I heard some soft begging calls, and when I looked up to locate the source, I saw this Cliff Swallow (Petrochelidon pyrrhonota) landing at a nest.
In the picture above, note the orange or rust-colored rump. Below, look for the pale forehead and the dark, cinnamon- or chestnut-colored throat and side of the face.
When the adult left the nest, the reason for its visit was clear:
There were at least two young swallows visible near the opening to the nest. The adult was likely bringing food to those large, gaping mouths.
The nestlings withdrew, but then I noticed movement to the right:
An older nestling was visible in a second nest adjacent to the first one.