In May, we look forward to the return of both species of cuckoos; we love to see these birds flying past with their long tails and pointed wings. Cuckoos are secretive, so spotting them and making an identification only by their bill color is difficult. Both can be found in the same habitats which adds some complication to ID, but there are a couple other good ways to tell them apart.
Yellow-billed Cuckoos have large white spots on their tail feathers while Black-billed Cuckoos have solid brown tails. Learning their calls is probably the best way to identify them—the black-billed song is faster than the yellow-billed song. When visiting wetlands in spring, you may hear a cuckoo-like call and at first think that you are hearing a cuckoo; however, a male Least Bittern’s song has a similar sound. In these instances, the Merlin Bird ID app can be a helpful tool. When we heard a cuckoo-like call this spring from a cattail marsh, Merlin quickly identified it as a Least Bittern.
Like their counterparts across the world, both Yellow-billed and Black-billed Cuckoo will occasionally lay their eggs in the nests of other cuckoos or other species of birds, making them intraspecific brood parasites. Cuckoos have very flimsy nests and often nest less than 10 feet from the ground.
A Yellow-billed Cuckoo, with prominent white spots on the tail (photo by Lesley Haven).
Sam Robbins wrote in Wisconsin Birdlife (1991) that Black-billed Cuckoos were a fairly common summer resident throughout the state while Yellow-billed Cuckoos were a fairly common summer resident in the southern part of the state and a rare summer resident further north.
In the Wisconsin Breeding Bird Atlas II (2015–2019), that pattern remained. In Columbia County, black-billed were confirmed breeding in three atlas blocks and probable in four more; yellow-billed were confirmed breeding in five and probable in eight. Usually, confirmations are from seeing adults carrying food back to nests. Mark Martin and longtime volunteer Brand Smith had an interesting observation at the tail end of the WBBA II project in August 2019:
“While walking back with the canoe we stopped to rest, and Brand saw an adult Black-bill Cuckoo very close to us. We had an excellent look at it within 30 feet in the open a couple of times. We followed it as it flew short distances for about 10 minutes. Then Mark saw it fly and one other cuckoo (had not seen) follow it to the east. Then immediately we heard a black-billed cuckoo calling where we saw the first one. Within a minute we had one call a few notes to the west (close) of us for a family of 4. HARD TO BELIEVE WE FINALLY CONFIRMED A FAMILY OF BLACK-BILLED CUCKOOS!!!!!!!”
A Yellow-billed Cuckoo died after colliding with a window on the UW-Madison campus in spring 2024, reported by the Bird Collision Corps program (photo by Aibigail Punam).
According to the Cornell Lab of Ornithology, Yellow-billed Cuckoo populations declined about 34% between 1966 and 2019. One of the biggest threats facing the species are collisions with buildings and other human-created structures during long distance migrations. Brenna Marsicek, Southern Wisconsin Bird Alliance’s director of outreach and coordinator of the Bird Collision Corps program, reports that just this spring, volunteers in the program found two dead Yellow-billed Cuckoos that collided with windows in Madison. It is sad that these two individuals began a long journey north from South America and died before they could reach their breeding grounds, which likely weren’t much further.
A Black-billed Cuckoo feeds from a web spun by eastern tent caterpillars on a tree (photo by Andy Reago and Chrissy McClarren).
Black-billed Cuckoos are of high conservation concern, points out the Cornell Lab, with their populations cumulatively dropping 67% between 1970 and 2019—almost double that of the yellow-billed. Their numbers fluctuate based on the availability of food sources, like cicadas and caterpillars, but overall, loss of habitat and use of pesticides are likely major contributors to the overall decline of these cuckoos.
Eastern tent caterpillars, a favorite cuckoo food, prefer plants in the rose family (Rosaceae) such as cherry, apple, crabapple, and plums. Caterpillars can also be found in lower numbers on willows, maple, oak, and poplar. At Goose Pond Sanctuary, wild plum clones are expanding and additional wild plums are being planted. We are also planting wild plums at our cabin. We hope this will result in a steady food source for the cuckoos!
Written by Mark Martin and Susan Foote-Martin, Goose Pond Sanctuary resident managers
Cover image by Andy Reago and Chrissy McClarren. A Black-billed Cuckoo with a long brown tail and red eye-ring perches on a the end of a branch.
