Cooper's Hawk | Life Histories of North American Birds | A.C. Bent
Feather Pic Arthur Cleveland Bent

Life Histories of Familiar North American Birds
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Cooper's Hawk
Accipiter cooperii

[Published in 1937: Smithsonian Institution United States National Museum Bulletin 167: 112-125]

If the sharp-shinned hawk is a blood-thirsty villain, this larger edition of feathered ferocity is a worse villain, for its greater size and strength enable it to do more damage. Furthermore, it is much more widely common during the breeding season, being one of our commonest hawks in nearly all parts of the United States. It is essentially the chicken hawk, so cordially hated by poultry farmers, and is the principal cause of the widespread antipathy toward hawks in general.

In my early bird-nesting days, 30 and 40 years ago, this was one of our commonest nesting hawks; but for the past 30 years it has been steadily decreasing in numbers. This is perhaps due to constant persecution, but it is largely due also to the marked decrease in the numbers of small birds. I have always considered this and the sharp-shinned hawk as competitive species, each intolerant of the other. I have frequently found one of these Accipiters nesting in the same tract of woods with one of the Buteos, but I have never found the two species of Accipiter nesting in the same tract; and several times I have known cooperi to replace velox in a tract where the latter had repeatedly nested. It is a curious fact that the solitary vireo (Lanivereo solitarius) has so often been found nesting in pine woods occupied by a pair of Cooper's hawks as to suggest some significance in the ecology; I find six such cases recorded in my notes, and once the vireo's nest was within 50 feet of the hawk's nest; we have also noted that we never find the vireo in similar woods occupied by sharpshins; the reason seems obvious.

Nesting.--Cooper's hawk is still a fairly common breeder in southeastern Massachusetts, though my records show that we found three times as many nests during the 20 years previous to 1910 as we have since then. My earliest date for a full set of eggs is April 22, and my latest date for heavily incubated eggs of the first laying is June 3. But I have only six records for April and only three for June, leaving 39 records for the month of May. According to our experience here, Cooper's hawk shows a decided preference for white-pine groves as nesting sites; but it is not nearly so closely confined to this type of woods as is the sharp-shinned hawk. Our notes record 27 nests in white-pine woods, 16 in deciduous woods, mostly oaks and chestnuts, 4 in mixed woods, oaks, chestnuts, and pine, and 1 in a pine on an open knoll among a few scattered oaks; this last was occupied by a pair that had nested the previous year in a tract of oak woods nearby that had since been cut off. Of these 48 nests, 29 were in white pines (Pinus strobus), 11 were in oaks (red, scarlet, and swamp white), 6 were in chestnuts, and 3 in maples. The heights from the ground varied from 20 to 60 feet,  but approximately half of them ranged between 35 and 45 feet. I believe that the Cooper's hawk prefers to, and generally does, build a new nest each year, but the old nest is sometimes repaired and sometimes a nest is built on an old squirrel's or crow's nest. A new nest is a clean, substantial structure of sticks and twigs, varying in shape and dimensions according to its location. Nests in white pines are rather broad and flat, built on two or three horizontal branches and against the trunk. A typical new nest of this type will measure about 28 by 24 inches in length and breadth and 7 or 8 inches in height. In one case, where a new nest had been built on top of an old one, the combined structure was 27 inches high. Nests in deciduous trees are usually built in upright crotches, and are higher but not so broad. An extreme nest of this type, built in the 4-prong main crotch of a chestnut, measured 18 inches in diameter and 30 inches in height; it was probably built on an old nest of some sort. The inner cavity is usually about 7 inches wide and 2 to 4 inches deep, depending on the condition of the outer rim. The inner cavity is always, according to my experience, lined with chips, or flakes, of the outer bark of pines or oaks; I have never seen a nest containing a full set that lacked this bark; but I believe it is usually added after some, or all, of the eggs are laid. Occasionally a few sprigs of green pine needles are added, and once I found a nest that was profusely lined with this material, together with the usual bark flakes.

