Jim McCormac wrote a blog post/newspaper article about cuckoo life history that's definitely worth a read. The cuckoos have very distinct calls and we have been hearing the yellow-billed "po" call and the black-billed "cu, cu, cu, cu" in the woodlands near us.
Pardon our amateur video skills, but watch the cuckoo look for the caterpillars and eat them:
Yellow-billed and black-billed cuckoos are both here right now in Ohio and both share similar diets. Cornell Birds says this about the black-billed cuckoo diet:
"The Black-billed Cuckoo is a notorious consumer of caterpillars, with a demonstrated preference for noxious species, including the eastern tent caterpillar (Malacosoma americanum), fall webworm (Hyphantria cunea), and larvae of the gypsy moth (Lymantria dispar). Observations of cuckoos consuming 10-15 caterpillars per minute are testimony to the great service this species provides in forests, farms, and orchards. Stomach contents of individual cuckoos may contain more than 100 large caterpillars or several hundred of the smaller species. The bristly spines of hairy caterpillars pierce the cuckoo's stomach lining giving it a furry coating. When the mass obstructs digestion, the entire stomach lining is sloughed off and is regurgitated as a pellet."
As soon as the caterpillars felt threatened by the cuckoo in our yard, they dropped from the leaves but still remained attached via a strand of silk. If you look closely at the photo below you can see at least four strands of silk on the left side.
The cuckoo repeatedly attacked different groups of caterpillars and some were physically knocked off the leaves before they could drop with their silk attached.
After the cuckoo moved on we went over to the site and observed at least 50+ and probably more caterpillars dangling from silk and crawling on the ground. The lucky ones attached to the tree via their silk had the arduous, but attainable task of climbing their way back up:
Those knocked to the ground without silk kept climbing up the tallest plants around in hopes of reaching their food plant. Alas, many days later and dozens are still wandering about here and there since the lowest leaves of the black walnut are at least 4-5 feet off the ground. Of course, I help some back up to the leaves when I find them in the hopes that they will reach adulthood. Luckily, hickory tussock caterpillars are generalists and eat a wide array of plants so they should find something else they like to eat before too long or they just might become another tasty meal for the local cuckoos - a bird we are so happy to have around.