For many years, we have been awed by the beauty and acrobatics of Prairie Falcons. During our many hours of research and bird watching, we have seen these birds courting, nesting, and capturing small birds and mammals. Sometimes we have seen them simply watching other birds and people approach their commanding perches. Other times we have also experienced these birds swooping down on us, just narrowly missing our heads.

It is exciting to watch the eggs hatch and the young grow and begin their life in flight. We look forward to banding the young and adult birds; it is always thrilling to handle these fascinating creatures. Perhaps the most pleasant part of all is simply sitting and watching Prairie Falcons from dawn to dusk and from season to season.

Our fascination with the Prairie Falcon has prompted us to write a book on this magnificent bird. Prairie Falcons are just as fascinating as their cousin the Peregrine Falcon; however, little has been written, in a popular form, about its life history.

Our purpose is to provide information to people interested in the Prairie Falcon and other birds of prey. In the first part of the book, we present observations on the Prairie Falcon's life history. We start by describing how it is related to other raptors. Then we examine the bird's behavior, interactions, and habitat. After discussing its characteristics, we describe its hunting habits and what it eats. Next, we follow the Prairie Falcon through the different seasons and describe their arrival on nesting areas, their courtship and nesting behavior. We also follow the young through their development and dispersal and discuss the information available on migration and winter ranges.

Finally, we look at people and the Prairie Falcon. We discuss falconry, especially as it relates to Prairie Falcons, examine the impact of pesticides and habitat destruction, and explore captive breeding and habitat mitigation. We then highlight a few of the many research projects on Prairie Falcons and how these studies help us understand this magnificent bird. In the appendix we discuss the etiquette everyone should observe when visiting Prairie Falcon nests.

We hope that this account of the Prairie Falcon excites your interest. We also hope that knowledge of and interest in the Prairie Falcon will aid in the conservation of this fascinating species.

Journal Entry, 28 May 1984

Today we are attempting to trap Prairie Falcons on North Butte, in Campbell County, Wyoming. We hope to attach radio transmitters on nesting Prairie Falcons in order to study their movements and habitat use. As we reach the cliff, winds are light and the sun is just rising above the butte. Conditions are perfect for trapping. The falcons are nesting on a lo-meterhigh cliff that rims the butte. By leaning far over the cliff edge, we can see three pure white hatchlings huddled in the falcon's eyrie. The down-covered young lack any feathering, so we estimate they are only one week old. Both adults spot us and begin to call while they circle high overhead. The adults grow more agitated and dive repeatedly in an attempt to drive us from their cliff. To capture the adults, we perch a live Great Horned Owl near the eyrie and surround it with mist nets hung from poles. Thus, when the falcons attack the owl, they should become ensnared.

5:50 A.M.—The trap is set. The owl is calm, but the falcons are nowhere in sight. We are hiding in a small grove of limber pine approximately loo meters from the trap. After a few minutes, we hear something that sounds like a sail ripping under tension. Looking up, we discover the sound is coming from the wind screaming through the feathers of a Golden Eagle as it dives toward our owl. We immediately sprint toward the trap, knowing the nets are not designed to capture Golden Eagles. We fear for the owl's safety, but quickly realize the futility of reaching the trap in time, so we stop and watch. Now only

70 meters away, it seems certain the eagle will crash through the nets and kill the owl. At that same instant, we notice a male Prairie Falcon diving toward the eagle. The falcon, which appears no larger than a dove compared to the massive eagle, is rapidly gaining on the eagle as it pumps its wings in a vertical stoop. The eagle, unaware of the approaching falcon, drops its talons as it plummets toward the owl. With astonishing speed, the falcon overtakes and strikes the eagle on its hind neck. The eagle with its talons still distended pulls up from its dive in staggered flight. The small falcon rebounds high over its eyrie, calling defiantly....

Although we never captured any Prairie Falcons that day, we did renew our appreciation for their flying ability and indomitable courage. No other bird in the western United States matches a Prairie Falcon's aerobatic ability, except possibly its larger cousin, the Peregrine Falcon.

