The Prairie Falcon

Prairie FalconThe prairie falcon, known to ornithologists as the Falco mexicanus, is a medium-large falcon of western North America, the only larger falcon native exclusively to North America. It is an arid environment adaptation of the early peregrine falcon lineage, able to subsist on less food than the peregrine, and generally lighter in weight than a peregrine of similar wing span. Having evolved in a harsh desert environment with low prey density, the prairie falcon has developed into an aggressive and opportunistic hunter of a wide range of both mammal and bird prey. It will regularly take prey from the size of sparrows to approximately its own weight, and on occasion much larger.
It ranges from southern Canada, through the western United States, and into northern Mexico. The natural habitat of the prairie falcon is open and usually arid country. It breeds from south-central Canada through the western United States down to Baja California, Durango, and northern San Luis Potosí. It is much less migratory than the other North American falcons, but in winter it does withdraw somewhat from the northernmost and highest-elevation parts of its breeding range.
As of a decade ago, the population of prairie falcons was estimated to be stable or increasing at over 5,000 pairs, following some population loss due to the use of the pesticide DDT during the middle of the 20th Century. While DDT contamination extirpated the eastern U.S. peregrine falcon population in the 1950s and 1960s to as few as 350 pairs, it is believed the prairie falcon avoided the level of population loss suffered by the peregrine from DDT-induced egg shell thinning due to its more remote environment partly insulating it from pesticide contamination. The peregrine population loss allowed the expansion of prairie falcon range to cliff nesting sites in areas formerly occupied by peregrines moderately outside historic prairie falcon territory. The successful reintroduction of peregrines to the eastern and central United States brought peregrine and prairie falcons back into competition in these areas. The reintroduction program led by the Peregrine Fund bred and released more than 4,000 heavier-bodied peregrine falcons from 1974 to 1997, and the conflict over nesting sites resulted in the displacement of prairie falcons, which have returned to their natural range, as the prairie falcon with its greater heat tolerance, lower daily food requirement, and wider prey base has the survival advantage in the harsh desert environment in which it has evolved.
The prairie falcon outwardly resembles the peregrine as well as the Old World “hierofalcons,” but in recent decades genetic analysis has proven them to be distinct species. The prairie falcon is now considered an early aridland offshoot of the peregrine falcon lineage.
Moderately lower weight than the muscular peregrine for similar wingspan not only allows the prairie falcon to have lower food and energy requirements by the simple expedient of less muscle to support, but also allows a lighter wing loading (weight per square unit of wing area) that allows more distance to be covered per calorie consumed when hunting over prey-sparse terrain. The lighter wing loading also allows greater maneuverability, which is valuable in the pursuit of agile lightly wing loaded prey and rapidly dodging ground prey. When the prairie falcon locates needed prey, it is relentless in its pursuit.
Because they evolved in the harsh western environment, prairie falcons have developed the wherewithal to out-fly the strongest and quickest quarry within the longer-distance lower-prey-density environment of the American west. The prairie falcon evolved eyes that are proportionally larger relative to head size than the already large eyes of other falcons, giving it very keen vision and a further competitive advantage over the peregrine falcon in the desert.
Though they are separate species after several million years of mostly separate evolution, prairie falcons are known to still occasionally interbreed with peregrines in the wild. The male offspring of these crossings may be fertile, and provide an avenue for at least some gene flow to possibly still occur between the species. In keeping with the needs of a predator living in a prey-sparse desert environment, the prairie falcon has developed a wide range of hunting and flight styles. It often hunts by flying fast and low, at a height of ten to 12 feet, hoping to find surprised prey as it comes over the terrain or around bushes. Its cruising speed is estimated at 45 miles per hour and it accelerates in the chase. A variation on this method is for the falcon to descend from altitude and then level out near the ground, initially traveling at more than 100 miles per hour at altitudes of a roughly five feet, sometimes gliding for more than a half mile this way. If the rapidly approaching falcon flushes bird prey, the falcon has the speed advantage and may rapidly close with the prey. Another variation on these low attacks is using terrain as cover to approach beneath a flock of birds, then using its speed to perform a rapid climbing surprise attack into the flock. It also pursues prey sighted from a perch, again often flying low and using its speed to close with the prey in a tail-chase. Prairie falcons may even deliberately emulate the flight style of other birds in order to deceive potential prey and allow a surprise attack. Its high speed descent from high altitude allows it to overtake the swiftest of birds and to deliver a knock-out blow to large prey with a closed foot or feet, or a swipe with an open foot armed with talons. The claw on the hind toe, or hallux, is particularly effective and deadly in raking the prey.
Male prairie falcons are about 15 inches in length and weigh 1.1 to 1.4 pounds, on average. Females are about 17.7 inches in length and 1.7 to 2.1 pounds, on average. A large female can be nearly twice the size of a small male, with wingspan reaching to 3.5 feet, and tends to hunt significantly larger prey. Plumage is gray-brown (sometimes called “sandy”) above and pale with more or less dark mottling below. The darkest part of the upper side is the primary wing feathers; the lightest is the rump and tail, particularly the outer tail feathers.
This species nests on cliff ledges, so breeding adults are local during the breeding season. The clutch averages four eggs, which are subelliptical and pinkish with brown, reddish-brown, and purplish dots. As part of their adaptation to hotter and lower humidity desert climates, the eggs of the prairie falcon are less porous and retain water better than those of their peregrine falcon cousins, leading to a higher hatching rate under these conditions. The incubation period is 31 days, beginning with the second-to-last or last egg laid. Incubation becomes more intense after later eggs are laid, somewhat evening out hatching times. As is typical for falcons, the female does most of the incubating and brooding, and the male brings most of the food, with the female also hunting after the young are 12 to 14 days old. The young fledge from 36 to 41 days after hatching. They continue to be supported by their parents while learning to fly and hunt, with the parents gradually winding down the amount of food they provide as the youngsters’ hunting skills improve. At approximately 65 days of age they are ready to be self-sufficient, and disperse from their natal area
Juveniles resemble adults except that they have dark streaks on the breast and belly and darker, less grayish upperparts.
Calls, heard mostly near the nest, are described as repetitive kree kree kree…, kik kik kik…, and the like, similar to the peregrine’s but higher-pitched.
Prairie Falcons sometimes bathe in river shallows, but dust-bathing is probably more common than water-bathing, because of the general scarcity of standing water in its habitat
The prairie falcon eats mostly small mammals and small to medium-sized birds caught in flight, though as an opportunistic predator it will occasionally take larger birds which may be up to five times its weight. It usually takes prey smaller than itself that it may safely subdue and which can be carried to the nest or to a safe perch to consume. The majority of prey is six ounces or less, a weight that even the smaller male can carry long distances back to the nest. Most prey is thus 30 percent less of the weight of the male. Common mammalian prey for prairie falcons includes squirrels, ground squirrels, prairie dogs, chipmunks, gophers, and rabbits of various species. Reptiles are also sometimes taken. Bird prey commonly includes sparrows, starlings, grackles, doves, quail, meadow larks, pigeons, coots, teal, and mallards—virtually any bird of up to approximately the falcon’s own size and occasionally significantly larger. However, the need to feed their young focuses them on prey they can carry during nesting season, and the reproductive success of the prairie falcon depends upon such smaller prey being available.
From Wikipedia and 14 Interesting Facts About The Prairie Falcon.

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