05/09/2026
Happy World Migratory Bird Day! From their strange calls to their preference for caterpillars, cuckoos are some of the most fascinating birds to breed in and pass through the EBBA region each spring and summer. Large numbers of tent caterpillars near your net lanes may attract these amazing birds, which are specially adapted to feed on hairy caterpillars that many other species avoid. Cuckoos can even shed the lining of their stomachs once it becomes clogged with irritating caterpillar spines and hairs, and both Yellow-billed Cuckoos (YBCU) and Black-billed Cuckoos (BBCU) are capable of eating more than 100 caterpillars in a sitting if there is an abundance! Letâs take a closer look at the two species that EBBA region banders may encounter during spring and summer banding.
There are several differences between the two species, with the most obvious being bill color. Adult YBCU (right side) have an almost totally yellow mandible, while BBCU (left side) have a completely black/gray mandible. The red orbital ring in adult BBCU is another field mark separating them from the gray orbital ring in adult YBCU. However, hatch-year (HY) and second-year (SY) BBCU can show a yellow-green to gray orbital ring, while the young YBCU usually have a yellow orbital ring.
YBCUs display a large, diffuse rufous patch on their primaries and secondaries, while BBCUs have more uniformly brown wings. In addition, YBCUs have large, bold white spots at the tips of the rectrices (tail feathers). BBCUs also have white tail marks, but they are much smaller and appear only as thin slivers at the ends of the rectrices.
