If you live in one of the areas subject to this year’s biblical plague of gypsy moth caterpillars, then you might be interested in this week’s bird report. Many parts of southeastern Massachusetts are getting hit hard by another major outbreak of this invasive species, originally introduced from Europe in the 1860s.
Gypsy moth populations are typically held in check by a fungus, but a dry spring kept the fungus at bay and helped cause this summer’s outbreak. The outbreak is patchy, with some areas looking normal, while others have an eerie, mid-winter feel, as the light filters unsettlingly through the skeleton trees. Many folks are distraught about their bare trees, but they should leaf out again now that the caterpillars have begun to pupate and develop into the adult moths.
But while you’re sobbing quietly because it looks like February in your yard and you are up to your armpits in caterpillar droppings, there are some local residents who are excited about the infestations. I am of course talking about cuckoos!
Both Yellow-billed and Black-billed Cuckoos are having a banner year in Massachusetts thanks to the superabundance of caterpillars. Cuckoos are caterpillar specialists, and unlike other birds, are able to eat even the hairiest and spiniest of caterpillars, including gypsy moths and tent caterpillars. Their secret lies in a strange physiological adaptation: when the lining of their stomach becomes a pincushion of caterpillar hairs and spines, they can regurgitate it as a pellet and start over with a fresh lining. Both species have been found with hundreds of hairy caterpillars in their stomachs at one time.
Cuckoos are among my favorite birds. They check several key boxes for species interestingness – mysterious, hard to see, uncommon, and just plain weird. In addition to the stomach regurgitating trick, they have some of the fastest developing chicks in the bird world. They can go from naked hatchling to fully feathered chick in a matter of hours, and from egg to free flying juvenile in 17 days, which is a blink of an eye in avian development terms. Even a chickadee takes close to a month from egg to fledgling. Those caterpillars must be full of avian growth hormone.
If that wasn’t weird enough, they sometimes lay their eggs in the nests of other species, a behavior known as nest parasitism. European cuckoos, the ones the famous clocks are based on, are much more frequent and accomplished nest parasites.
Our North American Cuckoos seem to do it when they feel like it, though they are normally attentive parents to their freakishly fast-developing chicks. Hunch-shouldered and long-tailed, cuckoos seem slow and ungainly in flight. They nevertheless migrate as far as the southern half of South America each fall, so they are obviously more athletic than they seem.
As weird as they are, let’s hope you have some cuckoos in your yard helping to keep the leaf-munching hordes at bay. Speaking of which, the entomologically correct term for caterpillar droppings is “frass.” Feel free to use that new word to impress your neighbor later while you’re sobbing together under your bare trees.
