The yellow-billed cuckoo, with its western subspecies, covers practically all the United States and some of southern Canada. It is mainly a bird of the Austral Zone, being much commoner in the Southern States than in the northern portions of its range. In New England it is not so common as the black-billed cuckoo, though in some seasons it seems to be a familiar bird. Originally it was probably a woodland bird, but, like many other species, it has learned to frequent the haunts of man, where it is not molested and where it finds an abundant food supply in our shade trees, orchards, and gardens. Its favorite haunts are still the woodland thickets, where the tree growth is not too heavy, brush-grown lanes, shady roadsides, dense thickets along small streams, and apple orchards in rural districts. In dense, heavy woods it is seldom seen.

Nesting.--Unlike the European cuckoo, both of our North American species usually build their own nests and rear their own young, though they are very poor nest builders and are often careless about laying in each other's nests or the nests of other species. Major Bendire (1895) gives the following very good account of the nesting habits of the yellow-billed cuckoo:

The Yellow-billed Cuckoo is one of the poorest nest builders known to me, and undoubtedly the slovenly manner in which it constructs its nest causes the contents of many to be accidentally destroyed, and this probably accounts to some extent for the many apparent irregularities in their nesting habits. The nests are shallow, frail platforms, composed of small rootlets, sticks, or twigs, few of these being over 4 or 5 inches in length, and among them a few dry leaves and bits of mosses; rags, etc. are occasionally mixed in, and the surface is lined with dry blossoms of the horse-chestnut and other flowering plants, the male aments or catkins of oaks, willows, etc., tufts of grasses, pine and spruce needles, and mosses of different kinds. These materials are loosely placed on the top of the little platform, which is frequently so small that the extremities of the bird project on both sides, and there is scarcely any depression to keep the eggs from rolling out even in only a moderate windstorm, unless one of the parents sits on the nest, and it is therefore not a rare occurrence to find broken eggs lying under the trees or bushes in which the nests are placed. Some of these are so slightly built that the eggs can be readily seen through the bottom. An average nest measures about 5 inches in outer diameter by 1 1/2 inches in depth. They are rarely placed over 20 feet from the ground, generally from 4 to 8 feet upon horizontal limbs of oak, beech, gum, dogwood, hawthorn, mulberry, pine, cedar, fir, apple, orange, fig, and other trees. Thick bushes particularly such as are overrun with wild grape and other vines as well as hedgerows, especially those of osage orange, are most frequently selected for nesting sites. The nests are ordinarily well concealed by the overhanging and surrounding foliage and, while usually shy and timid at other times, the Yellow-billed Cuckoo is generally courageous and bold in the defense of its chosen home; the bird on the nest not infrequently will raise its feathers at right angles from the body and occasionally even fly at the intruder.

Of five Massachusetts nests, of which I have notes, the lowest was only 2 feet above the ground in some bushes, and the highest was 12 feet up in a crotch near the top of an oak sapling in a swampy thicket near a brook. Owen Durfee mentions in his notes a nest 5 feet up in a juniper on the edge of a swamp. The others were at low elevations in thickets along brooks.

A. D. DuBois has sent me his notes on five Illinois nests; one of these was on the end of a branch of an apple tree, 8 feet from the ground, near a country schoolhouse; this nest contained 3 eggs of the cuckoo and a robin's egg. Another was near the end of a branch of an osage-orange hedge, 10 feet up; still another was in an isolated clump of willows, between a field and a pasture, 6 feet from the ground.

But cuckoos do not always nest in such low situations; there are several records of their nesting well up in elm trees. Grant Foreman (1924) tells of a pair that nested on his place in Muskogee, Okla., for one or two years, high up in an elm tree; he says: "The next year after nesting in this inaccessible place, they built their nest in a little elm tree in the parking, on a low limb overhanging the curb on a asphalt street where hundreds of automobiles were passing every day, and here in this exposed, noisy place they raised a brood of young. This year they built their nest in a little hackberry tree in the parking along the side of my lot; but here also the nest was on a low limb overhanging the curb on a paved street, and the ice wagon stopped every morning directly under this nest, which was so low down that the driver might have put his hand in it."

