¿Qué ave utiliza barro para construir su nido?

La historia detrás de la respuesta

Swallow is correct. Barn and cliff swallows are famous “mud masons,” carrying beakfuls of wet mud mixed with saliva (and bits of grass) to build sturdy cup- or gourd-shaped nests on cliffs, bridges, and under building eaves. These colonial builders add hundreds of pellets, creating a hard, protective shell