Ferruginous Hawks found through out the Great Basin breed primarily in the eastern Great Basin and occur through out the nest survey area. This open lands raptor nests mainly in scattered junipers or on the fringes of larger stands. Constructed from sticks, often bigger than sticks found in other raptor nests, these large nests (often greater than a meter high) may dominate trees scarcely twice the nest height. The shear weight of these mammoth nests can cause the nest to topple over, spilling to the ground. Formed into the nest crown is a cup lined with pieces of brush and dung chips that may be relatively small.

Historically, Ferruginous Hawks nested on the ground as well as in trees. Although we have a number of known nests atop outcrops, sloped hills and low ridgelines, only two known nesting attempts have occurred on such substrates during the survey. Only one of these was successful. A ground nest on a slope with a small rock protrusion yielded one nestling in 2005.

During the non-breeding season, Ferruginous Hawks disburse widely through out the Great Basin and return to breeding areas in late winter. Incubation lasts 32 to 33 days and 38 to 50 days pass from hatching to fledging. A standard clutch is two to four eggs. With breeding initiated in early spring, most fledging occurs by mid summer.

Utah Ferruginous Hawk Occupation and Nest Starts

The number of known territories, occupied territories and active nests (nest starts) represent all Ferruginous Hawk nests monitored in Utah from 2001 through 2005. More than one nest is frequently present in a territory, an area held by a mated pair during a breeding season. In Utah, the number of nests in a known territory averages between two and three, but as many as 15 nests have been found in a territory. Behaviors of the adults clue surveyors to whether or not a territory is occupied and if a nest start has been initiated. Activities associated with occupation include the courtship behaviors of dual perching and soaring, copulation, prey exchange and nest building. Once actively nesting, adult behavior can be illusive with territorial flights high above the nesting area and the incubating adult sits cryptically, superbly blending into the nest edge. Since they are not perch predators like Red-tailed Hawks they may not be prominently perched in the immediate area of the nest. They range over open areas, occasionally seen hunting kilometers away from the nest.

Utah Ferruginous Hawk Success and Productivity and Nest Fledgling Production

Nestling development and behavior cues indicate nestling age and probable fledgling dates. The pre-fledged nestlings often are active at the nest, standing, playing with sticks or exercising their wings (hop-flapping). They are mostly covered with feathers, except for small patches on the back of their head and under the wing pits. A nest is considered successful once nestlings have reached at least 80% of the species median fledgling age (35 days for Ferruginous Hawks). All nestlings reaching at least 80% of the mean species fledge age are considered to have fledged, unless observations indicate otherwise. Most mortalities discovered after the 80% fledge age appear to have occurred outside of the nest, post-fledging. Once fledged the young birds stay in the area immediately about the nest for a few days. They are limited to the ground and low perches as they develop flight abilities.

Utah Ferruginous Hawk Trend

Due to the extensive location information on historic nests existing prior to HWI's survey efforts, the number of known nests increased only slightly during our initial five year survey. The number of occupied territories rose from 2001 through 2004 only to drop in 2005. Interestingly, the number of nest starts increased again, as it has in every year except in 2002. The record high nest starts in 2005, the slightly higher fledgling success rate and high fledglings per successful nest rate contributed to the record high production of fledglings in 2005. As with several other Great Basin Raptor Nest Survey focal species, the wetter end of the area wide drought cycle may be a large factor. For more information on Ferruginous Hawk nesting please see our state specific reports, Northwest Utah Nest Survey and Northeast Nevada Nest Survey.