Structural characters and call notes remain the most diagnostic traits.
One means of distinguishing the willow tit from the marsh tit is by call notes.
Where one species overlaps in territory with another having a similar call note, the frequency of the first species' song is adjusted upward by about 0.3 kilohertz.
A parent feeds only its own chick, recognizing the chick by its call note.
Black-chinned hummingbirds produce a variety of call notes, typically used while chasing other birds.