While birding with Alfredo Tol Gonzalez on Atitlán volcano, Guatemala on 8th January 2024, he pointed me to a Brown-backed Solitaire / Braunrückenklarino (Myadestes occidentalis) with an aberrant song at about 2250 m altitude. It sounded like a primitive, unfinished version of the regular, crystallized song of this species – particularly obvious in the second half of the strophe. Alfredo stated that this bird had been singing in this exact spot for several years and that no other birds around where singing this variation. A young bird’s plastic song or subsong can be excluded in this case and hampered song development seems to a likely explanation.
Bird with aberrant song (be patient, it’s a little hesitant in the beginning 😉
Bird with normal song for comparison
This incomplete song from a different location makes me think more of subsong