NEST DETAIL. In my ocular estimate, the nest is about 0.35 - 0.40 m in height and 0.20 - 0.25 m in width. The entrance hole is roughly 50 - 75 mm in diameter.
To my eyes, the nest appears to be made of mud. It must have taken the smallish birds (Guaiaberos are about 165 mm in total length) quite some time to build a nest of such size and mass.
From a human civil engineer to a fellow builder (of the avian kind), I give my respect and salute this achievement. I had to go through years of college education, and thereafter some more in apprenticeship,
to learn to build things. These wonders of nature are pre-wired since birth, or "egghood," to do it automatically.

[350D + Sigmonster, MLU]