Why Do Peregrine Falcons Live in Cities? Skyscraper Nests

Buildings are artificial cliffs

In the wild, the peregrine falcon nests on high cliff ledges, usually under an overhang, with a wide view and open air below for hunting. It builds no nest, simply scraping a shallow hollow in gravel or soil.

A skyscraper, cathedral spire, bridge tower or power station chimney offers almost exactly the same things: a high, sheltered ledge that ground predators cannot reach, a lookout over open space and plenty of updrafts for soaring. To a peregrine, the stone and concrete canyons of a city are simply a new kind of cliff. In the UK, the first recorded urban pair was found on Swansea’s Guildhall in the 1980s, and city nesting has since spread widely, especially in southern England, where natural inland cliffs are scarce.

Cities are full of pigeons

The second reason is food. Cities hold huge numbers of feral pigeons, the domestic descendants of the rock pigeon, which itself originally nested on sea cliffs. Pigeons are the right size for a peregrine, fly in the open between rooftops and are available all year round.

Studies of prey remains show that feral pigeons can make up 80% or more of an urban peregrine’s diet. City falcons also catch starlings, collared and mourning doves, blackbirds, robins, swifts, gulls, crows and jays. Our article what do peregrine falcons eat? explains how they catch them.

Artificial light gives city falcons an extra advantage. Floodlit buildings let peregrines keep hunting after dusk, and in the UK and elsewhere urban peregrines have been seen catching night-migrating birds such as redwings, woodcocks, quail and rails as they pass over brightly lit city centers.

From the DDT crash to city skylines

Peregrines occasionally nested on buildings in the past. One famous female raised young on a ledge of the Sun Life Building in Montreal from 1936 to 1952. But urban peregrines only became common after the species collapsed in the mid-20th century and then recovered.

In the 1950s–1970s, the pesticide DDT caused peregrines to lay thin-shelled eggs, and the species disappeared as a breeding bird from the eastern United States and parts of Europe. When recovery programs began, falconers and biologists released captive-bred young from “hack boxes” on towers and tall buildings, as well as on cliffs. City release sites often had a useful advantage: fewer great horned owls, the main predator of young peregrines on many natural cliffs.

Many released falcons, and their offspring, chose buildings and bridges as nest sites, and the habit spread. In 1978 a female known as Scarlett settled on an office tower in downtown Baltimore, one of the first well-known urban peregrines of the recovery era. Today urban peregrines breed in hundreds of cities across North America, Europe and Australia.

Famous city nests and webcams

Urban peregrines are now some of the most watched wild birds in the world, thanks to nest cameras and public viewing points. Some well-known examples include:

• New York City, with a few dozen pairs nesting on bridges, church towers and high-rise buildings.
• London, where peregrines nest on landmarks along the Thames and RSPB volunteers have run public viewing at Tate Modern.
• Derby Cathedral in England, whose nest platform and webcams have followed peregrine families since 2006.
• Norwich, Worcester and Nottingham in England, all with cathedral or university nest cameras.
• Melbourne, Australia, where peregrines have nested for decades on an office tower on Collins Street.
• Chicago, which made the peregrine its official city bird.

In some places the birds have become a substantial share of the regional population. Portland, Oregon, for example, holds about a tenth of all the peregrine nests in the state despite covering a tiny fraction of its area.

How people help city peregrines

Because a bare roof ledge can be smooth and exposed, eggs may roll away or sit in rainwater. Many building owners and conservation groups install nest trays or boxes: shallow trays filled with gravel, placed on a sheltered ledge, that give the falcons a safe scrape.

Protection matters too. In the UK, peregrines are specially protected while nesting. In 2013, engineers sent to repair a faulty phone mast in Southampton found a peregrine nest on it and had to wait until the chicks fledged before finishing the work. In some cities, volunteers run “fledge watches” in early summer, keeping an eye on young falcons that land on streets or rooftops on their first clumsy flights.

Dangers of city life

City living is not risk-free for peregrines. Young birds can crash into windows or end up stranded at street level when they first leave the nest. Some urban falcons pick up poisons from pigeons that have eaten bait, or build up heavy metals and other pollutants from their prey. Collisions with wires, vehicles and glass are common causes of death. Even so, urban populations have grown steadily, showing how well this cliff-dwelling hunter has adapted to life among skyscrapers. For more on what makes it such a formidable hunter, see how fast can a peregrine falcon fly?.