Black-billed Cuckoo

The monotonous “cu cu cu” call of the Black-billed Cuckoo is often the only sign that the species is in the vicinity, since it tends to remain motionless in dense vegetation. Anecdotally cuckoos were believed to call more often before rain, resulting in the colloquial name “rain crow,” but this correlation has not been investigated. They are often heard at night, including during migration. Listening to the night sky in late May or early June is often a good way to hear your first cuckoo of the year!

Cuckoos are famous for being specialists on large hairy caterpillars such as Spongy Moth, fall webworm, and tent caterpillar. The hairs of these insects are irritating and serve as a defense against predators, even penetrating the stomach lining after being eaten, but this does not deter the Black-billed Cuckoo. If the number of hairs builds up to the extent that they interfere with digestion, the cuckoo will regurgitate its stomach lining to remove them – much like an owl coughs up a pellet with the bones and fur of its rodent prey. When preferred prey are less abundant, cuckoos consume other large insects such as cicadas, grasshoppers, and butterflies. There are even records of them capturing and eating the toxic Monarch Butterfly.

Although Black-billed Cuckoo populations go up and down with their prey, the overall trend across the species’ range has been a decline. Although little studied, this decline is believed to be partly due to habitat loss, especially the dense Shrublands the species often uses for nesting. This loss of shrubland can result from forest maturation, development, or over-browsing by high deer populations. It is also possible that control of caterpillar pests has had both direct and indirect effects on cuckoos. Finally, there is evidence that cuckoos are disproportionately subject to collisions with towers and buildings.