George Finlay Simmons (1915) mentions a nest that he found near Houston, Tex., on the horizontal limb of a young pine near the edge of some woods. He says of it: "The nest was a slight platform about eleven feet up, through which I could see with ease; it was composed of small pine twigs, about an eighth of an inch in diameter and averaging six or eight inches long, and was much more concave than I had expected. This shallow saucer was neatly, though quite thinly lined with a few pine needles, a small quantity of Spanish moss and several tiny buds."

George B. Sennett (1879) says that in the Lower Rio Grande region of Texas "ebony trees near the ranch, mesquites among the cactuses, thorny bushes in open chaparral, and open woodland, were favored breeding places."

Wright and Harper (1913) found a well-made nest in Okefinokee Swamp, in a tupelo tree at the margin of the Suwannee. "It was placed in a cluster of mistletoe on a horizontal branch four feet above the water, and consisted of sticks interwoven with Spanish 'moss' (Tillandsia usneoides)."

Dr. Harry C. Oberholser (1896) gives the measurements of four nests; the average height of the nests was 4 inches, and the greatest outside diameters averaged 7.63 by 6.25.

Both species of North American cuckoos often lay their eggs in each other's nests. The eggs of the yellow-billed cuckoo have been found several times in nests of the robin and catbird. H. P. Attwater (1892) writes: "In 1884 I found a Dickcissel's nest which contained five eggs and one Yellow-billed Cuckoo's egg. The next year some boys brought me three Black-throated Sparrow's eggs and one Yellow-billed Cuckoo's, from the same field, which they said they found all together in one nest." J. L. Davison (1887) says: "I also found a nest of Merula migratoria, taken possession of by Coccyzus americanus before it was finished, which was filled nearly full of rootlets; and in this condition the robin laid one egg and the Cuckoo laid two and commenced incubation, when a Mourning Dove (Zenaidura macroura) also occupied it and laid two eggs and commenced incubation with the Cuckoo. I found both birds on the nest at the same time, when I secured nest and eggs. The eggs of the Robin and Cuckoo were slightly incubated; those of the Mourning Dove were fresh."

Bendire (1895) adds the wood thrush, cedar waxwing, and cardinal to the list of birds that have been imposed upon, and says: "Such instances appear to be much rarer, however, than those in which they interlay with each other, and the majority of these may well be due to accident, their own nest having possibly been capsized, and necessity compelled the bird to deposit its egg elsewhere. Such instances do occur at times with species that cannot possibly be charged with parasitic tendencies."

Marcia B. Clay (1929) thus describes the cuckoo's method of gathering twigs for her nest:

Flying into an adjacent apple tree containing a considerable quantity of dead material, the Cuckoo landed on a limb, selected a dead twig, and grasping it in her bill bent it back and forth until it snapped from the limb, whereupon she flew with it to her nesting site in the next tree, arranged this twig and quickly returned for another. As she tugged at a stubborn twig, her back was arched and her long tail curved under or waved about. If a twig resisted too well her attack, the bird desisted at once and tried another. Always she worked rapidly with great energy, attacking a twig as soon as she landed in the tree, never carrying more than one twig at a time, holding it squarely at right angles to her bill and flying rapidly with long tail streaming.

The Cuckoo's concentration in the work, coupled with her indifference to observers, was remarkable. Not once did she descend to the ground for material. Not once did she gather material in the tree in which her nest was located. With two exceptions the twigs were all gathered from the same tree. Working thus off and on for an hour or two at a time, the bird completed the nest. The third night the Cuckoo was sitting on the nest at dusk, but after two days she deserted.

Eggs.--The yellow-billed cuckoo lays ordinarily three or four eggs, sometimes only one and rarely five; as many as six, seven, or even eight eggs have been found in a nest, but these larger numbers may be the product of more than one female. The eggs vary in shape from elliptical-oval to oval, oftener nearer the former, and about equally rounded at both ends. The shell is smooth, but without gloss. Bendire (1895) says that the "color varies from a uniform Nile blue to pale greenish blue when fresh, fading out in time to a pale greenish yellow." Eggs that I have examined in collections vary in color from "pale glaucous green" to "pale flourite green."