A Cooper's hawk's nest can usually be recognized by its size, shape, and location. Bits of down are oftener seen on this than on the sharpshin's nest, but it is never so heavily decorated with down as a Buteo's. Often the long tail of the incubating bird may be seen projecting over the edge of the nest. Usually the bird darts away with great speed and is not seen again; sometimes one or both birds fly about and cackle; but I have never found them so bold and aggressive as sharpshins. Often the location of a nest is betrayed by the cackling. Generally one finds in the nesting woods the feathers of ruffed grouse, poultry, or smaller birds. Sometimes these hawks use an old nest as a feeding station; these nests are well decorated with feathers of the hawks and their victims. In one such nest I once found the feathers of a screech owl. Cooper's hawks often return to the same patch of woods to nest for several years in succession, but we have never found them so constant in their attachment to a locality as the red-shouldered hawk.

Bendire (1892) says: "On the plains where, from scarcity of suitable timber elsewhere, they are confined to the shrubbery of the creek bottoms, consisting mainly of cottonwoods and willows, they sometimes nest as low as 10 feet from the ground, and I have here found some of their nests fairly well lined with the dry inner bark of the cottonwood and with weed stalks; while in the vicinity of Grand Forks, North Dakota, according to information furnished me by Mr. G. G. Cantwell, they are said to nest occasionally directly on the ground."

He quotes from Denis Gale, regarding a peculiar Colorado nest, as follows: "On June 25 I found a nest of a Cooper's hawk containing four unmarked bluish white eggs, resting upon some thin flakes or scales of spruce bark, which alone constituted the lining of the nest, the available contrivance for which was a large bunch of matted scrub, and excrescence upon a horizontal limb, about 18 inches from the trunk and about 20 feet from the ground. This bunch consisted of a wonderful growth of very densely interlaced twigs, the surface of which offered a commodious nesting site, having not only an ample flat area, but a sufficient depression in its center to meet every requirement for a nest."

In Arizona we found several nests of Cooper's hawks generally high up in the tops of the giant cottonwoods or sycamores in the mountain canyons; only one was climbed to, as it was only 40 feet up in a blackjack oak. In Texas these hawks nest in the lofty tops of the heavily timbered deciduous forests in the river bottoms.

John H. Flanagan (1901), in Rhode Island, robbed a red-shouldered hawk's nest on April 20 and found a Cooper's hawk's nest within 20 feet of it; 10 days later he took the eggs of the latter also; and on May 12 he was surprised to see the Cooper's hawk fly from the redshoulder's nest, in which it had already laid three eggs. A climb to the nest showed that every vestige of the inner bark (which the redshoulder always uses) had been removed. A few small sticks had been added and the nest relined with outer bark.

Clarence F. Stone (1899) had an unusual opportunity to watch a pair of Cooper's hawks building their nest, which he describes as follows:

I spied the half completed nest just as one of the hawks left it and thought I had been discovered, but an instant later the mate lit upon the nest and arranged a stick.

Their manner of approaching the nest was a very interesting and curious sight. They came through the low woods flying just above the ground three or four feet, with the speed of an arrow, and when within fifteen or twenty feet of the nest-tree they closed their wings with a quick flip and "slid up" to the nest in a graceful curve.

They did not visit the nest together and apparently the one that was away from the nest could see its mate, for no sooner would one of them drop a few feet below and fly away, than the other was on the upward curve. As if to avoid collision they left the nest from the north side and approached from the west, in which direction--and only a few rods away--all the material seemed to be obtained.

While at the nest their actions were quick, nervous; and they placed the sticks in several places before satisfied, but they did not remain at the nest more than half a minute.

If a set of eggs is taken from a nest the hawk will lay a second set, about ten days or two weeks later, sometimes in the same nest, but oftener in another nest hastily repaired. C. J. Pennock tells me that, after taking four eggs from a nest on April 26, he took two more on May 5 and two additional eggs on May 11, all from the same nest.

If either one of a pair is shot during the nesting season, the survivor usually secures a new mate quite promptly. J. Eugene Law (1919) mentions the following incident, related by Maj. Allan Brooks: "A female Cooper Hawk had been shot from her nest of eggs. Some days later another female, in adult plumage, was found incubating the same eggs, and was likewise shot. What was his surprise later was to find a third female occupying the nest, this time a bird in the streaked plumage of a sub-adult. And as a matter of curiosity she was allowed to, and did, raise the brood."

