Coopers Hawk
The Cooper’s Hawk, Accipiter cooperii, is normally a secretive bird, seen only as it streaks though an area in pursuit of prey. They have been fairly common on power lines for the past month or so, allowing a detailed look at their beautiful plumage.
More colorful than most raptors, the Cooper’s Hawk is a medium sized, bluish gray raptor with white bars splashed horizontally across its reddish brown breast. It is born with gray eyes, which go though stages of orange before reaching the intense red of a fully mature adult.
Like other accipiters, it is a bird of wooded areas, equally at home in both deciduous and pine forests, in both rural and urban areas. Its short, rounded wings are designed to help it avoid branches. Its long tail helps it maneuver sharp turns at high rates of speed in dense woods.
Squirrels, chipmunks, and mice make up a large portion of its diet, augmented with occasional snacks of reptiles, amphibians, and large insects. Its favorite food, however, is songbirds, especially subadult American Robins and Blue Jays. It will also take birds as large as pheasants and crows.
Hunting from a concealed perch, the Cooper’s Hawk attacks unwary prey. Appearing out of nowhere like a Stealth bomber, it snatches the animal and squeezes it to death.
Cooper’s Hawks are regular visitors to my yard, and have on occasion mistaken my bird feeder for a fly through restaurant. Flashing through my feeder area in hot pursuit of a tasty songbird, they do not slow, even when their prey darts into a tree for cover. In spite of their adaptations to this type of hunting, a recent study showed that 23 percent of Cooper’s Hawks had signs of healed fractures of the chest bones. Undoubtedly, many others suffered injuries too severe to recover from.
The young are clumsy and comical as they try to catch birds much smaller and more maneuverable than themselves. The adult birds are successful in only 1 try out of 10; the success rate for juveniles is much lower.
In earlier times, the Cooper’s Hawk’s habit of feeding on chickens earned the wrath of family farmers. Nicknamed the Chicken Hawk, farmers often killed them to protect their flocks. These killings, along with habitat loss and pesticide use, led to steep declines in much of its range.
Corporate farming has shifted chicken production to large, enclosed sheds. Raptors are now protected and can no longer be shot. Trees are reclaiming much of the east and the pesticide DDT has been banned for use in the United States. These changes have led to a rebound in Cooper’s Hawk numbers, but they are still experiencing problems in the drought stricken West and portions of the East. They are listed as endangered in Wisconsin and Illinois.
Minnesota has a relatively healthy population. Breeding throughout most of the United States, birds found here are partial migrants and spend winter just to the south of us. Birds found in areas south of Minnesota stay put year round.
Animals often show a difference in size between genders, usually with the males being larger than the females. This is called sexual dimorphism. In the accipitrids, most show at least some amount of reverse sexual dimorphism, in which the females are larger than the males. This is more pronounced in birds that prey on other birds. It has been speculated that the size difference allows each gender to seek out different prey in different habitats.
Incubation may also play a role in this size difference. The female does the majority of incubation, with the male sitting lightly on the eggs only while the female eats the prey he brings her. Animals with larger bodies can handle cold weather better. Because most raptors begin nesting in late winter, this size difference offers an advantage to egg survival.
Nests are built of twigs high in the crotch of a tree. Starting a nest in cold weather requires that eggs be incubated as soon as laid in order to avoid freezing. This results in different hatching times for the 2 to 4 eggs, and different sized young. The younger birds often die of starvation due to their inability to compete with their larger siblings.
Many of us express hatred for this bird because it eats our beloved songbirds. Nature, in her infinite wisdom, intended for this to happen. Songbirds have many babies through the course of their lifetimes. If all these babies were to survive, there would not be enough food for them and most would perish. Raptors assure a healthy songbird population level.
We, also, could perish without the important service that this raptor and other predators provide. Songbirds and other small animals such as rabbits, rats, and mice eat the same grains we depend on for survival. If their populations were not controlled by predators, our crops would be smaller, our plates less full, and our overall health poorer. The next time you lean back in your chair with a belly full of tasty pasta or bread fresh from the oven, thank our raptors.
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