud from the shore of some body of water (it can be anything from a river to a lake, although preferably there is grass or straw near or mixed into the mud so that the birds can more easily create the pellets that will be the building blocks for their nest). Both parents build the nest after having explored several potential nesting sites; once they’ve chosen one, they start construction by creating a small shelf that they can sit on and add the sides of the nest to. The pair can either build a semicircular cup plastered to a wall, or a full cup perched on top of a horizontal surface like a roof beam or other objects, as you can see in these slideshows.
When the main body of the nest is complete, the interior of the cup is lined with grass and feathers, and as in other swallow species (especially Tree Swallows) colonial groups might experience severe nest-lining theft — in these areas, if you take a handful of feathers and throw them in the air or leave them outside, you might see swallows swooping in to engage in a free-for-all to retrieve the precious bed-lining. Sometimes Barn Swallows reuse old nests, as long as they seem clean and free enough of parasites, and when they do so they throw out any old feathers and replace them. They also add new mud to the rim of the nest, which might explain some of the striation of mud colors in many of these photos.
So if you find a nest stuck to your walls or rafters and you see that there’s a pretty significant amount of mud in it, chances are it’s a Barn Swallow’s nest! If instead of mud there seems to be a bunch of greenish moss in the construction, it is more likely a phoebe’s nest. Barn Swallows generally lay 3-7 eggs per brood, and their eggs are a pinkish/creamy white, spotted with brown or gray.
To learn more about how to differentiate Barn Swallows from similar species, click here!