Eggs.--Four or five eggs form the usual set for Cooper's hawk; sometimes only three are laid; I have taken one set of six and heard of two or three others. Just half of the sets recorded in my notes have been of four, and one-quarter of them of five. They are deposited at intervals of one or two days. The eggs are rounded-ovate to ovate in shape, and the shell is smooth but not glossy. The color, when fresh, is bluish white or greenish white, which fades out to dirty white. They are generally nest stained but otherwise immaculate and not attractive in appearance. From 25 to 50 percent of the eggs show more or less scattered spotting in pale browns or buffs; rarely some of them are as heavily marked as some of the paler types of red-shouldered hawks' eggs. Major Bendire (1892) says: "Mr. C. J. Pennock has a set of five eggs in his collection, in which the ground color is a rich bright green, and four of these eggs are distinctly and handsomely marked. They were collected by himself near Kennett Square, Pennsylvania, May 2, 1887."

The measurements of 62 eggs average 49 by 38.5 millimeters; the eggs showing the four extremities measured 54 by 40, 51.5 by 42, and 43 by 34 millimeters.

Young.--Incubation is shared by both sexes, does not usually begin until all, or nearly all, the eggs are laid, and is said to last for 24 days. The young hatch at intervals of one or two days, perhaps less, for there is very little difference in size noticeable among small young. A brood that I watched and photographed were still in the eggs on June 4; on June 18, when probably 10 to 12 days old, their plumage had not started to grow, but they were very bright, active, and playful; only two of the four eggs had hatched; one egg was evidently addled and buried in the lining of the nest, but the other had disappeared. On June 30 they were about two-thirds grown and partly feathered; one, probably the female, was considerably larger than the other. I made my last visit on July 11, when one of the young had disappeared and the other was perched on a limb above the nest. I climbed the tree with my camera, but before I got within range, he climbed out to the end of the limb and then flew clumsily over to the next tree; he repeated the operation when I climbed to the next tree and I saw him fly from tree to tree with increasing confidence, until I gave up the chase. His wings and tail were nearly grown, but he was still partially downy; he was then about five weeks old. I had noticed on previous visits that while there were only eggs in the nest it was lined with the usual flakes of outer bark; but after the young had hatched it was relined with fresh green sprigs of pine; this lining, however, was not renewed after the young were half grown.

My attempts to rear young Cooper's hawks in captivity have not succeeded; they have always been wild and untamable. But Dr. H. Justin Roddy (1888) has been more successful; he writes of one he took from a nest when not more than two weeks old:

It was a great eater. When six weeks old it ate nine English Sparrows (Passer domesticus) and a common mouse (Mus musculus) in one day; and ate on an average eight Sparrows a day from that time until it was ten weeks old. . . . In eating the bird tore its food to pieces with the bill, nearly always beginning at the entrails. It almost always seemed to relish the intestines more than any other part of the bird or animal, sometimes eating only this part and leaving the rest. When the bird or animal was still warm and the blood therefore uncoagulated, it tore it open and apparently bathed the bill in the blood and the visceral juices. It apparently sucked up these fluids in order to allay thirst. But I invariably found it refused water--in this respect acting quite differently from the Cathartes aura, which drank water freely. . . .

The bird became very much attached to me, and even when it could fly and was allowed its liberty did not leave, but returned every few hours for its food, which I always liberally provided. How long it would have continued to do this I do not know, as the experiment ended with its death. It was shot by one who did not know it was my pet.

William Brewster (1925) writes:

While skirting the edge of a deep and heavily-wooded glen on the north side of Upton Hill, half a mile or more from the Lake, I heard on August 4, 1874, a succession of shrill, squealing whistles repeated at frequent intervals. Cautiously approaching the place whence these sounds came, I presently discovered four young Cooper's Hawks not quite fully grown or feathered, and still tufted here and there with fluffy, whitish down, standing close together in a row on a prostrate log. Every now and then one would unfold and raise its wings, flapping them to preserve its balance, as it took a few unsteady steps along the log, at the same time uttering the whistling cries above mentioned. One and all stood very erect when not in motion, and young as they were lacked little if anything of that stern and dignified bearing so characteristic of adult Hawks at most, although by no means all, times. After watching them awhile I shot one, when the three survivors flew heavily up into a spruce where another was promptly killed, the remaining two being permitted to escape.

