Arizona supports one of the densest peregrine falcon populations in the contiguous United States, thanks to an abundance of sheer cliff faces, deep canyons, and a year-round supply of avian prey. From the towering walls of the Grand Canyon to the desert bluffs near Phoenix and Tucson, peregrines have carved out a remarkably successful existence in a landscape that, at first glance, seems better suited to rattlesnakes than the world’s fastest bird. Their story in Arizona involves a dramatic crash during the DDT era, a hard-fought recovery, and a hunting ecology shaped by the state’s stark regional differences in terrain and prey availability.
Cliff Country and Canyon Walls
Peregrines are cliff nesters by nature, and Arizona delivers cliffs on an almost absurd scale. The Grand Canyon alone offers hundreds of miles of vertical and near-vertical sandstone and limestone faces, many of them inaccessible to ground predators and human disturbance. The Colorado River corridor, stretching from the canyon downstream through a chain of large reservoirs, provides additional nesting habitat on dam faces, bridge abutments, and the natural rock walls that line the river’s path through the desert. Beyond these marquee landscapes, peregrines nest on smaller cliff bands across central and southeastern Arizona, including the Mogollon Rim, the mountains near Prescott, and the sky islands of the southeast.
What makes Arizona particularly attractive is the combination of vertical rock and nearby foraging habitat. Peregrines do not hunt far from their nests during the breeding season, so a cliff ledge overlooking a river, lake, or riparian corridor is ideal. The reservoirs along the lower Colorado River concentrate waterfowl, shorebirds, and other waterbirds in a narrow corridor through otherwise arid land, creating a reliable prey base at the foot of suitable nesting cliffs. That pairing of nesting substrate and prey concentration is a big part of why Arizona’s peregrine density has remained high even as the species has shifted and fluctuated elsewhere in the West.
What Arizona Peregrines Eat
One of the more striking things about peregrine falcons in Arizona is how much their diet shifts depending on where in the state you look. A long-term study spanning 25 territories and over a decade of data collection found clear regional patterns. In northern Arizona, peregrines relied heavily on White-throated Swifts and birds passing through on migration. In central and southeastern Arizona, the average prey item was heavier, and doves and pigeons made up the largest share of the diet.
The overall prey list is staggering. Across the state, researchers documented over 100 avian prey species taken by peregrines, along with small numbers of mammals and insects. Using statistical modeling to account for prey remains that were missed or degraded, the estimated total number of bird species taken ranged from about 86 in southeastern Arizona to over 110 in both the northern and central parts of the state.
Along the Colorado River through the Grand Canyon, the diet picture is even more varied. A detailed foraging study there recorded peregrines attempting to catch at least 44 species, including more than 40 kinds of birds. The breakdown of prey types tells a vivid story of opportunism:
- Swifts and swallows: about 29% of foraging attempts
- Waterfowl: roughly 27%
- Other waterbirds: around 11%
- Bats: about 10%
- Large wasps: roughly 8%
- Other species: about 15%
Bats as a tenth of the diet is a detail that surprises most people, but along the canyon’s river corridor, bats emerge in large numbers at dusk and dawn, and peregrines are skilled enough to snatch them from the air. Their success rate on bats was remarkably high at 87%, second only to large wasps at 100%. Success on waterfowl and swifts was lower, around 40-42%, and small shorebirds proved nearly impossible to catch, with a success rate below 3%.
Hunting Techniques in the Canyons
The Grand Canyon and similar deep-walled terrain give Arizona peregrines a vertical playground that few other populations in the country can match. The classic peregrine stoop, a high-speed dive onto prey from above, becomes especially dramatic when a falcon launches from a canyon rim a thousand feet above the river. Researchers have described long series of declining stoops on White-throated Swifts that involved elevation changes of up to a kilometer, with the falcon diving repeatedly on the swift flock as both predator and prey spiraled downward through the canyon.
These repeated stoops sometimes shift into something more acrobatic. Instead of only striking while diving, falcons occasionally attempt to grab swifts while climbing back upward after a missed stoop. A less flashy but effective technique involves a peregrine swooping up near a cliff face, stalling in the air, and grabbing at swifts as they dart in and out of crevices in the rock. Swifts roost and nest in narrow cliff cracks, and a peregrine that learns the location of an active roost can intercept birds at close range without the energy cost of a long aerial chase.
