Falco mexicanus

See Olsen et al. (1989) for a study of relationships within the genus Falco based on electrophoretic patterns of feather proteins.

Large range in western and central North America; mostly stable, with some local declines.

BREEDING: southeastern British Columbia, southern Alberta, southern Saskatchewan, and northern North Dakota south to Baja California, southern Arizona, southern New Mexico, western and northern Texas, Chihuahua, Coahuila, Durango, and San Luis Potosi (AOU 1983, Lanning and Hitchcock 1991, Steenhof 1998); formerly also northwestern Missouri. NON-BREEDING: from breeding range in southern Canada south to Baja California and central Mexico (AOU 1983, Steenhof 1998). Most abundant in winter in the Great Basin and the central and central-southern latitudes of the Great Plains (Root 1988).

HUMAN DISTURBANCE: The effect of direct human disturbance depends on a number of factors, including the type of activity, proximity to the nest or roost site, time of year and duration of the activity (Steenhof 1998). Falcons are most sensitive just prior to egg laying. In certain cases, disturbance has negative effects (Platt 1974, Boyce 1982) while in others, there appears to be no significant effect (Edwards 1968, Holthuijzen 1989). Birds also seem able to habituate to aircraft (Harmata et al. 1978, Ellis et al. 1991) and even simulated sonic booms (Ellis et al. 1991). However, large-scale and complex disturbances, such as military tank training, can disrupt foraging behavior and efficiency (Steenhof 1998). Prolonged disturbance is more harmful than periodic, short-term disturbance (Bednarz 1984). GRAZING: The effects of livestock grazing are neither simple nor well understood. The removal of vegetation may impact prey populations, especially in drought years (Steenhof 1998). Grazing also increases the invasion of sites by exotic invasive plants, such as cheatgrass (Bromus tectorum), which increase fire return intervals and accelerate the loss of native vegetation (Steenhof 1998, Wisdom et al. 2000). On the other hand, grazing removes vegetation which in some cases may make prey more available to falcons (Anderson and Squires 1997). However, this short-term, local benefit may be offset by negative effects at larger scales and in longer time frames. INVASIVE EXOTICS: In Idaho, home ranges had a lower cover of exotic annual grasses, primarily cheatgrass, than expected by chance (Marzluff et al. 1997). ENERGY DEVELOPMENT: Prairie Falcons appear to be relatively tolerant of oil and gas (Harmata 1991, Squires et al. 1993) and coal development (Phillips et al. 1990) in foraging areas, except where nest sites are destroyed or direct human disturbance is excessive. Falcons forage in spaces among oil wells where well densities were 1.5 wells per sq km (Anderson and Squires 1997). But the latter site was remote and not frequented by humans. This implies that it is direct human disturbance, not development per se, that is most harmful. RELATIONSHIPS WITH OTHER SPECIES: Falcons are notably tolerant of the Common Raven (Corvus corax) throughout its range (Cade, 1987, Steenhof 1998). Falcons frequently lay eggs in old raven stick nests. As raven populations and distribution are increasing, this may be a management factor deserving more attention. Golden Eagles (Aquila chrysaetos, Red-tailed Hawks (Buteo jamaicensis) and Great Horned Owls (Bubo virginianus) typically are not tolerated by falcons near nesting territories (Platt 1974, Harmata et al. 1978, Kaiser 1986, Holthuijzen 1989). These species prey on Prairie Falcon adults and nestlings. Peregrine Falcons often attack Prairie Falcons that enter a peregrine's territory (Porter and White 1973, Walton 1978). Thus, management actions to benefit these other raptor species may be detrimental to Prairie Falcon populations. SHOOTING: Shooting is the most commonly reported source of adult mortality (Webster 1944, Enderson 1964, van Tighem 1967). Shooting near nests also may cause adults to leave the nests temporarily, exposing eggs or nestlings to additional mortality (Harmata et al. 1978). PREDATORS: Mammalian predators, primarily coyotes (Canis latrans) and bobcats (Lynx rufus), are the main predators of falcon nests where nests are accessible (Steenhof 1998). DISEASE: Rock Doves (Columba livia) infected with trichomoniasis and herpesvirus can spread the infections to falcons when Rock Doves are consumed (Aini et al. 1993, Steenhof 1998). The impact of these diseases on falcon populations is not known. ELECTROCUTION: Electrocution is apparently uncommon (Steenhof 1998). FALCONRY: Legally harvested in 19 states (Conway et al. 1995). Although state agencies set harvest guidelines, these often are established without adequate data or analysis of population impacts. Steenhof (1998) states that the low level of harvest, about 0.2% of the population annually, probably does not affect overall population size. However, adults disturbed by harvest show lower inter-year territory fidelity (Conway et al. 1995). COLLISIONS: Collisions with wires, and fences in particular, cause some mortality, particularly during the fast, low foraging flights (Boyce 1982, Beauvais et al. 1992). Falcons also collide with vehicles. STOCK TANKS: Adults have been known to drown in stock watering tanks (Enderson 1964). ECTOPARASITES: Several ectoparasites contribute to nestling mortality and subsequent reproductive failure (review in Steenhof 1998). PESTICIDES: Susceptible to eggshell thinning from DDE (Noble and Elliot 1990) and may have had more recent reproductive failure as a result of hexachlorobenzene and DDE (Jarman et al. 1996). Although Prairie Falcons eat more mammals than birds, the species may be vulnerable to organophosphates and carbamates where it feeds on birds in agricultural areas (Kirk and Banasch 1996). Heptachlor epoxide and mercury residues also have been detected in falcons. These chemicals are used to treat wheat seeds and were presumable picked up by birds such as Horned Larks. Neither contaminant was thought to be high enough to affect the population level in the study area (Fyfe et al. 1969, 1976).