Ferruginous Hawk
Last Update/Review: June 17, 2002
Status | Description | Habits | Reproduction | Food | Limiting Factors | Management and Outlook
Status
In the Alberta Wildlife Act the ferruginous hawk is classified as an endangered animal. Historically, ferruginous hawks nested throughout the prairie and arid grassland regions of western North America. However, since 1900 their numbers have decreased throughout the region. The number of ferruginous hawks in North America has fallen to only one quarter of the previous estimated population. In Canada, this species is found now in approximately 50% of its earlier geographic range. It is no longer found in southeastern British Columbia and the number of birds in southern regions of Alberta, Saskatchewan,and Manitoba is greatly reduced.
In the early 1900s, ferruginous hawks nested throughout south and central Alberta as far north as Edmonton, but by 1987 nesting birds were found no farther north than Coronation (60% of the earlier range). The population in Alberta is estimated at 1800 breeding pairs, which may represent 65% of the Canadian population and 35% of the North American population. Ferruginous hawks are found in areas of uncultivated pastureland or prairie.
Description
Ferruginous hawks are the largest of the hawks soaring in North America. The adults are heavy, thick-set birds with broad powerful wings. Ferruginous and rough-legged hawks are the only hawks whose legs are feathered down to the toes. Adult female ferruginous hawks may be up to one third larger than adult males. Ferruginous hawks have a natural range in colour, from very dark to light.
The
name "ferruginous" comes from the Latin word ferrugo,
meaning rust. Most ferruginous hawks in Alberta can be recognized as
large, light-coloured hawks with rusty brown on their shoulders, back,
rump, and legs. In flight, their legs look like a dark 'V' against
the white belly and underparts. The underside of the tail is unbanded.
It is light grey throughout.
Dark phase ferruginous hawks are dark brown with some feathers edged in rusty brown. The tail differs from grey to grey-brown and is unbanded. In flight the underside of the wingtips and the tail appear much lighter than the rest of the body.
Habits
Ferruginous hawks are birds of the arid grassland regions of the province. Along with burrowing owls, they are the only raptors (birds of prey) that use the grasslands as their main habitat. The large body and broad wings of ferruginous hawks are well adapted to soaring on thermal updrafts over the prairies or giving a rapid straight-a-way chase of prey animals. They are completely unsuited to dipping and turning among trees or shrubs in habitats with heavy cover.
Like most of our raptors, ferruginous hawks are found in Alberta only during the summer months. Generally, they arrive in late March, nest and raise their young from mid-April to late July, and migrate southwards in September and October. Ferruginous hawks banded in Alberta have been found wintering in Colorado, New Mexico, Kansas, Texas, and California. Each year individual birds return to the same nesting area and often, the same nest.
Reproduction
Like the birds themselves, nests of ferruginous hawks tend to be big and bulky. A pair of birds may use a nest repeatedly and add new material each year. Nests up to 1.5 m wide and 3 m deep have been recorded. The nests are built largely of sticks and roots and are often lined with dead grass, sod, or occasionally paper. Cow dung is found in most nests and is characteristic of ferruginous hawk nests. As the dried dung breaks down, it provides a soft lining for the nest.
In Alberta, most ferruginous hawk nests are isolated trees (75%) or on rocky ledges (20%) or on the ground (5%). Most often the nests are on a high spot overlooking a large open area. Nests on ledges or on the ground are often situated where some natural shade from the hot summer sun is available. In other cases, the female bird provides shade for the young by standing with her back to the sun and her wings partially spread. Heat stress can be a serious problem, particularly for very young birds.
Ferruginous hawks usually mature at three years of age and may live up to 15 or 20 years in the wild. When they return in the spring, male birds establish a territory close to where they were raised. The female then chooses a nest site. Both birds are involved in building or renovating the nest. A breeding pair may have up to five nests in their territory but use only one each year.
Female ferruginous hawks lay three to five eggs and incubate them for approximately 30 days. The eggs hatch about the same time as young ground squirrels become active above the ground. The male bird provides all the food for the female while she incubates the eggs and protects the young birds. Since he must provide food for both adult birds and up to five growing youngsters, it is important that the nest is in an area which is familiar to the male. As the young birds grow larger, both adults hunt and bring food to the nest. However, only the female actually feeds the young. The ability to raise young depends largely on the availability of food throughout the nesting period.
