Bridges and Swallows

Cliff Swallows (Petrochelidon pyrrhonota)
building nests under a highway bridge.  Davie County, NC.

Bridges can be engineering marvels and architectural masterpieces.  Think Tower Bridge, Pont Neuf, Golden Gate Bridge and Brooklyn Bridge.  But even humble bridges can host treasures.  On a highway bridge over a small river near our home there is a nesting colony of Cliff Swallows.  Over 100 of these fast-flying aerialists are raising the next generation under this bridge.  Like bridges, the nests of Cliff Swallows are architectural wonders.

Video of Cliff Swallows collecting mud

to use in nest building.  Davie County, NC.

                        

Completed Cliff Swallow nest.  Davie County, NC. 

Cliff Swallows (Petrochelidon pyrrhonota) are small birds that are white below, with an iridescent blue back, an orange rump, reddish-brown face and a blue cap.  Just above the beak, in the center of their foreheads, they have an off-white spot, rather like the headlight of a motorcycle.  Cliff Swallows make their living by catching insects on the wing, giving their chattering call all the while.  They are neotropical migrants, returning each spring from their winter in South America.  Unlike most small birds that migrate at night, swallows migrate during the daytime and feed en route.   

 

Cliff Swallow engaged in nest building. This adult bird shows the spot
on its forehead  Davie County, NC.

 Cliff Swallows making nests.  Davie County, NC.

Originally, Cliff Swallows nested  (of course) on cliffs and were infrequent summer residents in the Southeastern United States.  But human structures, particularly bridges, have allowed them to expand their range.  During our time in North Carolina, we watched Cliff Swallows go from being a rare bird to become common breeding birds.  

 

Juvenile Cliff Swallow looking out of a nest.  Juveniles
lack the off-white spot on the forehead and have a striped throat.
Davie County, NC.

Cliff Swallow nests are marvelous works of design and construction. Their material of choice is mud,
collected from stream banks or puddles. The nest starts as a glob of mud attached to the cliff (or bridge) and grows one mouthful at time. Then the nest tapers to a spout, making a flask with the entrance pointing down. The swallows lay 3-4 eggs in their new nest and the eggs hatch in about two weeks. Juvenile Cliff Swallows look similar to the adults but with streaks on the throat and they lack the white forehead spot. The nestlings stay in their mud home for another couple of weeks then venture out on their maiden flight.

Adult Cliff Swallow feeding young in the nest.  Davie County, NC

 

A group of Cliff Swallow nests.  A juvenile looks out the nest
on the right while and adult flies in to feed young in another nest.
Davie County, NC.

Cliff Swallows may raise a second brood and stay around the nest colony for the summer.  In September, Cliff Swallows join other birds on their flights to their winter territories in the tropics.  Most migrate through Mexico and Central America headed for to their destination in Northern South America.   We are now in high summer and Cliff Swallow nests are active.  There may be a bridge near you with a nesting colony of Cliff Swallows.  Visit them and you can appreciate the fine construction of the nests and frenetic activity of the birds. 

Cliff Swallows resting and preening on a wire.  Davie County, NC.