I just bumbled into this: In 1978 Isaac Asimov judged a limerick contest run by Mohegan Community College in Norwich, Conn. He chose this as the best of 12,000 entries:

The bustard’s an exquisite fowl,
With minimal reason to growl:
He escapes what would be
Illegitimacy
By grace of a fortunate vowel.

It was written by retired Yale official George D. Vaill. Asimov said, “The idea is very clever and made me laugh, and the one-word fourth line is delightful.”