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Prairie Falcon
Falco mexicanus
Order
FALCONIFORMES
– Family
FALCONIDAE
Authors: Steenhof, Karen
Revisors: Steenhof, Karen

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Introduction

Adult male Prairie Falcon, Delle, UT, June.
Figure 1. Distribution of the Prairie Falcon.

This inhabitant of dry environments of western North America, where cliffs or bluffs punctuate open plains and shrub-steppe deserts, is an efficient and specialized predator of medium-sized desert mammals and birds, ranging widely in search of patchily distributed prey. Several species of ground squirrels (Spermophilus spp.) are the mainstay of the Prairie Falcon’s diet; they provide fat-rich calories that pairs need for raising their broods of 4–5 young during the 3- to 4-month nesting season. When ground squirrels move underground to escape summer heat and dryness, most Prairie Falcons leave their nesting areas in search of other prey. Horned Larks (Eremophila alpestris) and Western Meadowlarks (Sturnella neglecta) are important prey items in winter.

On its breeding areas, this falcon is often heard long before it is seen. Loud territorial and courtship calls are sometimes the only clue of its presence, because its nondistinct plumage blends in with the dark, earthy mineral colors of the cliffs on which it nests. The smaller male can be distinguished from the female by its more rapid wing-beats and shriller call. Prairie Falcons often share their nesting cliffs with Common Ravens (Corvus corax), Golden Eagles (Aquila chrysaetos), and Red-tailed Hawks (Buteo jamaicensis).

The hardy Prairie Falcon has always made its living in lands that are susceptible to periodic droughts. As a mammal-eating specialist, it survived the pesticide era better than the closely related, bird-eating Peregrine Falcon (Falco peregrinus). Now, as human populations expand into once unoccupied deserts, the Prairie Falcon persists in the face of agricultural encroachment, livestock-grazing, energy development, off-road vehicle use, and military training.

Most of our knowledge of this species comes from studies initiated to understand how humans influence nesting populations. During the 1970s, several studies (e.g., Fyfe et al. 1969, 1976, Enderson and Berger 1970, Leedy 1972, Enderson and Wrege 1973, Ogden and Hornocker 1977) assessed the impacts of organochlorine pesticides. More recent studies have focused on the effects of a variety of human activities, including mining (Becker and Ball 1981, Bednarz 1984), oil and gas development (Harmata 1991, Squires et al. 1993), recreation (Boyce 1982), agriculture (U.S. Dept. of Interior 1979), industrial construction (Holthuijzen 1989, Holthuijzen et al. 1990), harvesting for falconry (Conway et al. 1995), aircraft overflights (Ellis et al. 1991), and military training (U.S. Dept. of Interior 1996). The most extensive studies were undertaken at the Nelson Snake River Birds of Prey National Conservation Area (hereafter Snake River NCA) in sw. Idaho, where nesting densities are exceptionally high.

Reliable estimates of overall population size and trends are lacking for this species, especially in Mexico. Surveys should be conducted throughout its range, and more information is needed on the effects of habitat alteration on Prairie Falcon diet and breeding success, as well as on the availability of its prey.