In his notes, the yellow-belly may be said to take after both the least flycatcher and the wood pewee.
Around the middle of each corn fairy is a yellow-belly belt.
Praed was a quitter—a yellow-belly—besides being—But he stopped there.
A coward; a poltroon: He is a contemptible yellow-belly, scared of his own shadow
[1930+; probably a rhyming expansion of yellow; influenced by the early 1800s sense, ''a Mexican, esp a Mexican soldier,'' perhaps fr the color of their uniforms]