A huge influx of northern birds joins resident ferruginous hawks to feed on prairie dogs through the winter. Ferruginous means "rusty color" and refers to the coloration of the birds’ wings and legging feathers. These are the largest and heaviest of the North American buteos. They are about midway in size between other buteo hawks and the golden eagle. Females are larger than males, but the genders have similar plumage. Adults have both light and dark morphs (plumage types).

Light-morph ferruginous hawks are most common, and are distinguished by their light tail, and mostly pale undersides. In flight, the reddish feathers of the legs form a dark "V" against the white background of the belly and tail. A viewer can also look for telltale large dark comma-shaped patches at the wrists of the wings. When perched, the reddish feathers are still visible on the back and shoulders and white crescent-shaped patches on the primaries. The rare dark-morph birds are dark brown to cinnamon-colored over the body and head with a light gray or whitish tail, and light crescent patches on the wings, similar to light morphs. Juveniles birds are similar the light morph, but may have a lightly banded tail and lack the rufous legs and back.

Ferruginous hawks have legs feathered down to the tops of their feet. Only owls and two other North American hawks share this characteristic—golden eagles and rough-legged hawks. Scientists suppose that these feathered leggings help protect these birds from the bites of their rodent prey. Ferruginous hawks seem to prefer a prairie dog diet. They are most often seen perched on the ground beside a prairie dog mound, ready to nab a dog as it emerges from the burrow. Though ferruginous hawks are not dependent on prairie dogs, their populations have been impacted by dwindling prairie dog populations in some areas and loss of grassland nesting habitat to cropland and urban development. They are classified in Colorado as a species of special concern.

In flight, ferruginous hawks look very similar to red-tailed hawks—whose populations are also exploding on the plains this time of year. The telltale difference is that the ferruginous hawk's tail is white, while that of the red-tailed is a reddish-brown color. For red-tailed hawks, the tail is usually a given to identify the adult hawk—the state’s most variable looking species. Most adults are reddish-brown with a creamy breast and reddish belly band. But Harlan’s subspecies, which flies in from Alaska this time of year, is an almost solid dark brown. A rare morph, Krider’s subspecies, has a white head and under parts and a pale, reddish-tinged tail. When in doubt, listen. This hawk’s call is most often used by movie industry to represent the call of eagles and other birds of prey. It’s a long, drawn-out, harsh-toned keeeerrr!

A strictly winter visitor, rough-legged hawks are named for their completely white feathered legs, which look like they’re wearing a billowy pair of trousers. Rough-legged hawks have light and dark color phases and variations in between. The dark phase is less common. Adults generally have mottled light-and-dark feathers underneath, with dark patches at the wrists. Seen from below, the tails of both phases are light with a dark band at the tip. Seen from above, both phases appear mostly dark, but the light phase shows a light tail with a dark terminal band, and the tail of the dark phase appears dark all over. The adult male can have several dark bands at the tip of its tail while the female has only one band. The light phase has a distinctive light-colored head and dark wings and body. In flight the rough-legged’s wings form a dihedral, a v-shape, and the bird often hovers.

• Rocky Mountain Arsenal NWR—Site #62
• Bear Creek Lake Park—Site #54 
• Simla Pronghorn Loop—Site #12
• Chico Basin—Site #15
• John Martin Reservoir State Park and State Wildlife Area—Site #20
• Cathy Fromme Prairie Natural Area (Ft. Collins area)—Site #34 
• Trickle Mountain (near Saguache)—Site #139

(The Colorado Wildlife Viewing Guide, Second Edition, Revised is available at many bookstores, through our online store, or through the Colorado Wildlife Heritage Foundation.)