Across the broader dataset from the Colorado River, air-to-air strikes dominated overwhelmingly, accounting for 94% of observed foraging attempts. Air-to-water strikes, typically on ducks or grebes sitting on the river surface, made up about 4%, and air-to-ground strikes were rare at around 2%. The canyon environment funnels both prey and predator into a narrow vertical space, which likely amplifies the aerial hunting style that peregrines already prefer.
Breeding Success Along the Colorado River
Arizona’s peregrine population is not just large; it is productive. A multi-year study of breeding pairs associated with reservoirs on the Colorado River tracked 117 nesting attempts and documented at least 197 young reaching the age of about four weeks. Annual breeding success ranged from 64% to 82% and averaged just over 72%, with no significant variation from year to year during the study period. That kind of consistency suggests a stable population with reliable food and relatively low disturbance at nest sites.
Reproductive output averaged 1.8 young per nesting attempt when counting all pairs, including those that failed. Among successful pairs only, the average rose to 2.4 young per nest. These numbers are solid by peregrine standards. A pair that consistently fledges two or more young per year is replacing itself and then some, which is what a healthy, growing or stable population looks like.
The reservoir environment along the lower Colorado deserves some credit here. Reservoirs concentrate prey year-round, buffering against the seasonal fluctuations in food availability that can suppress breeding success in more remote or arid territories. Cliff faces near dam structures and reservoir shorelines also tend to be relatively protected from mammalian predators like raccoons or ringtails that can raid peregrine nests in more accessible terrain.
The DDT Crash and Recovery
Arizona’s current peregrine abundance makes it easy to forget how close the species came to disappearing from the state entirely. Like peregrine populations across North America, Arizona’s birds were devastated by the pesticide DDT and its breakdown product DDE during the mid-twentieth century. DDE accumulated in the food chain, concentrating in the bodies of the small birds that peregrines eat, and caused peregrine eggshells to thin so severely that eggs broke under the weight of incubating adults.
A study of organochlorine contamination in peregrine prey across eight western states, including Arizona, found that DDE accounted for 72% of total organochlorine concentrations in the small birds sampled. Prey from 13 species contained DDE levels above the threshold considered sufficient to inhibit normal reproduction in the raptors feeding on them. The researchers concluded that harmful organochlorine concentrations were present in certain western migratory birds and posed an even greater hazard to avian predators like the peregrine falcon.
After DDT was banned in the United States in 1972, peregrine populations began a slow recovery aided by captive breeding and reintroduction programs. Arizona was one of the success stories. The state’s extensive cliff habitat meant that as contamination levels dropped, reintroduced and naturally dispersing birds had no shortage of places to set up territories. By the time the peregrine falcon was removed from the federal endangered species list in 1999, Arizona already supported a robust breeding population, and numbers have continued to grow or hold steady since then.
The residual concern with organochlorines has not vanished entirely. DDE is persistent in the environment, and migratory prey birds that winter in Latin America, where some organochlorines remained in use longer than in the U.S., can still carry detectable levels. But the concentrations have dropped enough that reproductive impacts are no longer a population-level problem for Arizona peregrines.
Coping with Desert Heat
Hunting birds on the wing in triple-digit desert heat seems like a recipe for overheating, and the question of how peregrines manage it is a fair one. Research comparing the peregrine to the Grey Falcon, an Australian species that inhabits some of the hottest arid landscapes on Earth, offers an interesting contrast. The Grey Falcon was found to have no special physiological or body-structure advantages for handling heat compared to other birds. Instead, it relies almost entirely on behavioral adaptations: keeping activity levels and physical exertion as low as possible throughout its life. That strategy minimizes internal heat production and makes thermoregulation easier when the air temperature is extreme.
The peregrine, by contrast, is a high-effort hunter. Its signature tactic involves fast, energy-intensive aerial pursuit and high-speed stoops. The researchers specifically noted that the peregrine’s active hunting style contrasts strikingly with the Grey Falcon’s low-activity approach. So how do Arizona peregrines get away with it?
Part of the answer is timing. Arizona peregrines shift their hunting activity toward the cooler hours of the day during summer, concentrating effort in early morning and late evening. The Grand Canyon’s microclimate also helps: temperatures at the river level can be significantly different from those on the exposed rim, and canyon walls provide shade for much of the day. Peregrines nesting on north-facing cliff ledges or in shaded alcoves avoid the worst of direct solar radiation during incubation and brooding, which is a meaningful advantage when ambient air temperatures climb above 40°C.
Water availability along the Colorado River and its reservoirs is another factor. Unlike peregrines nesting on isolated desert cliffs far from water, those in the river corridor have access to drinking water and the evaporative cooling that comes with proximity to a large water body. The humid air rising off the river is a small but real thermal buffer that an arid inland cliff would lack entirely.