The measurements of 53 eggs average 30.4 by 23 millimeters; the eggs showing the four extremes measure 34.64 by 23.11, 33.53 by 25.40, 27.43 by 22.86, and 29.21 by 20.83 millimeters.

Young.--The period of incubation is said to be about 14 days; it is shared to some extent by both sexes, but is probably performed mainly by the female. The eggs are sometimes laid on succeeding days, but oftener at more or less infrequent intervals, and young of different ages are often found in the nest.

Snyder and Logier (1931) say of a brood of young that they examined: "The young were quite active when disturbed. They scrambled about the bush, using the wings and bill for climbing. One young which was brought to our camp demonstrated a remarkable reptile-like behaviour. When it was placed on the table and one reached to pick it up, it erected its somewhat horny plumage and emitted a buzzing hiss like the sound of bees escaping from a tunnel of dry grass. This performance was certainly unbirdlike in all respects."

Francis H. Allen writes to me: "I found a young one in an open field on the ground. I was attracted to the spot by its loud rasping cry. It fluttered along when I approached, but it could not fly from that position, in rather long grass, though wings and tail were pretty well fledged. When I picked it up, it pecked my finger angrily. It seemed as fierce as a young hawk, and its rasping cry was probably calculated to inspire terror in its enemies. I placed the bird on a bough of a Norway spruce, where it took a characteristic cuckoo attitude and seemed much more at home than on the ground."

Dr. Lawrence H. Walkinshaw has sent me some notes on the weights and development of young yellow-billed cuckoos. One "well-grown" young was weighed for three days in succession before it left the nest, at 6 a.m. each morning. It weighed 28.8 grams the first morning, 31 grams the second, and only 26 grams on the third, August 6. The interesting point is that the loss of weight came with the sudden development of the plumage, of which he says: "When I visited the nest on August 5, at 6 a.m., his feathers resembled the quills of a porcupine, long and bluish, stretched out over his wings and back. At 7 p.m., these quills had all opened, and the bird had taken on the resemblance of an adult cuckoo. Correspondingly, the following morning, he had lost 5 grams in weight. He left the nest on August 6."

At another nest a young bird weighed 25 grams on August 25, 27.6 on the 26th, and 32.9 on the 27th, and only 28.9 grams on the 28th; this bird left the nest on August 29, with feathers unsheathed. He says that during the unsheathing process the young bird dressed its feathers continually; "the wings, the tail, the scapulars, the rump, and breast all shared alike, then with the feet he would work about the head and throat. When hungry he would pause and call a low cuk-cuk-cuk-cur-r-r-r-rrr. If the parent did not come soon, these calls increased in number. While feeding, his wings would vibrate rapidly, and after the parent left his call was more of contentment, a short curr, or a cuk-currrrr. When excreting, he simply backed up to the edge of the nest."

Plumages.--Bendire (1895) says: "The young when first hatched are repulsive, black, and greasy-looking creatures, nearly naked, and the sprouting quills only add to their general ugliness." This is a very good description, and the young birds do not improve much in appearance during the period of early growth. The body is well covered with the long, pointed feather sheaths until the young bird is more than half grown. But the sheaths burst, the juvenal plumage appears, and the young bird is well feathered before the time comes to leave the nest.

Dr. A. H. Cordier (1923) describes this process very well as follows:

At the end of seven days the young Cuckoo resembled a porcupine more than a bird. I now cut the limb holding the nest and brought it to the ground. Within three feet of it I then put up the umbrella tent that I might at close range observe minutely the rapid transition of the porcupine-looking object into a fully feathered, beautiful Rain Crow. . . .

The first picture was made at nine o'clock. . . . This shows the young by the unhatched egg; the horny, sheathed feathers were fully two inches long, making the bird look like a porcupine. About ten-thirty the sheaths began to burst, and with each split a fully formed feather was liberated. This process took place with such rapidity that it reminded me of the commotion in a corn popper or a rapidly blooming flower. All the while I was within three feet of the bird, and could see every new feather, as it blossomed, so to speak.

