The Northern Goshawk is largest of the three accipiters at 19-26 inches in length and a wingspan of 40-48 inches. The female is significantly larger than the male. On average, goshawks weigh between one and one-half to two and one-half pounds.

The Northern Goshawk inhabits old-growth forests throughout the United States, Canada and northern Mexico. In most areas this raptor is a year-round resident; but in years of low prey numbers, goshawks leave their northern breeding areas "en masse" in search of more abundant food supplies. This event, which occurs with some regularity every eight to 11 years, is called an irruption and follows the population cycles of its main prey species - the snowshoe hare and ruffed grouse - in northern boreal forests.

In the Rocky Mountain region, the Northern Goshawk feeds on a variety of birds and mammals, including ground squirrels, cottontail rabbits, flickers and jays.

Goshawks begin nesting in late March or early April. Most pairs remain mated in the same territory as long as both birds are alive. Nest sites are usually located in mountain forests and are commonly found in riparian zones. Typically the nest is in a large, mature tree (especially aspen) as far up as 30 to 35 feet high. The nest is a bulky structure more than 30 inches across, made of large sticks. Two to four bluish-white eggs are laid in April, and incubated by both sexes for about 30 days.

Northern Goshawks can be observed migrating south from late August until late November. Under most circumstances, these migrating goshawks are primarily juvenile birds. But during periods of irruption, large numbers of adults can be observed, as was the case in 1983 and 1984 at the Goshute Mountains migration monitoring site in Nevada where hundreds of migrating adults were documented.

Because the goshawk depends entirely on extensive stands of mature, old-growth forests, this species is an excellent indicator of the health of our pristine mountain forests. As logging pressures increase, these birds may experience population declines as a result of severe habitat loss and degradation.