Green Scene

An unexpected guest stopped by for dinner — a Cooper’s hawk

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I am used to hearing blue jays squawking around my house. The other day, however, it sounded like the entire tribe had been mobilized — and they were very agitated.

My husband very excitedly announced that there was a large bird in the backyard. With the exception of a female turkey that trotted around our backyard years ago, the largest bird that we generally see is an American crow.

I quickly looked out the window, and that was no crow! I grabbed my camera and took several photos through the window glass. Pictures taken through glass can be of poor quality, but these images were clear and I quickly sent them off to my bird guru, Don Torino, a naturalist and the president of the Bergen County Audubon Society.

He identified it as a juvenile Cooper’s hawk, also known as a chicken hawk.

That bird took its time fluttering around our backyard, but apparently did not find anything to entice it to remain. It finally flew off and has, unfortunately, not returned. I say unfortunate because I later learned that the Cooper’s hawk hunts small birds such as mourning doves (Zenaida macroura), and I would dearly like it to remove some of the doves that insist on visiting my bird feeder daily.

Despite being symbols of peace, the alpha dove will chase off all other birds, including other doves, even after it can no longer eat more seed.

The Cooper’s hawk (Accipter cooperii) was named in honor of William Cooper by Charles Lucien Bonaparte, a French biologist and ornithologist, who advanced knowledge of American birds. Cooper was an American naturalist, collector and conchologist (someone who studies only the shells of mollusks, not the living organisms).

Cooper collected a specimen of the hawk named in his honor in 1828, and his many other specimens were of great help to the better-known figures such as James Audubon. Cooper also was one of the founders, in 1817, of the New York Lyceum of Natural History, later renamed the New York Academy of Sciences.

Amusingly, Bonaparte also was the namer of the mourning dove genus Zenaida in honor of his own wife.

Cooper’s hawks are not very large birds. Male weights range from 7.8 to 15.5 ounces, and lengths of 14 to 18 inches. In the animal kingdom females are usually smaller and lighter than males (sexual dimorphism). But one of the outstanding characteristics of this bird is that the females are both significantly larger and heavier than the male. Female weights range from 12 to 25 ounces, and they measure between 17 and 20 inches long.

Apparently, Cooper’s hawks are hard to distinguish from sharp-shinned Hawks (Accipter striatus), even for experienced birders, due to overlap of size and coloration.

It was once thought that these birds avoided settled areas, but apparently they are not that uncommon since smaller birds they prey upon abound in cities and towns. Said prey includes robins, jays, pigeons and woodpeckers, and they are aware of the availability of small birds in the vicinity of birdfeeders.

They also will eat bird eggs and small mammals such as squirrels and chipmunks. They hunt by approaching prey stealthily from cover and then bursting out.

They also hunt on the wing, and are sometimes trained for falconry.

Cooper’s hawks can be found in southern Canada, the continental United States, Mexico, Guatemala and Belize. Those from the eastern United States overwinter in southern and central parts of the country, while those from the western states overwinter in central and southern Mexico.

Partners in Flight estimates there is a breeding population of 700,000 birds, with the bulk of the population spending some time in the United States, 22 percent in Mexico, and 8 percent in Canada. The birds generally migrate individually, with the juveniles migrating earlier than adults, and females earlier than males.

The reverse is true in the spring — adults before juveniles and males earlier than females.

The population was under pressure from hunting and eggshell thinning caused by DDT. However, DDT was banned in 1972, allowing the population to rebound, and it’s not considered endangered. The total population has been estimated to be as high as 1 million birds.

One particular and intriguing Cooper’s hawk tidbit is the changes in eye color that this bird undergoes during its lifetime. The eyes of nestlings are bluish-gray, the juveniles have yellow eyes, while the adult eyes are red. Colors tend to be dramatic because birds do not have white around the iris.

Eye color can be caused by both pigments and light refraction. The responsible pigments include pteridines, purines and carotenoids. In addition to aging, eye color in many birds can change during the breeding season.

I imagine that Cooper’s hawks would be very welcome in those areas where pigeons abound!

Have a thought or comment for Sura Jeselsohn? Email her at greenscenesura@gmail.com.

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