At three p.m., six hours after the first picture was taken, I made another photograph, showing this same bird in the full plumage of a Cuckoo, except the long tail.

In this first plumage the young cuckoo looks very much like the adult, perhaps slightly paler above and with a slight wash of tawny or pale buff on the throat and breast; but the tail is quite different, lacking the conspicuous black and white marking so prominent on the sides of the adult tail; in the young bird the dark spaces in the tail are not black, but dark gray or lighter gray, variable in different individuals or in different feathers in the same individual; the light spaces are not so sharply defined as in the adult and are grayish white instead of pure white.

The juvenal body plumage appears to be molted in fall, from August to October; but the juvenal wings and tail are worn through the first winter at least; I have not been able to detect this plumage in spring birds, so I suppose that a more or less complete molt occurs while the birds are in their winter homes, producing a practically adult plumage before they return in the spring. Adults have a complete molt between July and October, and possibly a more or less complete molt in spring before they arrive here, but winter specimens to show it are lacking.

Food.--Cuckoos are among the most useful of our birds, mainly because of their fondness for caterpillars, which are some of our most injurious insect pests and which constitute the principal food of these birds during their seasons of abundance. Edward H. Forbush (1907) writes:

The Cuckoos are of greatest service to the farmer, by reason of their well-known fondness for caterpillars, particularly the hairy species. No caterpillars are safe from the Cuckoo. It does not matter how hairy or spiny they are, or how well they may be protected by webs. Often the stomach of the Cuckoo will be found lined with a felted mass of caterpillar hairs, and sometimes its intestines are pierced by the spines of the noxious caterpillars that it has swallowed. Wherever caterpillar outbreaks occur we hear the calls of the Cuckoos. There they stay; there they bring their newly fledged young; and the number of caterpillars they eat is incredible. Professor Beal states that two thousand, seven hundred and seventy-one caterpillars were found in the stomachs of one hundred and twenty-one Cuckoos--an average of more than twenty-one each. Dr. Otto Lugger found several hundred small hairy caterpillars in the stomach of a single bird. The poisonous, spined caterpillars of the Io moth, the almost equally disagreeable caterpillars of the brown-tail moth, and the spiny elm caterpillar, are eaten with avidity.

He says elsewhere (1927):

When, in time, the inside of the bird's stomach becomes so felted with a mass of hairs and spines that it obstructs digestion, the bird can shed the entire stomach-lining, meanwhile growing a new one. . . . Mr. Mosher, a competent observer, watched a Yellow-billed Cuckoo eat 41 gypsy caterpillars in fifteen minutes, and later he saw another consume 47 forest tent caterpillars in six minutes. . . . Dr. Amos W. Butler [1897] says that he has known these Cuckoos to destroy every tent caterpillar in a badly infested orchard and tear up all the nests in half a day. This species frequently feeds on or near the ground, and there gets an enormous number of locusts and other pests. In summer and autumn it feeds to some extent on small wild fruits, such as the raspberry, blackberry and wild grape.

The fall web worm is a destructive pest on certain trees, but few birds will eat it. Dr. Sylvester D. Judd (1902) noted that, on a Maryland farm, "a pair of yellow-billed cuckoos continually extracted them from the webs. The destruction of this insect is an habitual practice with the cuckoo. In a single stomach of the species examined by Professor Beal there were 325 of the larvae."

Henry C. Denslow writes to me that he fed many hairy caterpillars to a cuckoo that he had in captivity, and says: "Many of these this bird sheared the hairs from by slowly moving them from end to end through its beak by a side-shifting motion of the mandibles. The removed hairs collected in a little bunch and, at the end of the caterpillar, fell to the floor. Most of the hairs were thus shorn from these caterpillars. Other caterpillars were swallowed entire, as I gave them to him, hairs and all."

Walter B. Barrows (1912) says that this cuckoo feeds freely on elderberries and mulberries and that "large quantities of beetles and bugs also are consumed, and both species of cuckoo seem to be very fond of grasshoppers, eating especially such forms as frequent shrubbery and trees, among these the destructive tree crickets (Oecanthus). Ten specimens examined by Professor Aughey, in Nebraska, contained 416 locusts and grasshoppers, and 152 other insects."

