jets/rubies might be the best solution several reasons:
(1) no relation to gender roles,
(2) sound like gents and ladies, satisfying those who cognitively have difficulty
associating larks and robins with the corresponding roles.
(3) easier and faster to say. Jets, unlike larks, has no hard consonant. Rubies has a
hard consonant "b", but the sound of the "u" leaves one's lips and
tongue positioned perfectly to utter the "b". (This is a benefit to new
callers, who often have difficulty prompting on time.)
-----