The Cooper’s hawk is a medium-sized hawk that is found across much of North America. It is known for its swift flight and skill at catching small birds in dense vegetation. The underside of a Cooper’s hawk can reveal a lot about the age, sex, and color morph of an individual bird. Knowing the field marks of the underside can help birders accurately identify Cooper’s hawks in the wild.
Adult Cooper’s Hawk Underside
Adult Cooper’s hawks have striking color patterns on their undersides that help distinguish them from other hawk species. The markings also differ between sexes and color morphs.
Barred Belly Band
The main feature on an adult Cooper’s belly is a broad reddish-brown colored band that runs horizontally across the lower breast and belly. This belly band is made up of thin vertical streaks or bars, giving it a striped appearance from a distance. The barring helps break up the bird’s silhouette when viewed from below, providing camouflage as the hawk hunts amid branches and tree canopies.
The barred belly band ranges in color from a rich rusty red to a darker brick red. It contrasts sharply with the light nape and neck, which are finely streaked gray and white. The dark belly band is an important identifying mark of an adult Cooper’s hawk.
Male vs. Female
The undersides of male and female adult Cooper’s hawks differ slightly in size and color intensity.
Males have thinner, lighter rusty bars on the belly band compared to females. Males also have thinner streaking on the chest and vertical barring on the flanks that are lighter in color than females.
Females, in contrast, have a broader belly band that is a deeper, richer reddish-brown. Their chest streaking and flank barring are also darker and slightly heavier than males. The differences are subtle, but observable when comparing males and females side by side.
Light Undertail Coverts
Another distinctive mark on an adult Cooper’s underside is the light-colored undertail coverts. These feathers under the base of the tail are white to pale gray, with some light rusty barring. When the hawk is perched, the pale undertail coverts are easily visible beneath the darker tail.
In flight, the light undertail coverts contrast with the hawk’s darker wings and back, making them one of the most noticeable markings. This helps distinguishes the Cooper’s hawk from other accipiters and buteos, which have darker undertail coverts.
Immature Cooper’s Hawk Underside
Younger Cooper’s hawks have more brownish undersides with less distinctive patterning. It takes almost two years for them to acquire the reddish-barred belly band and other markings of an adult. However, some underside traits can help identify immature hawks.
Brown Streaking
Instead of neat barring, immature Cooper’s hawks have chaotic brown streaking and mottling across the chest and belly. The streaks vary in thickness and orientation, giving a messy, speckled appearance. The chest may appear somewhat barred, but the belly is more indistinct.
The brownish ground color is darker and duskier overall compared to the pale grays of adults. There are also fewer well-defined white undertail coverts in immatures.
Yellow Eyes
One key feature that distinguishes immature Cooper’s from adults is their eye color. While adults have a striking red eye, immatures have pale yellow eyes, sometimes with a hint of orange. This yellow eye color persists through their first year before darkening to orange-red as adults.
Variations in Plumage
There is some variation in the plumage of immature Cooper’s hawks based on age. Very young fledglings have largely plain gray-brown undersides with little streaking. By their first fall, the chest and belly streaking is apparent but remains brownish rather than rusty red.
As they mature through their first and second years, the barring gradually intensifies and takes on more of a reddish cast characteristic of adults. However, the full adult plumage is not attained until two years of age.
Cooper’s Hawk Color Morphs
Most Cooper’s hawks are classic gray-backed birds with reddish undersides. But approximately 10% are born with plumage coloration variants from the typical form. These color morphs also show some distinctive traits on the underside.
Rufous Morph
The rufous morph has rich reddish-brown upperparts rather than gray. On the underside, the dark rufous coloring becomes a lighter peach on the chest, with a variable amount of dark streaking. The belly is cream to buff-colored with sparse streaking. The reddish undertail coverts are an identifying mark.
Brown-backed Morph
As its name suggests, this morph has solid chocolate-brown upperparts and wings contrasting with a pale underside. The underside is white to buff with delicate dark streaking. The legs of this morph are noticeably paler than other Cooper’s.
Gray-Fronted Morph
In this uncommon variant, the upper breast is medium gray grading into the normal reddish bars on the belly. The gray chest band contrasts sharply with the white lower breast and reddish belly. The back appears normal gray.
Albinistic Morph
Very rarely, partially or completely albino Cooper’s hawks occur. An all-white bird lacks the normal pigmentation while a partially albino bird may show white patches mixed with normal coloration. The eyes are typically pale pink or red rather than the normal orange-red.
Conclusion
The underside field marks of a Cooper’s hawk can reveal a lot about an individual bird’s life history at a glance. Adult plumage features like belly barring and undertail color help distinguish them from other raptors as well as younger hawks. Subtle variations in size and color intensity separate males from females. And the occurrence of color morphs adds diversity to the typical plumage patterns observed in this widespread woodland hunter. Taking note of these underside traits can help birdwatchers more readily identify Cooper’s hawks while enjoying time in the field.