Plumages.--In the first downy stage the young Cooper's hawk is thickly covered above, and more thinly below, with short white down, faintly tinged with cream color above. This short down is replaced later, before the plumage starts to grow, with long, woolly, pure-white down, with which the young bird is thickly covered above and below. The juvenal plumage starts to grow before the bird is three weeks old, beginning on the wings and tail, closely followed by the scapulars, back, and sides of the breast. Two young birds, about 22 to 24 days old, had the remiges about one-third grown and the rectrices less than one-quarter grown, all partly in sheaths. The young leave the nest when about five weeks old, before the flight feathers are fully developed and while still partially downy on the head, center of the breast, flanks, and legs.

In fresh juvenal plumage the upper parts are "bone brown" to "clove brown," edged on the crown and tipped on the back, wing coverts, and upper tail coverts with "tawny" or "ochraceous-tawny," lightest on the tail coverts; there is a white line over the eye; the chest is washed in "pinkish cinnamon" and heavily marked with broad, hastate, dusky streaks; the flanks and breast are white, with narrow dusky streaks; the belly is immaculate white; and the legs (tibiae) are marked with "buffy brown" cordate spots. This plumage is worn throughout the first winter and spring, the colors fading somewhat and the edgings wearing away. Young birds begin to breed in this plumage. A complete molt begins in June, starting with the wings and tail and ending with the body molt in summer. This produces a second-year plumage that is practically adult, but the full perfection of the adult plumage is not acquired for at least another year.

Adults have a complete annual molt from July to October. The sexes are alike in juvenal plumage; the adult male is more brightly and heavily marked below and more bluish above, the female being duller below and more brownish above. The female is much larger in all plumages.

Food.--Cooper's hawk does more damage in the poultry yard than all other hawks put together. It is very destructive to domestic pigeons, of which it is very fond, and if not killed, will soon clean out a colony. It soon learns also where it can find an convenient supply of half-grown chickens or young ducks, to which it makes frequent visits, until its career is ended. It is not easily killed, however, as it is usually crafty enough and quick enough to avoid the farmer's gun. Dr. A. K. Fisher (1893) says: "Dr. William C. Avery, of Greensboro, Ala., informs us that during one year he killed and wounded at least a dozen of these Hawks before the inroads among his doves ceased. . . . Dr. Warren states that a pair of these Hawks destroyed some fifty chickens from one farm, twelve of which were taken in a single day." He summarizes the food of this hawk as follows: "Of 133 stomachs examined, 34 contained poultry or game birds; 52, other birds; 11, mammals; 1, frog; 3, lizards; 2, insects; and 39 were empty."

Among the wild birds mentioned in the food of Cooper's hawk are teal and young of other ducks, least bittern, snipe, screech owl, quails, partridges, grouse, doves, small hawks, flickers, blackbirds, jays, meadowlarks, woodpeckers, grackles, numerous sparrows, towhees, a few warblers, vireos, nuthatches, thrashers, catbird, robin, and thrushes. The list of mammals includes hares, rabbits, opossum, various squirrels, skunks, rats, and mice. It sometimes eats snakes, lizards, frogs, grasshoppers, crickets, beetles, and even butterflies and moths. Austin Paul Smith (1915) says that during a drought in Arkansas, when most of the streams were dried up, he "flushed, on several occasions, this hawk in the act of feeding upon minnows in the desiccating pools."

