Avian visitor is often heard, seldom seen
One of Minnesota's more interesting summertime avian residents has recently arrived here.
Often heard and less frequently seen, I once again heard the telltale call before catching a fleeting glimpse of it: the black-billed cuckoo. Indeed, audible observations are commonplace for those wishing to log this bird on their species checklist.
It's my opinion that not many people are even aware that such a bird exists, let alone knowing from what species of bird such an interesting vocalization comes from. The cuckoo's call is, after all, the inspiration of the familiar cuckoo clock's punctual (and vocal) little bird that plays peek-a-boo every hour.
Here in North America, cuckoos belong to an interesting family of birds comprised of only six species and three genera. Three different species of cuckoos (mangrove, yellow-billed, and black-billed), two species of ani (groove-billed and smooth-billed), and the greater roadrunner all belong to the family Cuculidae.
Black-billed cuckoos are unremarkable-looking birds that are somewhat easily overlooked. Slender and long-tailed, these otherwise large 12-inch songbirds spend most of their time within the dense foliage of thickets and woodlands hunting for food.
Males and females are indistinguishable from one another. Off-white below and a soft brownish-grayish above, these bi-colored birds' most distinguishing features - aside from their unique call - are their black, de-curved beaks, white tail-spots and red orbital rings. The juveniles of the species are drabber overall and have greenish eye rings instead of red.
The cuckoo's call shares similarities with that of the saw-whet owl, mourning dove, least bittern and pied-billed grebe. A stretch, perhaps, but I can liken the calls of black-billed cuckoos to no other. That said, the cuckoo's whistle, which is frequently delivered in repeated triplicate arrangement (po-po-po . . . po-po-po . . . po-po-po), is unmistakable once heard and put to memory.
Preferred habitats for cuckoos are forests of dense deciduous trees and shrubs. It is within these environments where they actively hunt and capture their favorite food - caterpillars. And while the range of yellow-billed cuckoos includes southern Minnesota, chances are that any cuckoo heard or observed here in the Northland will be a black-billed cuckoo.
Cuckoos seem to disappear into obscurity during most of their summer stay, but in years when caterpillar populations are especially high, you may also notice an abundance of cuckoos. During those years when hoards of forest tent caterpillars work to defoliate aspen forests by consuming the leaves of the trees, cuckoos will be right there hungrily gulping down the fat, juicy and nutritious caterpillars.
Black-billed cuckoos consume many different species of caterpillars, as well as other insects, but they favor moth and butterfly larvae above all other invertebrates. In fact, cuckoos eat both hairy and hairless caterpillars, including the spiny ones too.
As strange as it sounds, and because the spines of these latter caterpillars tend to stick to the lining of a cuckoo's stomach, cuckoos have the astonishing ability to shed their stomach lining every so often in order to rid themselves of accumulating spines. Other foods that cuckoos will eat are spiders, small mollusks, fish and wild fruits and berries.
Another interesting fact about cuckoos is that the bird is a surprisingly rapid nester. Only 17 days pass from the time when an egg (usually two to four) is deposited in the nest bowl to the time the young nestlings fledge. Yet, despite their reproductive strategy, most pairs of cuckoos raise only one brood per year. To compare, many other species of neo-tropical migrants raise two or more broods a nesting season.
Although not as frequently as do some of its cousins and Old World relatives, black-billed cuckoos occasionally "dump nest" or parasitize other birds' nests by laying eggs inside these "host" nests and leaving. Other species of birds, such as wood ducks and hooded mergansers, not to mention brown-headed cowbirds, do this as well.
The cuckoo nest is normally built of twigs in the lower parts of deciduous trees and shrubs. Apparently because of their irregular nesting habits, some eggs tend to become partially incubated during the egg laying process before the entire clutch is deposited.
This sometimes results in asynchronous hatching. From the literature, one Nova Scotia nest that was observed in 1945 contained four nestlings with the smallest youngster half the size of its largest nest-mate.
The black-billed cuckoo has even been acclaimed as a predictor of rain. These avian forecasters are called "rain birds" or "rain crows" by some people. According to those who believe, cuckoos have the tendency to vocalize more intensely prior to the onset of rain showers.
Cuckoos are interesting birds that are frequently heard, but less seen. During some years, perhaps because of low abundance of caterpillars, you might not observe a single cuckoo. Nevertheless, black-billed cuckoos travel all the way from South America to Minnesota each spring in order to spend a few months raising their young.
Though you probably will only hear the black-billed cuckoo's call, keep searching the thickets for a climbing, fluttering and hopping cuckoo-bird gleaning insects from branches and leaves as you get out and enjoy the great outdoors.
Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at firstname.lastname@example.org.