Food
Ground
squirrels make up nearly 90% of the diet of ferruginous hawks in Alberta.
This is not surprising, considering the hawks' adaptations for living
in grassland habitats in open country. Migrating birds return in the
spring just as ground squirrels are becoming active after their winter
hibernation. Ferruginous hawks hunt during the day when ground squirrels
are active. While raising their young, one pair of ferruginous hawks
consumes an average of 480 ground squirrels. In Alberta, they may also
take a few voles, mice, and white-tailed jack rabbits.
The hunting techniques of ferruginous hawks are well suited to flat, open areas. The most successful technique is a long, low flight close to the ground (similar to a northern harrier). This makes a large bird difficult to see and allows a quick direct strike on an unsuspecting ground squirrel.
There is less energy needed for high soaring flights, but such is used less often because the success rate of capturing prey is also lower. In addition, ferruginous hawks will use trees, hydro poles, or powerlines as they hunt from these perches. Other intriguing techniques used by these hawks include stalking or stealing up on ground squirrels (like a terrestial predator) or crouching at the mouth of a burrow and grabbing a squirrel as it comes out!
Limiting Factors
The
major problem for ferruginous hawks has been a dramatic decrease in
the amount of native grassland throughout their range. In recent years
the number of naturally occurring prairie fires has decreased and trees
and shrubs have invaded the prairies. In addition, the amount of grassland
which is cultivated for agricultural purposes, developed for settlement,
or used for resource exploration continues to increase throughout the
geographic range of ferruginous hawks. These changes interfere with
the hawks' ability to hunt and capture ground squirrels, their main
food item. Without sufficient food, the birds will not establish a
nest.
In areas where ferruginous hawks continue to nest, food does not appear to be a limiting factor. In these areas, the major problem seems to be a shortage of preferred nest sites.
Ferruginous hawks are disturbed easily by the activities of humans. They are most sensitive when the pair is establishing a nest, when the female bird is incubating eggs, or when she is protecting newly-hatched young (a time when the young birds are most threatened by heat stress). Human activity around a nest may result in the adults abandoning the nest or in the death of young birds. In Alberta it is illegal to kill or harass ferruginous hawks or disturb their nests at any time of the year.
Management and Outlook
Management of ferruginous hawks in Alberta has focused on providing safe nesting sites in areas of open uncultivated grassland where food is readily available. Tall nest poles or baskets placed in trees have been used successfully by breeding pairs. Over half of the breeding population of ferruginous hawks near Hanna in 1984 used artificial nest poles or baskets. These sites allowed a significant increase in the density of nesting birds in the area. Ferruginous hawks also will use powerline towers, haystacks, equipment sheds and even windmills as nest sites.
Human activity within 1000 m of active nest sites should be restricted, particularly between mid-March and mid-July, when the breeding pairs are most sensitive. After this time, adult birds are unlikely to abandon the nest unless the disturbance is excessive and repeated. However, care should be taken whenever you are near a nest.
The outlook for ferruginous hawks is quite bright. They have responded well to artificial nest sites and the success rate for rearing young is unusually high once a nest is established. High winds and severe weather will continue to cause some losses.
Ferruginous hawks can be abundant in open areas with short or thinly scattered ground cover. Thus, they can do well in areas where cattle or sheep are grazed and nesting structures are present. They avoid areas with greater than 30% cultivation and/or low ground squirrel populations.
Ferruginous hawks are extremely beneficial to landholders by removing large numbers of ground squirrels without the dangers associated with pesticides and other chemical control methods. However, in areas where pesticides are used, ferruginous hawks may be killed accidentally by eating poisoned ground squirrels. It is not likely that this happens often. In general, landholders in Alberta have a positive attitude towards ferruginous hawks.
Various groups and organizations also are interested in helping to conserve ferruginous hawks. Individuals, non-government agencies, and special interest groups can help with the nest poles or baskets. They may get involved by erecting new ones, maintaining existing ones, or replacing fallen ones. Information concerning ferruginous hawk activity and nesting success at any nest is also valuable for helping the Natural Resources Service manage this species. Please ensure the birds are not disturbed by your presence.
