When describing the Black-billed Cuckoo, most authors cannot resist the temptation to combine this species with the very similar Yellow-billed Cuckoo. Both birds are about the same size. Both are reclusive and frequently difficult to see, in spite of the fact that they may be calling nearby. Both favor shrubby edge habitats, although the Black-billed species tends to prefer drier thickets. The list of similarities goes on and on.
So, if you happen to see a cuckoo sitting on a branch, how do you tell to which species it belongs? First, they don’t call them yellow-billed and black-billed for nothing. The bill of the former is mostly yellow while that of the latter is obviously black. Suppose you cannot see the bill that well, however. Your next best bet would be to check out the bird’s tail. The Yellow- billed Cuckoo has large white spots, while those on the tail of the Black-billed Cuckoo are smaller.
Chances are, however, that you are going to hear a cuckoo before you see one. (if you ever do see one!) So, it would be best to learn to distinguish between their calls.
Unfortunately, neither sounds like a clock. That would be the European species. The Yellow-billed Cuckoo’s call has been described as “ka ka ka…kowp kowp kowp”. The Black-billed goes “cu cu cu”. Short, sweet and all in one pitch. Supposedly, cuckoos sing more just before a rain shower. For that reason, they were referred to at one time as rain crows.
Black-billed Cuckoos spend the winter in South America and the summer in the Northeastern United States and Southeastern Canada. Although arriving back on their breeding grounds in late April to mid May, nesting may not begin at once. In fact, there is a wide variation in nesting dates from year to year. This may be due to the abundance (or paucity) of the insects that the birds feed to their young.
Once the urge finally hits them and the mostly monogamous pairs form, both sexes participate in nest building. These nests are frequently described as being unkempt and flimsy platforms lined with soft plant material. They can frequently be sited anywhere from to two to eight feet off the ground.
Egg-laying follows. There are usually two or three of these, however, in times when caterpillars are in particular abundance, clutches as large as eight have been recorded. On the other hand, if the insect food source suddenly crashes or the cuckoo’s own nest is destroyed (or falls apart) before some eggs are laid, the Black-billed Cuckoo may be inclined to dump them in the nests of other birds at hand. These have Yellow Warbler, Chipping Sparrow, Eastern Wood-Peewee, Northern Cardinal, Cedar Waxwing Gray Catbird, Wood Thrush, American Robin, or even Yellow-billed Cuckoo.
The Black-billed Cuckoo should not be compared to the Brown-headed Cowbird, however. It generally raises its own young in its own nest. Unlike most bird species, when the young hatch, the Black-billed Cuckoo makes no effort to remove the egg shells from the nest.
Black-billed Cuckoos are primarily insect eaters. They consume large quantities of caterpillars, cicadas, grasshoppers, tree crickets, etc. They have also been known to eat tree frogs. Fruits may be added to the diet in the summer and fall months. These include elderberry, mulberry, and wild grape.
What cuckoos are most famous and appreciated for, however, is the fact that they specialize in eating hairy caterpillars. Many of these are injurious ones. Gypsy Moth, Forest Tent Caterpillar, and Canker Worm are all on the menu.
What happens to all the hairs? The cuckoos do not digest them. Rather, the hairs accumulate over time, building up little masses in their stomachs. At some point, this gets to be a bit much and the birds shed their whole stomach linings and grow new ones. (Yuck!) How often this occurs is a matter for some graduate student in Ornithology to figure out some day.
Black-billed Cuckoos usually only nest once in a season. After the nestlings fledge, the adults fall silent. Migration takes place at night in September and October, the ultimate destination being South America.
Both cuckoo species are masters of what is called countershading. This is a sort of camouflage where the bird is dark on top and white underneath. It tends to obscure its outline, making it less visible to predators.
Cuckoos are probably more abundant here now than in the past. (That’s nice for a change.) This is no doubt due to the increase in edge habitats facilitated by human settlers. Land and forestry practices may have also encouraged caterpillar irruptions. A group of cuckoos (Not that you are probably ever going to see one) is called a “cooch” or an “asylum” As far as can be determined, Audubon never ate one.