By Stephen Jones and Ruth Carol Cushman, Special To The Daily Camera
Heavy October and November snows, along with frigid temperatures in the Northern Plains, have contributed to a modest influx of ferruginous and rough-legged hawks into Boulder County. Throughout November, we saw several of these large grassland hawks hunting around Lagerman Reservoir, Boulder Reservoir and in the grasslands north of Rocky Flats.
During the 1980s and 1990s, wintering ferruginous and rough-legged hawks were considered fairly common on the plains of Boulder County. Since then, urbanization, reduced numbers of jackrabbits and prairie dogs, and global warming have contributed to a steep decline in reported numbers of these open-country specialists.
Ferruginous hawks, named for the rusty feathers on their legs and shoulders, typically nest on broken cliffs in grasslands and prey on large rodents. We’ve seen adults huddled over just-captured prairie dogs and then screaming as bald eagles swoop down to steal their prey.
North American nesting populations have declined in areas where grasslands have been fragmented by highways, gas and oil drilling, and non-native vegetation.
Rough-legged hawks nest in the Arctic and typically prey on small mammals such as mice and voles. They migrate south in winter, searching for snow-free areas where they can hunt these smaller prey. Global warming has pushed the winter snow line northward, stimulating hawks who once wintered in Boulder County to winter in Nebraska and Wyoming instead.