When people think about falcons, they often envision these legendary hunters dropping from the sky, attacking prey during high-speed stoops. The hunting prowess of falcons has fostered a kinship with humans throughout the centuries. Medieval kings and queens valued Peregrines, Gyrfalcons, and Merlins as courageous hunters, capable of killing quarry during highspeed chases. Prairie Falcons are also capable of high-speed attacks; at other times, Prairie Falcons simply drop from an elevated perch to grab a mouse.

Prairie Falcons have shared the open plains with Native Americans for centuries. Their feathers decorate the shields of ancient warriors, and falcon petroglyphs are a testament to Native Americans' respect for the species. Early settlers also watched Prairie Falcons as they drove their wagons across the high plains.

Prairie Falcons draw bird watchers, falconers, and, sadly to say, poachers, who feel it is sporting to shoot these magnificent creatures. Today, some populations are being subjected to illegal shooting and other activities, such as mining and development, that reduce their habitat and food supply.

Along with being very maneuverable and fast, Prairie Falcons can be quite aggressive. They may tolerate a Great Horned owl's nesting nearby for several weeks and then suddenly attack the nest, killing the owl's young. These birds of the western plains are exciting to see during all seasons.

The Prairie Falcon is indeed a bird of contrasts. It can remain very quiet and complacent, blending into the background while perched in a tree or cliff. At other times, it can be a terror to its neighbors. When a falcon is unsuccessful in driving away an intruder, such as a human, it may mercilessly attack previously unmolested birds in order to vent its frustrations. Other birds nesting near breeding falcons may be left alone for long periods of time and then suddenly be subjected to a violent attack.

Prominent rocks near falcon eyries that are used as perch sites are often stained white from droppings. These "whitewash" areas can be seen from long distances and are frequently the first clue that falcons are present. Prairie Falcons readily defend their nest sites from intruders, occasionally striking and even drawing blood from persons venturing too close. More often, Prairie Falcons swoop within inches but rarely make contact. The swooshing sound of the wind through their feathers is usually convincing enough to frighten intruders to take cover. Attacking falcons show no mercy, whether a person or other animal is approaching the nest. Prairie Falcon's aggressive attacks on birds, such as barn owls and eagles, and on mammals, such as coyotes and fox, have all been successful in driving away intruders.

A Prairie Falcon researcher in Idaho, Anthonie Holthuizjen, observed thousands of aggressive interactions at thirty-seven nest sites. He found that each Prairie Falcon pair averaged six interactions per observation day. Aggressive attacks were highest just prior to egg laying. During incubation, the number of interactions declined but again increased about the time the eggs hatched. They declined again during early brood rearing but increased as the chicks aged. These interactions may be related to the amount of time falcons have available to perch and guard their territory.

Some Prairie Falcons may form pair bonds for life. This is based on studies that show the same pair of birds return to the same eyrie year after year. However, some females return to the eyrie each year with different mates. Other times, both pair members find a new mate. When a mate is lost during nesting or brood rearing, that bird is often replaced by a bird that was unable to breed because it lacked a territory.

Raptors

The general term raptor (from the Latin word rapere, meaning "one who seizes") includes all birds of prey. Raptors are flesheating birds that include falcons, hawks, vultures, eagles, and owls. Raptors typically have powerful feet with talons, hooked beaks, and keen eyesight for capturing and killing prey.

Falcons belong to the order Falconiformes, which also includes other diurnal birds of prey, such as eagles, hawks, buzzards, kites, harriers, ospreys, secretary birds, and condors. Falcons are classified in the genus Falco, which means they share certain characteristics that distinguish them from other raptors. Strigiformes consist of two families of owls, which are distinguished from other raptors by their large heads and forward directional eyes. The family Tytonidae includes 11 species of barn owl worldwide, whereas the family Strigidae includes 134 species of owls.

Vocalization

Prairie Falcons scream in a high-pitched voice. When birds approach their cliffs in the spring, they often emit a series of rapidly repeated cacks, or notes of varying pitches. Sometimes the notes are very spirited; others are very soft. Male cacks tend to be higher pitched than those of females. However, females and males cannot always be distinguished by their calls.

