Did a brief Google and found an alleged hybrid written up in The Wilson Quarterly a quarter century ago. ID was done from a skin so the burning question Greg and I are faced with - can a bird with largely Black-billed field marks sing the song of a Yellow-billed?
>From: "Gregory R. Askew" <[log in to unmask]>
>Date: Fri Jun 10 09:20:25 CDT 2005
>To: [log in to unmask]
>Is there any evidence of the black-billed and yellow-billed cuckoo hybridizing?
>Saw two cuckoos today with Tom Barber at one location in his birding block, one
>which sounded like a yellow-billed and had some slight masking behind the eye
>but also had a buffy neck like a black-billed. The sighting was brief and the
>bird's beak was blocked from view by leaves, so we didn't have the opportunity
>to confirm that obvious field mark.