Hawks

Hawks and their allies are members of the Accipitridae family.  We have several commonly seen species in DuPage County including Cooper’s Hawk and Red-Tailed Hawk, which are year-round residents and Sharp-Shinned Hawk, a species here only in winter.  Other species that may be seen in the area include Broad-Winged Hawk, a summertime only resident, Northern Harrier and Red-Shouldered Hawk, both seen year-round, and Northern Goshawk and Rough-Legged Hawk, also here only in the winter.

Hawks in our area are medium-sized birds, active during the day, with hooked beaks for feeding, and long, sharp talons for catching, holding and killing prey.  The Red-Tailed Hawk, Buteo jamaicensis, is often seen gliding on winds high aloft over open fields.  The  Sharp-Shinned Hawk, Accipiter striatus, and Cooper’s Hawk, Accipiter cooperii, are mostly seen zipping among the trees in open woodlands or in our backyards.

Hawks are among the top avian predators in this area.  They have excellent eyesight and can see clearly four to eight times farther than our human eyes.  As hunters in mainly terrestrial habitats, their coloring blends in with their environments.  Most are brown, grey or black, with pale underparts often streaked or barred in shades of brown.  Combining their coloration with their ability to fly very quietly, most prey are unaware of the hawk until they have already been set upon.  Hawks eat a wide variety of foods including other birds, mammals, fish, reptiles, amphibians and invertebrates. 

Many hawks show a distinct size difference between the sexes, with the female being larger.  There is no consensus as to why this difference exists.  In birds of the accipiter group, including Sharp-Shinned Hawk and Cooper’s Hawk, the males and females will select prey of different sizes and habitats.  This allows a mated pair to find food in two different ecological niches.  Members of the accipiter group feed mostly on other bird species and are just as well adapted to chasing smaller birds through open woodland areas as they are to attacking perching birds from available cover around backyard feeders.  Species in this group have long tails to increase maneuverability, particularly in open woods and forest edges.

Hawks in our area all mate for life, unless a partner is lost.  All species use display flights to attract a mate, and displays may be used by either sex.  Red-Tailed Hawks are unusual in that both sexes have display flights that are started individually, but end together.  Hawks in DuPage County are solitary nesters.  They actively defend the territory that includes their nest as well as nearby feeding habitat from other hawks of their own species.  Nests are built from vegetation, mostly sticks, and a pair may have more than one nest in an area, and nests may be used for many years.  Switching among nests occurs if breeding fails or a nest is infected by parasites.  Whenever possible, fresh vegetation or pine needles are placed in the nest, possibly to provide concealment, serve as a natural coolant, reduce odor or fungal growth, or to signal that the nest is currently occupied.  Nests are further insulated with finer material to keep the occupants warm as well as to keep eggs from falling between sticks.  Nests are very important, and hawks tend to spend several weeks or months building and constantly improving them. 

As egg laying time approaches in early to mid-spring, males will keep supplying nesting material, as females construct and shape the interior.  Egg laying consumes a lot of energy, so females tend to lay an egg every other day.  The number of eggs in a clutch varies from two to six depending on species and tends to increase in breeding locations farther north.  Both male and female will incubate the eggs for a period of 28 to 35 days.  Incubation starts as soon as the first egg is laid, so earlier chicks may be born first and tend to be stronger than later chicks.  After hatching, males do most of the hunting, and females spend all of their time with the chicks.  Chicks can hold up their heads, open their eyes and feed by sight within minutes of hatching.  Females will wave a bit of prey in front of each chick until the chick snatches it from the mother’s beak.  If the bit proves too big for the chick to swallow, the mother may take it back and eat it herself and start with a new bit of prey.  In the nest, chicks are very susceptible to weather changes, and females will spread their wings to protect them from both rain and hot sun.

In northern Illinois, the Broad-Winged Hawk migrates to Central America for the winter.  Several species from summer breeding grounds in central Canada, including Sharp-Shinned Hawk, Northern Goshawk, and Rough-Legged Hawk, migrate into northern Illinois for the winter.  All migrating species fly during the day when winds are more favorable for long distance flight.  Juveniles and adults will fly at different times and different speeds, coming together at their destinations.  Some species may flock together, but most are solitary flyers.  However, none will attempt long water crossings, tending to follow land for the whole journey.  Fall migration starts in mid-August and lasts through November, normally on days following the passage of a cold front, when the air is cooler, drier and more stable.

Over the past few decades, hawks have faced a number of threats including hunting, pesticides and loss of habitat.  However, they have been able to adapt well to their changing environment.  Breeding bird survey statistics indicate that most species have seen increasing populations in the past twenty years, assisted by reduced pesticide use, increased dedication of rehabilitation facilities, and better education, altering the views of hawks held by the general public.