When people approach a nest site, the alarm note is a high, repeated kee-kee-kee, almost like a cack. Another note that the birds sometimes repeat is a rattling, such as a kr-r-r-r. Toward the end of this vocalization, the note often increases in volume. The birds also use another whining note called kruk-kruk. A distinct area around the nest is defended, and when intruders cross the line, the male or the female will emit alarm calls. While one member of the pair is vocalizing, the other may be swooping down, attacking the intruder. Other attacks may come without any type of vocalization whatsoever.

Coloration

Adult Prairie Falcons are found in several color phases—from light to dark with a series of gradations in between. Most of the time, the different color phases occur in different geographic areas. The exact reason for the color phases is not known.

At hatching, young Prairie Falcons are covered with a fine white down. In about two weeks, darker feathers appear, and after twenty-one days, noticeable feather tracts emerge. Recently fledged birds are colored dark above and light with speckles below, which is distinct from adults. Final plumage growth and the last shedding of down takes place at about two months of age as the young start to fly. At this stage the young falcons are buffier and more striped than the adults, with a more reddish tinge to the upper parts. The eye color of young falcons is brown, and their feet and legs are slate colored with black claws. The beak is bluish black, and a slight yellow tinge appears under the base of the mandible. The young assume a lighter color as they mature and are virtually identical to the adults by the end of the first summer.

Size

Male Prairie Falcons are 37-38 centimeters in length and weigh 500-635 grams. Females, on the other hand, are 45 centimeters in length and weigh 762-970 grams. Their wing span is up to 105 centimeters. Thus, observers can easily distinguish the male and the female in the field when both sexes are together.

Body Size and Life History

Ian Newton shows how various life-history parameters of raptors are correlated with body size. He points out that small raptors—kestrels, for example—usually mature early and often breed in their first year. They have large clutch sizes of four to six eggs and short breeding cycles of less than three months. Their life span is short, often less than ten years, and they have a fairly high annual mortality rate—40-50 percent. On the other hand, larger birds, such as condors, are slow to mature and often breed as late as five years of age. They typically have smaller clutch sizes, often consisting of only one egg, and longer breeding cycles, which take more than twelve months. The condor's life span is usually more than ten years and its mortality is generally low, around 5 percent. Medium-sized birds such as the Prairie Falcon show intermediate life-history characteristics.

Life-history strategies also impact population trends. Because of their high birth rate, populations of small-bodied species can quickly colonize an area if changes in nest sites or prey abundance become advantageous. On the other hand, the large-bodied raptors have a slow turnover and are usually more stable. They tend to select areas where the prey base is constant. Newton notes another trend: tropical raptors of equivalent size to temperate raptors have a lower breeding rate. Presumably, then, the tropical species also have a lower mortality rate, although data are lacking to substantiate this claim.

Thus, from a management perspective, larger birds that reproduce slowly are much more difficult to reintroduce into the wild than are small-bodied raptors. For example, the California Condor is near extinction due to pesticides, poisoning, and illegal shooting. The birds have been brought into zoos and have been laying eggs there successfully. However, it takes a great deal of time and effort to produce a large enough population of birds so that they can be reintroduced into the wild. By the same token, it takes a long time for these birds to colonize new areas in the wild. It may take several years after introduction before a population begins to breed. There are no breeding adults for them to successfully imprint on, and there are many environmental factors that could cause them harm.

Reintroduction of the Peregrine Falcon, which has a more intermediate life span, has been accomplished by placing nestlings (hacking) throughout the eastern and western United States. By feeding at release sites, young falcons are able to imprint on these areas. In some cases, they return and nest there the following year. This process has begun to establish a wild population. Prairie Falcons have also been successfully reintroduced, but not to the same degree as Peregrines. In order to establish reintroduced populations, breeding must continue over a period of years, eventually resulting in a surplus of adult birds. This surplus then allows adults that are killed to be replaced quickly by available birds in the population. Thus, a population of more long-lived birds may be harder to destroy; however, when they are all harmed over a period of years by pesticide poisoning or shooting, the population is extremely difficult to replace.