Behavior.--The flight of Cooper's hawk is very similar to that of the sharp-shinned hawk, a low, swift, dashing flight. It surprises its prey by a sudden, swift dash, pouncing upon it before it has a chance to escape. Its short wings and long tail give it such control of its movements that it can dart in and out among the branches of the forest trees with impunity, or dodge through the intricacies of thickets where its victims are hiding. Dr. Daniel S. Gage has sent me some notes illustrating its crafty methods of approach. He was watching a robin at the base of a tree in some thick woods when he saw a hawk come, flying swiftly and keeping the trunk of the tree between him and the robin; when close to the tree the hawk swerved around it and barely missed catching the robin. Again he saw a hawk approach a field of tall weeds, in which some small birds were feeding, flying close to the ground behind a fence, dash over the fence, and pounce on one of the birds. On another occasion, a hawk had seen, while perched on a distant tree, some chickens in a yard close to a house; he flew low, behind the house until close to it, rose over the house and pounced down on one of the chickens, which had no chance to escape until he was right upon them.

M. P. Skinner relates the following incident in his Yellowstone notes:

As I rode up the loop road through the aspens above Mammoth, I heard quick, frightened bird cries on either side, and I even seemed to sense the excitement in the air. I turned about to see what was happening and a Cooper hawk came shooting up the road past me, four feet above the road and going at great velocity. A Kennicott ground squirrel that no doubt had been attracted to the road by spilled oats, tried to cross the road only to be struck amid a cloud of dust. After striking the squirrel the hawk went on for six feet more before it could turn. Meanwhile the squirrel was stretched out in the road lifeless. The hawk came back and attempted to carry off its booty. But I dashed up at a gallop, and as the prey was too heavy to carry off quickly, the hawk had to drop it. I picked it up and found that only one claw had pierced the skin, and only a drop or two of blood had come out. So I believe that the squirrel was killed by the force of the blow itself.

The following remarkable performance is described by William Savage (1900):

I was standing in a thick brush at the time, when suddenly I heard a loud rushing of wings, rather behind me, and, on looking around, saw a quail flying past at its utmost powers of flight and about twenty feet behind was a Cooper's Hawk, but pursuing with such rapidity that I could plainly see it was gaining on the quail. I discovered in a moment that the quail was endeavoring to reach a clump of hazel bushes nearby, though apparently intending to pass them, but when about six feet above and directly over the desired covert, it suddenly dropped like a dead bird for the refuge. The hawk, however, was not to be eluded by this bit of strategy, for with an extra effort, it shot beneath its prey, at the same time turning with its back next to the ground and spreading its murderous claws wide open, the quail actually falling into them; then righting up, sailed away with its prize. This I think was done in about ten seconds.

But the hawk is not always successful in capturing its prey; sometimes it meets more than its match; and sometimes it may attack for the mere sport of it. At least two observers have noted its fruitless attempts to capture a kingfisher in flight over water. As the hawk gained on the slower bird, the latter, at the most critical moment, suddenly dove into the water and the hawk's momentum carried it far beyond. As the kingfisher rose the hawk returned to the attack, with the same result, which was repeated six or eight times. After the last fruitless attempt the hawk gave it up; the kingfisher, as Charles E. Johnson (1925) says, "alighting on a perch at the water's edge, with bristling crest and many a hitch and jerk, as if to reassure itself of its own personal solidarity, burst forth in a rattle, loud and ringing with triumph if not actually vibrant with inexpressible scorn."

Charles W. Michael (1921) relates the following incident:

Looking up we saw the two rather large birds dashing through the treetops. The dark bird with the white wing patches we recognized at once as a Pileated [woodpecker]; the lighter colored bird turned out to be a Cooper Hawk. A pursuit was apparently in progress, but as the birds dashed through the branches of the tall trees it was impossible to be sure which of the birds was the pursuer and which the pursued. Both birds quickly left our range of vision, but a little farther on we heard gentle tappings and soon located the woodpecker. The hawk was there too, perched on a limb a few feet away. The woodpecker was drilling and prying off chips with apparent unconcern, while the hawk looked on with seemingly hungry eyes. While we were watching, the hawk flew to a branch a few feet above the woodpecker. Pileated tilted his head and gave the hawk a sidelong glance and then deliberately flew toward him and drove him from the tree. With the hawk gone, the woodpecker went on with his drilling as though nothing had happened.

