The Peregrine Falcon (Falco peregrinus) is a raptor celebrated for its incredible speed, capable of reaching over 200 miles per hour during its hunting dive, known as a stoop. This agility has allowed the falcon to colonize nearly every continent, making it one of the most widely distributed bird species in the world. As a bird of prey that feeds almost exclusively on other birds, the Peregrine Falcon occupies a high position in the food chain. Due to their aerial mastery, healthy, free-flying adults have very few natural enemies.
Predators of Eggs and Nestlings
The most frequent and successful predation on Peregrine Falcons occurs when the birds are unable to defend themselves or escape, primarily at the nest site. Eggs and newly hatched chicks, or nestlings, are vulnerable targets for opportunistic animals. Terrestrial mammals like raccoons, martens, and foxes can raid nests situated in accessible locations, particularly those not on sheer cliff faces or tall buildings.
Larger avian predators also pose a threat to young falcons and their eggs. Great Horned Owls, eagles, and large gulls are known nest raiders that will take young birds. Adult falcons are fiercely territorial and will aggressively attack intruders to defend their young, but they cannot always deter a determined predator. The high mortality rate for young falcons, which can be up to 70% in their first year, is largely attributable to this early-life predation.
Predators of Juvenile and Adult Falcons
Once a Peregrine Falcon leaves the nest and develops its flying skills, the list of animals capable of preying on it shrinks dramatically. The primary natural threat to a healthy juvenile or adult falcon comes from larger raptors. Golden Eagles and Gyrfalcons possess the size and strength to overpower an adult Peregrine Falcon, though these predatory interactions are uncommon.
The Great Horned Owl (Bubo virginianus) is considered a significant predator of adult falcons because it hunts nocturnally. Falcons are diurnal, meaning they are active during the day, making them vulnerable to ambush while roosting at night. Peregrine Falcons may also occasionally be killed by other Peregrines during territorial disputes, which can result in fatal combat.
Significant Causes of Non-Predatory Mortality
While predation is a natural factor, the leading causes of death for adult Peregrine Falcons are often non-predatory and related to human environments. Collisions with human-made structures are a major mortality factor, especially in urban areas where falcons hunt and nest on skyscrapers. Accidents involve striking buildings, power lines, or vehicles during high-speed flight.
Historically, the widespread use of the pesticide DDT caused a catastrophic decline in falcon populations. As an apex predator, the falcon accumulated high concentrations of the chemical, leading to eggshell thinning and reproductive failure. Although DDT has been banned, modern falcons still face risks from other environmental contaminants and diseases like Aspergillosis.