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Pair Bond
It is typical for a male Cooper’s hawk to establish a territory and seek a mate during his second year. The defended territory is about half a mile in diameter. Often the female is an immature, in her first year. When the male attracts a female, he offers her food, sometimes bowing in an attitude of submission; if she accepts, the pair bond has begun.
Established pairs return to their nesting territory at the first hint of spring, the male usually arriving first. As far south as Texas, they arrive in mid-February. The season begins around the first of April in southern Canada. There is only one brood per year. They may return to the same nest used the previous year if the nest was not damaged by the winter weather. Most years the pair will pick a location in close proximity to prior nests and build anew. Nest-building begins soon after both members of the pair have returned and have begun bonding. This is a seemingly joyous time for the pair, as they sing their dawn duets and fly in tandem, swooping down together and then upward toward the nest area. The hawks mate frequently until all eggs are laid.
Nest
The nest site is usually a tall tree, either evergreen or deciduous, with good canopy, situated among other trees and often beside a stream or open area. A fork in the upper branches of the tree, 30 to 50 feet from the ground is chosen. Here a platform nest of sticks will be constructed. The male normally selects the site and does most of the nest-building, although the female occasionally adds a stick to the nest. They snap off fresh sticks from a tree with their beaks or pick them up from the ground. Most of the nest construction is done in early morning, in fair weather, an endeavor that takes about two weeks. Typically, the hawk will fly low until it reaches the nest tree, then zoom upward, using its tail like a rudder, flying to a point just above the nest site, then zeroing in through some opening only he can see. If the nest and/or eggs are destroyed before there are hatchlings, the hawks will typically select another location and build again, in as short a time as four days. Cooper’s hawks have been known to use an old squirrel or other bird nest as a base. The bowl of the nest is lined with outer bark torn off of nearby trees. Fresh greenery is often added to the nest. The nest is typically 24” – 28” in diameter and at least 6” deep, barely large enough to house the female, and is seldom perfectly round, sometimes taking on a conical or triangular shape. Frequently the long tail of the female can be seen sticking out of the nest.
Egg-Laying and Incubation
The first egg is laid around the beginning of April in the south, mid-May in the north. Hawks nesting in an urban area typically lay more eggs than rural hawks. As many as seven eggs have been reported, but even a clutch of six is rare. The usual clutch size is three to five eggs, elliptical in shape, smooth, and about the size of a hen egg. The color is pale blue when laid but by hatch time, hardly a trace of blue remains; faint buff-colored streaks and spots may linger. The female, who has a brood patch, does almost all of the incubation, leaving her nest only to eat, defecate, and preen. The male lacks a brood patch but does incubate the eggs whenever the female is absent. The male provides all food to the female during this time. Incubation normally begins after the third egg is laid.
The first three eggs normally pip in 34 days. By the time hatch is complete, around 36 days, the fourth egg has pipped. A fifth hatchling may survive, or may starve or smother in the nest. Any nestling that dies will be fed to its siblings. Normally, the majority of the hatchlings are males.
Hatchlings
Hatchlings are altricial and covered with white natal down. They can move about the nest well enough to turn and slice outside the nest within hours after hatch. They are dependent on the parent birds for food and warmth, however. The female alone broods her young, and does not tolerate the male on the nest. The male hawk continues to provision the nest, plucking and delivering food to the female at a nearby rendezvous branch. The female tears small bits of food from the prey and feeds the young bill to bill in an efficient manner. The nestlings form an orderly semi-circle before her and sit in feeding position, awaiting their turn. Aggressive behavior between siblings is rare; given an abundance of food, even a fifth chick has a fair chance of survival.
Development of Young
Within ten days of hatching, a second coat of thermal down, longer but still buffy-white, grows from separate follicles. At this point, the nestlings are capable of thermoregulation, and the female does not need to brood them continuously. At 16 days, the chicks are moving about the nest and begin peering out at the world below with blue-grey eyes that will soon turn yellow. By the third week, juvenile feathers have begun forming on their wings and tails, and self-feeding has begun. At 23 days, the first dark feathers appear on their heads. Tiny dark patches of auricular feathers protrude over the ears, giving the young hawks a comical appearance when viewed face-on.
Even after the young hawks no longer need to be brooded, the adult female guards them continually from a nearby perch. The nest of young Cooper’s hawks is kept tidy by their mother, who removes egg shells and other waste. She caches uneaten food on the branch of a nearby tree, for later consumption. She simply eats any parts of the prey that are too bony or difficult for the young birds to get down. She canvasses the feeding area for uneaten tidbits, effectively “sweeping” the nest after each meal. All of this changes once the young hawks are large enough to self-feed, at which time the nest becomes littered with partly-eaten pieces of prey. An average of 66 prey items will be required to raise each chick to six weeks of age.
By 25 days, the male chicks begin to venture out beyond the nest to supporting limbs, hopping and fluttering their wings in their first attempts at flight. The females typically require more time in development, perhaps three days. In the nest, they flap their wings and leap at the tree trunk or any available twig, in a practice known as “footing,” readying their feet and talons to grasp and balance. It is not unusual for one young hawk to bounce off a branch into the nest and land squarely on top of one of his siblings, who seems to shrug off the offender with good humor. The siblings compete for prey deliveries, mantling with their wings to claim and guard their food, which nevertheless can be stolen quite easily, without much of a squabble. Even though the young hawks are self-feeding by this time, they still occasionally line up in a semi-circle like school children to be fed by their mother.
Fledglings
At 31 days, although flight feathers are little more than three-quarters grown and down still clings to their heads, the young hawks hop and fly about in the nest tree, even fluttering to the branches of adjacent trees, all the while whistling their calls eee-eew eee-eew. The fledglings continue to return to the nest for food and rest for another week to ten days. During this time, both parents hunt to satisfy the needs of their hungry family. The adult male is now free to frequent the nest, and sometimes will deliver live prey, presumably to teach the fledglings how to kill and pluck prey on their own. It is not unusual to see the adult male bringing prey to the nest, with one or more of the young birds flying in hot pursuit right behind him. In this case, he makes a hasty retreat. By this time, the fledgling hawks are nearly grown, and the nest is a tight fit for bedfellows so large. The young hawks solve this problem for themselves, however, by stretching out side by side, like sardines in a tin. Before long, the older ones begin to roost at night, and the nest is used less and less.
The young fledglings frequently spend time together, hopping from limb to limb and chasing each other. They appear to be playing although their games may be motivated by curiosity and stealing tidbits of food from each other. It does not take them long to figure out where their parents’ plucking stations are, and they will fly, squealing, from those points to the nest to be first in line, often arriving at the wrong place at the wrong time.
When the fledglings are around 45 days old, food drops into the nest cease, and the parents begin encouraging them to fly further afield. At around 51-54 days, their flight feathers are full length, and by 56 days the feathers are hard-penned. They are now juveniles, and they are capable of hunting on their own without injuring themselves. All they lack is experience, a critical factor in the first year of the young hawks. Only 22% - 28% will survive the first year. The oldest recorded age is 12 years, and the maximum age for a breeding female is 9 years.
Next Chapter: Tracking
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