Lewis O. Shelley has sent me the following note:

In May 1929, while I was watching a wave of migrating warblers from the partly sheltered location beneath an old-growth white pine, in a wood not more than a hundred yards wide, my attention was called to a Cooper's hawk erratically flapping back and forth overhead, diving now and then at something I could not see and accompanying each dive and rise with its screamed cry. Finally I detected a flicker dodging among the pines in what seemed to me perfect safety if it had only alighted instead of dodging. But it was bewildered for it continued flying from one side to the other of the woods, the hawk following each movement just under the treetops. Then, when the flicker made a headlong flight toward the open and a scrub apple tree, the hawk gained speed and lunged, checking its speed with spread wings and spread tail thrown downward and forward as it struck its prey, turned, and carried its booty in under a pine, commencing to pluck the feathers before the flicker's cries had died out. I examined the remains of the feast and found only the bill and a carpet of feathers!

Crows often attack Cooper's hawks, as they do owls, sometimes singly, but more often in mobs, chasing the hawk about until it is forced to seek refuge in the woods. Sometimes the tables are turned and the hawk chases the crows, though I doubt if this often results fatally for the crow. Joseph Mailliard (1908) once saw a pair of these hawks attacking a flock of crows. The crows were quietly perched in some dead trees. "One hawk would perch on top of a tree above the crows, while the other would go off a little way and then swoop down on the flock, repeating the operation with variations."

H. W. Henshaw (1875) writes:

While sitting in my tent one day at Camp Apache, I noticed one of these hawks making repeated attacks upon a raven. It would force the raven to take refuge in a tree, and then fly to some neighboring perch and take its stand. The moment the persecuted raven essayed to move away, the hawk flew out and swooping down upon it stuck it and again forced it to cover. This was repeated several times and apparently for no other reason than for the amusement of the hawk; though, judging from the discontented squawks and cries which the abused raven gave vent to, the pleasure was by no means mutual. So engrossed was the falcon in this sport that it allowed me unnoticed to walk up within a few feet, when my gun settled the dispute.

About its nest Cooper's hawk is usually shy, flying swiftly away and generally not returning to protest, although it sometimes flies about cackling. When there are young in the nest it is much bolder; I have had one dash at me while I was near the nest tree or alight in the tree near me while I was at the nest. I once saw one attack a great horned owl that came too near its nest.

The following account by Dr. Paul L. Errington (1932) illustrates the ferocity and bravery of a Cooper's hawk in defense of its young:

On July 7, 1931, I was visiting a juvenile Great Horned Owl that had previously been tethered on the ground for a study of its food habits in a woodlot west of Pine Bluff, Wisconsin. The adult owl that was taking care of the youngster appeared at my approach, alighted in a tree near by, and started the usual hostile demonstration of hooting and bill snapping. As if in answer to the hoots, the cry of a Cooper's Hawk came from deeper in the woods, and an instant later a female hawk dashed at the adult owl with terrific speed. Like a skilled boxer, the owl ducked, barely evading the hawk's talons. Several times in very short order the owl had to dodge as the raging hawk struck from all sides.

During the first part of this performance, the owl had been nearly as much concerned on account of my proximity to the juvenile as it had been with the attacks of the Cooper's Hawk. Finally, things became sufficiently hot that the owl left the branch upon which it had perched, and launched forth in direct and purposeful chase of the Cooper's Hawk, which kept just ahead of her larger pursuer for several yards before doubling back, to wheel and strike again. The hawk behaved as though utterly maddened, but she never let herself get quite within reach of the owl's talons. Her safety was plainly dependent upon her superior agility and precision of movement. For a brief space the action became so fast that I could not see exactly what was happening, especially at close quarters when it seemed that neither bird could avoid being hit. However, it is improbable that damage was done, for not even a feather was noted to fall. The hawk soon went her way, cackling as she flew, and the owl was free once more to center upon me its earnest attention. The hawk gave no evidence of having seen me.

A search of a few minutes revealed the hawk's nest 110 yards away. Two juveniles, ready to fly, were perched on the rim.

Many demonstrations of its impudent boldness in pursuit of its quarry have been recorded. Dr. Charles W. Townsend (1930) says: "The Cooper's Hawk, like the Sharp-shin, is bold in the presence of man. I have known one, in pursuit of a chicken, to fly into a barn where it was killed with a whip by a farmer. Another had trussed and nearly eaten a Robin on the ground near my house and did not fly until I had approached within ten feet."