Regional Differences Across Arizona
Arizona is not one habitat but many, and peregrine ecology varies accordingly. The northern part of the state, dominated by the Colorado Plateau with its deep canyons and pinyon-juniper woodlands, produces a peregrine diet heavy on swifts and migratory songbirds. White-throated Swifts are especially important prey in this zone, which makes sense given that swifts are abundant around the same cliff faces where peregrines nest.
Central Arizona, including the area around the Verde River and Mogollon Rim, supports a somewhat different prey community. The diet here is broader in terms of average prey size, and doves and pigeons play a larger role. Mourning Doves, White-winged Doves, and Rock Pigeons are all common in central Arizona’s mix of desert, riparian, and semi-urban landscapes, and they are heavy enough to provide a substantial meal for a peregrine or its nestlings.
Southeastern Arizona, with its sky island mountain ranges and grasslands, has the narrowest estimated prey diversity of the three regions, at roughly 86 species compared to over 110 in the north and central zones. But what it lacks in variety it makes up in prey mass. The columbiforms, doves and pigeons, again dominate the diet here, and the overall average weight of prey items is higher than in the north. For a breeding pair trying to fuel the rapid growth of two or three nestlings, heavier prey means fewer hunting trips per day, which is a real efficiency gain.
These regional dietary shifts reflect the broader biogeography of Arizona. The north is a corridor for neotropical migrants heading between Mexico and breeding grounds farther north, so peregrines there benefit from seasonal pulses of songbirds passing through. The south and center have more resident bird communities anchored by year-round species like doves, quail, and thrashers. Peregrines are flexible enough to exploit whatever is locally abundant, which is part of why they have succeeded across such a geographically diverse state.
Urban Peregrines in Arizona
Peregrine falcons have taken to cities across the United States, and Arizona is no exception. Tall buildings in Phoenix and Tucson mimic the cliff ledges that peregrines naturally seek for nesting, and the urban pigeon and dove populations provide a concentrated, year-round food supply. Several pairs are known to nest on high-rise buildings, bridges, and other structures in the Phoenix metropolitan area, and birders in downtown Tucson have documented peregrines hunting from rooftops.
Urban nesting comes with its own set of risks. Window collisions are a leading cause of injury for young peregrines learning to fly in a cityscape, and artificial lighting can disorient fledglings during their first flights. Vehicle strikes, electrocution on power infrastructure, and poisoning from rodenticides consumed by prey species are additional hazards that wild cliff-nesting peregrines rarely face. Despite these threats, urban pairs in Arizona have successfully fledged young in multiple years, suggesting that the food supply and nest-site security of tall buildings offset some of the novel dangers.
The presence of urban peregrines also creates opportunities for public engagement that wildland populations cannot. Nest cameras installed on buildings in several Arizona cities have given tens of thousands of viewers a front-row seat to peregrine breeding, from egg-laying through fledging. These cameras have been particularly effective at building public support for raptor conservation in a state where much of the population lives far from the remote canyons where most peregrines breed.
Lingering Threats and Ongoing Monitoring
Arizona’s peregrine population is in good shape overall, but it is not free of concerns. Climate change is altering the timing of prey migration and the intensity of summer heat, both of which could affect breeding success over the coming decades. Drought years reduce riparian habitat along rivers and streams, pushing prey species away from traditional peregrine nesting areas and potentially forcing birds to forage over longer distances.
Recreational activity in canyon country has also increased substantially. Rock climbing, river rafting, and helicopter tours bring human presence close to nest sites during the breeding season. Peregrines are more tolerant of disturbance than some raptors, but repeated close approaches during egg incubation or early brooding can cause nest abandonment, particularly among younger, less experienced pairs. Seasonal closures of climbing routes near known peregrine eyries are in effect at several sites in the Grand Canyon and on national forest land, though enforcement is inconsistent.
Lead exposure is another issue that has received growing attention. Peregrines occasionally scavenge on waterfowl or upland game birds that carry lead shot or bullet fragments, and even low-level lead ingestion can impair neurological function and reproductive output. The shift toward non-toxic ammunition on some public lands in Arizona has helped, but lead remains present in the environment at levels that warrant continued monitoring. State and federal wildlife agencies continue to survey peregrine nest sites across Arizona annually, tracking occupancy rates, breeding success, and contaminant levels to catch any emerging problems before they become population-level crises.