Audubon (1842) writes:  "In autumn they eat many grapes, and I have seen them supporting themselves by momentary motions of their wings opposite a bunch, as if selecting the ripest, when they would seize it and return to a branch, repeating their visits in this manner until satiated."

In addition to those mentioned above, yellow-billed cuckoos have been known to eat many other insects, such as army worms, ants, wasps, flies, and dragonflies. Several of the earlier ornithologists accused this cuckoo of eating the eggs of other small birds and produced some evidence of the bad habit, but some modern observers seem to think that they do very little, if any, nest robbing. C. J. Maynard (1896) writes:

This species in company with the former [black-billed cuckoo] are the terror of other small birds during the nesting season for they will constantly rob their nests. I have frequently seen a Cuckoo enter a thicket in which a Robin or a Cat Bird had built a home and in a moment the air would resound with the shrill cries of distress given by the parents, causing all the small birds in the immediate vicinity to rush to the spot and as each joins in the outcry, the noise produced is apparently enough to frighten away a bolder bird than a Cuckoo.

But in spite of all this din, the glossy thief nearly always succeeds in accomplishing his purpose and emerges from the thicket, carrying an egg impaled on his beak. He does not always escape unscathed, however, for he is pursued by a motley crowd consisting of Robins, Cat Birds, Thrushes, Warblers, etc. that follow him closely, harassing him on all sides, and some of the more courageous will even assault him with blows from their beaks so that he frequently leaves some of his feathers floating in the wind behind him. As the long and broad tail of the Cuckoo is a prominent object and as it is also a portion of the bird which its enemies can seize with comparative safety to themselves, this member often suffers in these forays, in so much, that by the middle of summer, it is quite difficult to find a Cuckoo of either species which has a full complement of tail feathers.

On the other hand, Major Bendire (1895) says: "I am aware that this species has been accused of destroying the eggs and even of eating the young of smaller birds, but I am strongly inclined to believe that is accusation is unjust, and in my opinion requires more substantial confirmation. I have never yet had any reason to suspect their robbing smaller birds' nests, and the very fact that they live in apparent harmony with such neighbors, who do not protest against their presence, as they are in the habit of doing should a Blue Jay, Grackle, or Crow come too close to their nests, seems to confirm this view."

But then he goes on to quote from a letter from William Brewster, who says:  "While I have never seen either of our Cuckoos destroy the eggs of other birds, nevertheless, I think they do it occasionally. One of my reasons for this belief is that many of our small birds, Warblers, Sparrows, etc., show great anxiety whenever the Cuckoos approach their nests, and they pursue and peck at them when they take wing, behaving toward them, in fact, exactly as they do toward the Crows, Jays, and Grackles, which we know eat eggs whenever they can get a chance. My other reason is that one of my friends once shot a Cuckoo (C. americanus, I think it was) whose bill was smeared all over with the fresh yolk of an egg."

Yellow-billed cuckoos sometimes eat tree frogs and other small frogs, and, in the Southern States, an occasional small lizard. Marcia B. Clay (1929) relates the following incident: "For an hour a Cuckoo searched about the dead under limbs of a huge untrimmed apple tree, peering and gliding noiselessly around and around. At last, after long and patient search, it dashed to the ground and began to walk directly toward me through the scant grass and weeds, and only then did I see a frog trying to slip away unseen. The bird followed the frog a rod, pecking its victim and gloating softly Cuk, Cuk. Having vanquished its prey, the Cuckoo deftly gathered it into its bill and flew away, the frog's legs sticking out out stiff and straight together, exactly like the dead twigs which the Cuckoo carries to its nest."

