Bank Swallow Nest Colony

     The Bank Swallow is a common and localized breeder in the state of Connecticut. With their darting flight, they are often seen over larger rivers, feeding frantically on flying insects. Unfortunately for many of us, this is typically the only way we ever get to enjoy these small, brownish birds.

     Early one morning, while birding in the Hartford North Meadows, I caught sight of a flock of Bank Swallows feeding over an inlet alongside the Connecticut River. As I sat and admired their incredible aerial pursuits, I noticed that most of the swallows were moving inland, rather than toward the river.

     Curious, I made it a point to follow their movements and see exactly where they were heading. My curiosity eventually led me to a sand and gravel pit adjacent to the meadows. After a few minutes of diligent searching and skirting dump trucks, I was thrilled to have discovered a colony of Bank Swallow high upon a large mound of dirt.  

     Bank Swallows, as their name implies, use vertical banks along rivers to dig nest burrows. If available, Bank Swallows will also make use of artificial sites such as sand quarries and road-cut banks. Both of these sites allow swallows to easily excavate burrows into eroding and loosened soils. 

Bank Swallow excavating burrow

     Recognizing that this was a unique opportunity, I decided to spend some extended time with the North Meadows colony. From the cover of my car, I was able get up close and personal with these birds.

     Interesting behaviors at the nest colony included a variety of physical interactions. Constant fighting over nest holes and mates often resulted in pairs fluttering toward the ground, pecking at each other. Vocal threats and pushes also ensued when intruders mistakenly entered wrong burrows.

     Another form of behavior I observed involved the excavation of a nest burrow. At two of the nest holes, dirt was briefly seen being forced out of the entrance tunnel by use of the swallow’s feet.  A more thorough explanation of this and other burrow-digging techniques is provided here from the pages of The Birds of North America Online.

   Bank Swallows have smaller, more conical bills, and a proportionately larger cucullaris-lateral rectus muscle complex than other swallows (Gaunt 1965). Burrows are dug with the bill, feet, and wings (Stoner 1936) as birds cling to a slight projection on the bank face, and dig using their bill in a rapid, slashing motion and feet in a scratching motion. Dislodged material from inside the burrow is ejected with vigorous kicks and wriggling body and wing shuffling movements. Burrows are excavated by groups of individuals, and excavation tends to be clustered in colony so that breeding is synchronized within sections (Hoogland and Sherman 1976, Freer 1977, Sieber 1980).

     Once a burrow is completed, the terminal end (chamber) is slightly enlarged upwards and to the sides. The nest chamber floor is constructed to be level with the burrow floor. Bank Swallow nest material includes plant stems, grasses, rootlets and leaves. Clutch size ranges from two to seven eggs.  

     As important as it is for Bank Swallows to find suitable nesting surfaces, it is equally important for the swallows to have prime foraging habitat surrounding the colony. Foraging occurs widely over most open lowland habitats such as agricultural areas, wetlands, grasslands and rivers.