Peregrine falcons nest on high, steep cliff ledges, and increasingly on tall buildings and bridges in cities, where they lay 3–4 eggs in a simple scrape without adding nesting material. These raptors do not build traditional nests; instead, the female scrapes a shallow depression in loose substrate like gravel, dirt, or sand on a sheltered ledge.
Natural Nesting Habitat
Historically, peregrine falcons nested on remote cliff faces, often near water where prey like ducks and shorebirds are abundant. They favor ledges with a vertical drop below, an overhang above for protection from weather and predators, and a clear flight path to the entrance. In mountainous regions, they may use the same cliff for generations, with each pair defending a territory of several square miles.
Unlike many birds, peregrines do not add twigs, grass, or feathers to the nest. The female simply scrapes a shallow bowl into the substrate, which helps keep the eggs from rolling off the ledge. This behavior is shared with other falcons and is known as a scrape nest.
Urban Nesting on Buildings and Bridges
Since the mid-20th century, peregrine falcons have adapted to urban environments, nesting on skyscrapers, water towers, and suspension bridges. These structures mimic the vertical cliffs of their natural habitat, and cities often provide abundant prey such as pigeons and starlings. Many cities now install nest boxes on ledges or towers to encourage breeding, and some maintain webcams to monitor the birds.
Urban nests are typically on high ledges, window sills, or under bridge decks. The birds show strong site fidelity, often returning to the same building year after year. One famous example is the pair that nested on the SunTrust Building in Richmond, Virginia, in the 1990s, which helped spark a wave of urban peregrine monitoring across the eastern United States.
Egg Laying and Incubation
Peregrines typically lay eggs in late March or April in the Northern Hemisphere, though timing varies with latitude. The female lays one egg every 1–2 days, with a clutch of 3–4 eggs being most common. The eggs are creamy white to buff with reddish-brown blotches, and each weighs about 40–50 grams.
Incubation lasts about 29–33 days, with the female doing most of the incubation while the male brings food. The male may briefly incubate while the female eats. The eggs hatch asynchronously, meaning the first chick may emerge a day or two before the last, leading to size differences among siblings.
Raising the Chicks
Peregrine chicks, called eyases, are covered in white down and are helpless for the first few weeks. The female broods them constantly for the first 10–14 days, while the male hunts and delivers prey to the nest. The female tears food into small pieces and feeds the chicks directly.
After about 3–4 weeks, the chicks are large enough to be left alone while both parents hunt. They begin to exercise their wings, a behavior called fledging, at around 35–42 days. After fledging, the young stay near the nest for another 2–3 weeks, learning to fly and hunt from their parents. They become independent at about 6–8 weeks after hatching.
Nest Site Selection and Territory
Peregrine falcons are highly territorial during the breeding season. A pair will defend a nesting territory of roughly 1–3 square miles, though this varies with prey availability. They often use the same nest site for many years, and if one member of a pair dies, the surviving bird will usually find a new mate and continue using the same ledge.
Nest site selection is influenced by several factors, including:
- Height and inaccessibility to ground predators
- Proximity to water or open areas with abundant prey
- Presence of a sheltered overhang or recess
- Lack of human disturbance (though urban birds tolerate more)
In some regions, peregrines have also nested on artificial platforms erected specifically for them, such as on power pylons or in quarries.
Common Problems and Conservation
Peregrine falcons faced a severe population decline in the mid-20th century due to the pesticide DDT, which caused eggshell thinning and breakage. By the 1970s, they were extirpated from the eastern United States and many parts of Europe. Conservation efforts, including captive breeding and release programs, helped populations recover, and the species was removed from the U.S. Endangered Species List in 1999.
Today, common threats to nesting peregrines include:
- Human disturbance at nest sites, especially during early incubation
- Collisions with buildings and windows
- Predation by great horned owls, raccoons, and other animals
- Pesticide contamination in some regions
Many cities and conservation groups monitor nests and protect them during the breeding season, sometimes closing ledges or erecting barriers to prevent disturbance.
Frequently Asked Questions
Do peregrine falcons use the same nest every year?
Yes, peregrine falcons are highly faithful to their nest sites. A pair may use the same cliff ledge or building ledge for many years, often for their entire lives. If one bird dies, the new mate will usually continue using the same site.
How long do peregrine chicks stay in the nest?
Peregrine chicks fledge (leave the nest) at about 35–42 days after hatching. However, they remain near the nest for another 2–3 weeks, depending on their parents for food and learning to hunt. They become fully independent at about 6–8 weeks old.
What do peregrine falcons eat during nesting?
Peregrine falcons eat mostly other birds, which they catch in mid-air. Common prey includes pigeons, doves, ducks, shorebirds, and songbirds. During nesting, the male does most of the hunting and brings food to the female and chicks. They may also eat small mammals and occasionally insects.
Are peregrine falcons aggressive to humans near their nests?
Peregrine falcons can be very defensive of their nest, especially when chicks are present. They may dive-bomb or strike intruders, including humans, with their talons. This behavior is most intense within a few dozen meters of the nest. It is best to observe from a distance and avoid approaching active nests.
Why do peregrine falcons nest on buildings?
Tall buildings and bridges resemble the cliff faces that peregrines naturally use, offering high ledges with a clear view and protection from ground predators. Cities also provide abundant prey, such as pigeons and starlings, and often have fewer natural predators. This adaptation has helped the species recover in urban areas.
Conclusion
Peregrine falcon nesting is a remarkable example of adaptability, from remote cliffs to bustling city skyscrapers. Their simple scrape nests, dedicated parental care, and strong site fidelity have allowed them to thrive in a changing world. Whether you spot a nest on a cliff or a downtown building, understanding their habits enriches any sighting.
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