Behavior.--Mr. Forbush (1927) has described the quiet, retiring behavior of the yellow-billed cuckoo very well as follows:

The cuckoo is a graceful, elegant bird, calm and unperturbed; it slips quietly and rather furtively through its favorite tangles and flies easily from tree to tree in the orchard, keeping for the most part under protection of the leaves , which furnish excellent cover for its bronzy, upper plumage, while the shadows of the foliage tend to conceal the whiteness of its under parts. It has a way also of keeping its back with its greenish satiny reflections toward the intruder in its solitudes, and while holding an attitude of readiness for flight it sits motionless, and its plumage so blends with its leafy environment that it does not ordinarily catch the eye. In the meantime it turns its head and regards the disturber with a cool, reserved, direct gaze, looking back over its shoulder, apparently unafraid and giving no indication of nervousness or even undue curiosity; but if the observer approaches too closely, the elegant bird slips quietly away, vanishing into some leafy, cool retreat where it may enjoy the silence and solitude, dear to the woodland recluse.

The flight of the cuckoo is rather swift, easy and graceful, exceedingly direct and horizontal, but turning frequently from side to side as it threads its way through the branches of the trees, giving occasional glimpses of its white under parts and the telltale black-and-white markings in its tail; it is stream-lined to perfection and glides noiselessly through the air with its long tail streaming out behind. It is very quiet in its movements in its shady retreats; it seldom perches in a conspicuous place but sits motionless for long periods in the dense foliage, watching, or moves about stealthily in search of its prey. It might easily be overlooked, were it not for its characteristic notes, which lead the observer to look for it.

About its nest it is rather shy, while incubating on its eggs, slipping away cautiously when approached, but when there are young in the nest its behavior is quite different. It then becomes quite solicitous and will often remain on the nest until almost touched, and then perhaps throw itself down to the ground, fluttering and tumbling along, feigning lameness, after the manner of many ground-nesting birds, uttering loud, guttural cries of distress.

Voice.--We hear the voice of the cuckoo much oftener than we see the bird; the well-known sound comes to us, like a wandering voice, from the depths of some shady retreat, but we cannot see the hidden author. We can recognize it easily as the voice of a cuckoo, but it is not always so easy to identify the species by its notes, though some keen observers claim that they can do so. Certain songs are characteristic of each of the two species, but both have a great variety of notes and many notes that are much alike in both. The notes of the yellow-billed cuckoo may be a trifle harsher and a little louder, but they are not always recognizable. The characteristic note of the yellow-billed cuckoo is well described by Charles J. Spiker (1935) as follows: "What may be considered the song of this species is a series of rapid, wooden-sounding syllables resembling the following: Kuk-kuk-kuk-kuk-kuk-ceaow-ceaow-ceaow-ceaow; the kuks being given rapidly, and the ceaows more deliberately and with longer intervals."

Bendire (1895) writes:

One of their commonest notes is a low "noo-coo-coo-coo"; another sounds more like "cow-cow-cow" or "kow-kow-kow," several times repeated; others resemble the syllables of "ough, ough, ough," slowly uttered; some remind me of the "kloop-kloop" of the Bittern; occasionally a note something like the "kiuh-kiuh-kiuh" of the Flicker is also uttered; a low sharp "tou-wity-whit" and "hweet hwee" is also heard during the nesting season. Though ordinarily not what might be called a social bird, I have sometimes during the mating season seen as many as eight in the same tree, and on such occasions they indulge in quite a number of calls, and if the listener can only keep still long enough he has an excellent opportunity to hear a regular Cuckoo concert.

Various other interpretations of the different notes have been given by other writers, but the above quotations cover fairly well the ordinary variations. The song, as given by Mr. Spiker above, is sometimes more prolonged by lengthening the series of kuks, with increasing speed of utterance and adding to the series of ceaows, with slowly decreasing speed. I believe that the black-billed cuckoo never gives this prolonged song, accelerated during the fist half and retarded during the last half; its song is given in more even time, and is generally shorter. The song of the yellow-billed cuckoo is often heard during the night, and its notes are often uttered while flying.

Field marks.--A cuckoo may be easily recognized as a cuckoo by its size, shape, and color--a long, slender bird, longer than a robin, with a long tail, olive-brown above and white below; but the two species look very much alike unless the distinctive markings can be clearly seen. The yellow lower mandible of this species can be seen only at short range. But the rufous in the wing feathers is evident in flight, and the lateral tail feathers are conspicuously black, with large terminal white areas clearly defined. At very close range, the yellow eyelids of this species may be seen.