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Yellow-billed Cuckoos

Maureen Eiger

Natural History

Yellow‐billed Cuckoos (YBCUs) (Coccyzus americanus) are not often seen in the wild since they are
fairly cryptic in the leaves of trees. Unless spotted flying from tree to tree, they are more often heard
calling, especially when it is humid outside or about to rain. Their nickname is “rain crow” by
some birders. Yellow‐billed Cuckoos are something of an enigma because they are quite secretive.
Reports written by various well‐known observers when compared to each other have conflicting
information or missing information on their breeding behavior and how their young develop.
More research, record keeping, and observations are needed to clarify the conflicting observations
about the YBCUs life cycle, breeding habits, and the effect that loss of habitat and man‐made dis-
turbances have on their survival.
Western YBCUs are generally listed as a species in steep decline, and the birds are listed as
endangered or near threatened on several U.S. state bird lists. In October 2014, YBCUs were listed
by U.S. Fish and Wildlife Service as “threatened,” though this designation seems to have a lot of
controversy behind it. According to the American Bird Conservancy (2019), this species has been
reduced to fewer than 500 breeding pairs and is largely absent from most of its historical range.
Adult YBCU are slender‐bodied and long‐tailed birds about 12 in. (30.5 cm) long, with grayish
brown contour feathers on their head, nape, back, and top surface of the tail and white feathers on
their cheeks, throat, and belly. Adults weigh 50–65 g, and have short blueish‐gray legs with zygo-
dactyl toes. Their bills are slightly downward‐curved toward the tip and the lower mandible is
yellow‐colored when mature. Rufous wing coloring is evident as soon as their chicks grow feath-
ers. The birds also have large oval white spots against black on the undersurface of its grayish
brown tail feathers.
Fledgling YBCUs look like miniature adult birds but with shorter beaks and tails. They have very
fluffy (not sleek) feathers. It’s easiest to identify a young YBCU when it opens its mouth. The bird
has a black‐tipped tongue and white bumps on the roof of its pinkish mouth. The “white bumps”
are often mistaken for a fungus/yeast infection but are normal for the bird and may aid in swallow-
ing spiny caterpillars or help lock onto the adult’s beak when being fed. The easiest way to tell the
difference between a young YBCU fledgling vs a Black‐billed Cuckoo of similar age is by the rufous
coloring on the YBCUs wings.

Hand-Rearing Birds, Second Edition. Edited by Rebecca S. Duerr and Laurie J. Gage.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.