Cuckoo, Yellow-billed or Black-billed?

Yellow-billed Cuckoo photo
Yellow-billed Cuckoo
Strikingly unique in flight, skulking and secretive in the trees, cuckoos are often difficult to observe.  By far, the majority of Florida's cuckoos are Yellow-billed.  Bill and eye ring color are readily apparent on a perched cuckoo, when seen well.  But what of the rest?  Most cuckoos flash across the trail and/or disappear among the foliage; no way to tell if they are Yellow-billed or Black-billed.

Maybe not.  In good light and at close range, flying cuckoos are more easily separated than you might think.  Flying Yellow-billed cuckoos show a distinct rufous flash in the primaries while Black-billed cuckoos have very little or no rufous.  Note:  Mangrove cuckoos (limited range in south and southwest Florida) also lack rufous in the primaries.  Upper parts of Yellow-billed cuckoos are noticeably warm brown.  Black-billed cuckoos show a colder, grayer, tone.  Both species have white tips on the tail feathers, but these are more prevalent on Yellow-billed.  At close range, underpart coloration is surprisingly helpful.  While searching for Mangrove cuckoos in the keys, I was struck by the immaculate white underparts of Yellow-billed cuckoos, and by how many Yellow-billed cuckoos are in the keys.  Black-billed cuckoos have more dull, off-white colored underparts.

I have seen about a dozen Black-billed cuckoos in Florida.  Only two were perched, allowing me to observe the diagnostic bill and eye ring.  I first recognized a Black-billed cuckoo in flight at Sebastian Inlet State Park.  I was struck by the lack of rufous in the wings and the drab upper parts.  The first thing I notice on flying cuckoos is the flash of rufous in the wings, or lack thereof.  Next is spotting on the tail feathers.  Many flying cuckoos are heading away from me, making it impossible to see the underparts.  Underpart coloration, if you can see it, is a surprisingly good mark and a useful supporting characteristic.  Altogether, these traits give Yellow-billed cuckoos a distinctly more contrasty look than the more uniform appearance of Black-billed cuckoos.  Cuckoos often flush at close range, allowing close observation, if only for an instant.  With some practice and good conditions (sun at your back, bird in good light), wing flash, upper part coloration and tail spotting can be noted quickly.  Cuckoos flying in the shaded canopy or toward the sun are probably best left unidentified or with the safe assumption of Yellow-billed.

The next time a cuckoo flies by, look at the wing tips, look at the tail, assess the tone of the upper parts, and the underparts, if you can.  You will see lots of bright, contrasty Yellow-billed cuckoos.  Keep looking; eventually one of them will be a dull, boring, old Black-billed!