Puzzled

How in the world can "sad culvers" be taken to mean "erect [male] nipples"?

The thought of erect nipples as pigeons (their beaks perhaps?) is some image. Perhaps raising associations of pigeon's (or dove's) milk? Though bird milk is not milk, per se. Pigeon's milk is tied to a traditional April fool's joke. Is this a joke?

"Culvert" would make another kind of sense, being a drainage or other kind of ditch or tunnel (like the kind cows pass through under a road from one pasture to another--we call those culverts). But I suspect no mistake.

Calvers? As in that which calves. More bovines. 'Nother pasture.

Hugenormous dictionary & internet no help. Puzzling them pigeons. Move on.