from The Century Dictionary.
- noun One who perches on or hangs over the rail or fence at a race-course, or a fair, not having a reserved seat.
- noun The Carolina rail or sora, Porzana carolina.
Sorry, no etymologies found.
He spent his mornings and afternoons either in his stables or at the extensive training-quarters of his stud, where he was as indefatigable a rail-bird as any pristine stable-boy.