older kid's or YA fantasy series where characters turn into birds of prey

[Ms Atoz]

I'm a librarian with a patron trying to track down a fantasy series she read and loved as a child in the late '60s/early '70s. She thinks the books were written by a British author, were published in the '50s or '60s, and involved the characters turning into birds of prey (a merlin, a falcon, etc).

She's quite sure that she's not thinking of any of the following:
The Sword in the Stone (and its sequels) by T. H. White
The Earthsea books by Ursula K. Le Guin
The Summer Birds by Penelope Farmer
The Owl Service by Alan Garner
the Animorphs series by Katherine Applegate

Hope this rings a bell with someone!

 

[zaelyel]

Jennifer Roberson: The Chronicles of the Cheysuli ?

 

[Ms Atoz]

Sadly the Cheysuli books are too recent. She's positive she read these books back in the late sixties or early seventies. But thanks for the suggestion!