Yellow-Billed Cuckoos Eat More Than Teenagers Do

  • A detail shot of the yellow-billed cuckoo and its namesake beak. Photo: Luke DeGroote

  • A yellow-billed cuckoo being banded at Powdermill Nature Reserve. Photo: Luke DeGroote

August 7, 2015

Of all the songbirds in eastern North America, cuckoos probably have the craziest stomachs. In an eating contest, ounce for ounce, yellow-billed cuckoos would put hungry teenagers to shame. They can eat more than 100 caterpillars in less than 10 minutes. Pound for pound, that's the equivalent of a 15-year-old eating 10 pizzas.

Prickly caterpillars are like the little porcupines of the insect world. They’re covered in tiny hairs stiff enough to pierce the stomach lining, so most birds won’t touch them. Cuckoos, on the other hand, swallow them whole until their stomach becomes covered in a dense mat of course noxious hairs. Then the cuckoo simply sheds its entire stomach lining, hairs and all, and regurgitates it as a packet—much like a cat coughing up a hairball. The cuckoo is left with a fresh stomach lining ready to digest more hairy caterpillars.

This may seem cuckoo, but it gives them a distinct advantage when it comes to raising lots of little cuckoos. During some summers, there’s a boom in the population of hairy caterpillars. With all that food, and both parents feeding their young, the chicks grow fast and have a very short nesting cycle. Cuckoos can raise two or even three broods of chicks in a season. They can leave the nest in as little as 19 days after the parents picked up the first stick to build it.

Cuckoos are large birds—almost the size of a blue jay. But they’re rarely seen. They spend most of their time skulking through scrub or young forests with dense understories. They have long tails, clean white bellies, with curved bills that are black and, of course, yellow. Spotting one may be harder than hearing one. You can listen for a soft cooing sound.

You may even hear their “ka-ka-ka-ka-ka-kow-kow-kowlp-kowlp-kowlp-kowlp,” making you think you somehow wandered from the eastern US to the tropics. 

If you do get lucky and see a yellow-billed cuckoo, it will probably be gobbling down the last of the big hairy caterpillars—fattening up for its long fall flight to Central America.

Bird songs and calls for the audio recording of this segment are provided by the Macaulay Library at the Cornell Lab of Ornithology, and recorded by James W. Kimball and Wilbur L Hershberger.