On Rick Robinson's blog, J. F. Norris made this comment.
"A parrot squawking out a mysterious phrase occurs much more frequently in mystery fiction than I ever would’ve imagined. There’s Death in Swaythling Court, Murder on Wheels, The Chinese Parrot, and this one [The Case of the Perjured Parrot by Erle Stanley Gardner]. I’m sure there are more.
Can anyone come up with more for Rick? Such a strange device to be repeated. But as the only bird (or animal) that speaks, too good to ignore?