Unspotted Saw-whet Owl was once thought to be very rare in highlands of southern Mexico and Central America. Recent studies on the distribution of this owl by Knut Eisermann and Claudia Avendaño have shown that in Guatemala it is widespread throughout the highlands.
Eisermann, K. & C. Avendaño (2017) The owls of Guatemala. 447-515 in P. L. Enríquez (ed.) Neotropical owls: diversity and conservation. Springer, Cham, Switzerland.
Eisermann, K. & C. Avendaño (2018) An update on the inventory, distribution and residency status of bird species in Guatemala. Bulletin British Ornithologists' Club 138: 148-229.
Knut Eisermann described several vocalizations of Unspotted Saw-whet Owl, including territorial toot calls, contact calls, and begging calls. Toot calls can be surprisingly similar to vocalizations of Guatemalan Pygmy-Owl (Glaucidium cobanense). Differences are discussed in a paper in Neotropical Birding