Dr. Fisher (1893) tells of one of these hawks that attacked Dr. C. D. Walcott, while he was collecting fossils, apparently with no provocation; the hawk was repelled but renewed the attack and was killed with a geological hammer. Mr. Forbush (1927) quotes Mr. Farley, as follows:

This Sunday morning, May 2, 1909, soon after 9 (apparently his usual hour), the Cooper's Hawk (or another just as bad) which is getting so many chickens from poultry-raisers here on Chiltonville Hill, Plymouth (we have lost 25), appeared, coming for the coops. Mr. Graves fired at him, but the hawk, not stopped by the report, circled within a few rods and came in again. But the second barrel sent him away, apparently hit. During this entire episode there were five people standing close to the coop. A few mornings ago also, as Mr. Graves was pounding away making another coop, the hawk caught and carried off a chicken within a few yards of him. A Cooper's Hawk two years ago in East Bridgewater behaved similarly. Four times this daring bird (with people standing near) tried to get a chicken out of a hen-yard that adjoined the mixed woods where it had its nest. The people "shooed" the hawk away three times, but at the fourth attempt, despite their cries, it carried off a pullet.

Enemies.--The Cooper's hawk has few enemies, except for the farmer or the sportsman with a gun, but the following account, sent to me by Clyde L. Field, shows that the spunky little kingbird can make life miserable for this hawk and defend its territory successfully against it:

Once while traveling along some foothills in Arizona, where bird life was very scarce, I came to a small grove of sycamores. Here birds were very abundant. Nesting had not yet started, except for a pair of Cooper's hawks. On account of these hawks, I little hoped that many of these birds would live through the summer, but, much to my surprise a month later, they were still there and as many as before.

The answer was soon forthcoming, for up the creek came a badly scared Cooper's hawk with a flock of kingbirds in hot pursuit. The kingbirds were striking at him from all angles and, at each hit scored, the hawk would let out a squawk. This was repeated several times during the day.

I came upon one of the hawks sitting on a limb with two kingbirds diving at it. One of the kingbirds struck him, causing him to lose his balance. Taking advantage of this, the other kingbird hit him again, knocking him off. Down the creek they went, with more kingbirds joining the chase. The kingbirds made living possible here for the other small birds in the grove.

Voice.--The ordinary alarm note, heard about its nest, is a loud, metallic, cackling note, similar in form to the corresponding note of the sharp-shinned hawk, but louder and on a lower key. I have always written it kak, kak, kak, kak. Others have called it cac, cac, cac, or cuck, cuck, cuck. It is rapidly uttered with considerable emphasis. As the female leaves the nest she sometimes gives a loud scream of fright or anger.

Field marks.--The Cooper's is a larger edition of the sharp-shinned hawk and easily confused with it; there is no well-marked color difference, though the adult Cooper's has a more clearly defined black cap. The chief difference is that the sharpshin has a square tail and Cooper's a rounded tail. Both have short, rounded wings and long tails, much longer than the Buteos; and both have characteristic Accipiter flight, a few rapid wing strokes, alternating with short periods of swift gliding. As seen from below, both may be distinguished from the goshawk by the more conspicuously barred tail and primaries. A small male Cooper's appears to be not much larger than a large female sharpshin, but Dr. George M. Sutton (1928) has shown that the average male Cooper's weighs about twice as much as the average female sharpshin.

Fall.--Cooper's and sharp-shinned hawks make up a large part of the great fall flights of hawks that pass over the United States in September, but they are often accompanied by ospreys and the Buteos. They fly high and seem to prefer to fly when the wind is from the northwest. Otto Widmann (1907) says that in Missouri "wholesale migration has been noticed from about the twentieth to the twenty-sixth of September, when singly or in pairs they have followed each other at intervals of a few minutes, from ten to twenty being visible to the spectator, but, as they are known to advance in a broad front, the whole movement must mean the depopulation of a large district."

Cooper's Hawk* Accipiter cooperii

*Original Source: Bent, Arthur Cleveland. 1937. Smithsonian Institution United States National Museum Bulletin 167: 112-125. United States Government Printing Office