You may never have seen a Yellow-billed Cuckoo, but most likely you have heard the call of this fascinating bird on a hot summer day.
The call sounds exotic, and unlike the trilling melodies of other summer birds. The knocking call of the elegant Cuckoo is reminiscent of a person rapping on a door with a metal doorknocker. Alternately, the Cuckoo may produce a longing coo that is equally foreign to our ears.
You may look up and around to locate where the sound is coming from, but it can be hard to locate a bird that stands as still as a sentinel, deeply concealed in the foliage. Unlike the hyperactive Warblers that flit from branch to branch, the Yellow-billed Cuckoo is a master of patience; it perches its long, slim self on a well-hidden branch, and waits. When its prey is located, it’s a quick pounce, and then a giant hairy caterpillar is snapped up.
Generally, the cuckoo doesn’t rapidly gobble up its prey, but appears to thrash it around with its beak, perhaps to remove some of the stinging hairs, or just to give the large prey a bit of tenderizing in order to maneuver swallowing the large meal. Many birds cannot tolerate the stinging protective hairs of these large caterpillars, but the cuckoo has evolved an efficient mechanism to handle this difficult meal rather ingeniously. The caterpillar is swallowed whole, along with its protective spiny hairs. The hairs of the caterpillars remain in the stomach of the bird, but periodically, the Cuckoo will shed its entire stomach lining and grow a new replacement.
This behavior reminds me of the way we swipe out the lint filter in a clothes dryer. As an added benefit to this adaptation, when the bird sheds its stomach lining, the shed removes the parasites that inhabit the inner layer of the stomach epithelium.
The diet of the Yellow-billed Cuckoo is beneficial to the forest it inhabits. Cuckoos predate many of our most destructive caterpillars. The population of Yellow-billed Cuckoos will often correspond to the irruptions of caterpillars in a given year. These feasts or famines have rather interesting behavioral consequences for the bird.
Cuckoos are known for their erratic parenting techniques. They build haphazard nests of a handful of thrown together twigs, and have been know to lay eggs in other bird’s nests. You are perhaps thinking that these are the neighborhood freeloaders, not like the dreadful Cowbirds who force other birds to raise their offspring. But it is a matter of urgency. When there is a significant caterpillar irruption, the food supply for the Cuckoo has a precipitous upturn, and the female is ready to lay her eggs in very short order. The nest is simply not ready for the early arrivals. Sometimes, the nursery isn’t finished when nature calls. Unlike the destructive Cowbird, the Cuckoos are very good parents who bring food to the host bird’s nest, and often feed both their own offspring, as well as the host bird’s offspring. What perfect guests!
The environmental consequences of human development are having disastrous effects on Yellow-billed Cuckoos in the West. In states like Colorado where flooding rivers are frequently tamed by dams, the Cottonwood trees that thrive on flooded lands are disappearing. The Cottonwood tree is host to many caterpillar species, and hence host large numbers of Cuckoos. The Yellow-billed Cuckoo is threatened so severely that the species is almost totally extirpated in many western states where it once thrived. As trees such as Russian Olive now replace the flood requiring Cottonwoods, there is no food source to support the Cuckoo. Here in the South, we have no threat to the species, but the national picture is more dire. It is estimated that 90 percent of the western population has disappeared. The riparian forests required by this species no longer exist. On April 10 the US Fish and Wildlife Service opened a comment forum to accept observations and suggestions, with the aim of adding this species to the list of “threatened species” under the Endangered Species Act.
Here in North Carolina you have a great opportunity to see Yellow-billed Cuckoos at Mason Farm Preserve, and at Jordan Lake. The bird is sometimes called the “Thunder Crow” as they are often heard calling on the hottest summer days as a presage to a thunderstorm. They are easiest to locate when you find a tree that has a lot of warbler activity. You will notice all sorts of flitting birds, and if you look very carefully, you may notice a long, yellow-billed bird with a brilliant white breast, sitting erect and motionless on a branch. The uppers are soft gray with rufous wing patches, and the tail is spotted with crisp white ovals; a beauty for sure.
The plight of the Yellow-billed Cuckoo comes down to the same old story. If we can be stewards who preserve our riparian land, the wildlife will preserve the trees, and clean the water for us. We just need to stop “improving” the environment.
Mary Sonis is a naturalist, photographer and writer in Carrboro. You can reach her at firstname.lastname@example.org