If You Build It, They Will Come: Better Design Can Turn Cities into Urban Ecosystems


The recovery of the peregrine falcon is an environmental success story. Before the EPA banned DDT in 1972, peregrine falcons populations had plummeted, with as few as 40 pairs nesting around the Great Lakes. By 2015, 224 peregrine falcon pairs were breeding in Great Lakes states and Ontario.

The falcon’s restoration is largely attributed to the EPA’s 1972 DDT ban, but another factor helped support the falcon’s resurgence: skyscrapers.

Buildings taller than 500 feet have sprouted in Chicago since the 1960s. Source:

The proliferation of skyscrapers and tall buildings has played a major role in helping peregrine falcons thrive in the Great Lakes, creating new nesting habitat in urban spaces. In the “natural” environment, peregrine falcons tend to nest in scrapes and cliffs edges, of which there are relatively few in the Great Lakes area compared to, say, the Rockies of the Pacific Northwest. Similar “unnatural” manmade structures, particularly skyscrapers and bridges, started springing up in American cities like Chicago in great numbers by the 1960s, and featured designs that inadvertently accommodated falcon nests. In 1988, a narrow ledge on the 34th floor of a building in downtown Chicago became the nesting site for the the first two peregrine chicks born in Illinois since 1951. Today, 20 out of 29 falcon nesting territories in Illinois are located on buildings within the city of Chicago. Though the early sites were unplanned, creating nesting sites is now as simple as building a nest box, using the publicly available design and guide from the Raptor Resource Project.


Several nests have live streams from April to July, and one pair and their four chicks even gained Instagram-fame when a Lakeview resident documented their life on his 28th-floor - and because peregrine falcons mate for life and return to their nesting site, @officebuddha welcomes his friends home each spring.

New urban forms, like skyscrapers, can help develop new kinds of ecological “niches,” helping once rare populations to become established in new places. Whereas peregrine falcons have thrived in our new urban landscapes by accident, we can now design our cities and buildings in such a way as to help wildlife thrive. For example, 1.5 million Mexican free-tailed bats have made the Congress Avenue Bridge in Austin, Texas, their home, attracting thousands of people every year to witness them emerge to flock and feed at night. The experience led Texas to adapt bridges across the state to maximize use by bats, and 218 structures are currently used as roosts throughout Texas. Some towns even commission new edifices with wildlife specifically in mind: a town in the Netherlands built a bridge for pedestrians, cyclists… and bats.

Concrete slats enclose three types of habitat for bats to roost in spring, summer and winter, on the Vlotwatering bridge in Monster, Netherlands. Photo credit: Raymond Rutting / NEXT Architects.

Mass urbanization and suburban sprawl can have disastrous impacts on wildlife, tearing down and paving over valuable habitat. But intelligently designed “manmade” spaces can offer other forms of habitat. Urban areas may be recolonized by species that adapt to urban spaces, allowing us to now speak of “urban biodiversity” that goes far beyond pigeons, ants and street trees.

Repurposing balconies and bridges is part of a wider movement of “biophilic design,” which integrates nature and natural materials and forms into architecture and design to renature human spaces and restore our connection to nature, severed by urban living. Natural features for urban spaces can exist in many forms, from the streets to the roofs, including green roofs and facades, bioswales, or building shapes that mimic biological designs. Many of these features also seek to maximize the benefits of natural environments for people, cooling down street to combat the urban heat island effect, ventilating spaces for more comfort, capturing and filtering polluted rainwater, offering urban agriculture opportunities, or simply allowing people to enjoy, relax, and play in green spaces.

Cities may be manmade, but better urban design can support and enhance biodiversity, including rare or endangered species like peregrine falcons and bats, and improve management of the urban environment as a whole. Far from the deserts we think them to be, cities are where resilient and adaptable species interact with intelligent urban design, people and one another - the textbook definition of an ecosystem. Beyond maximizing services rendered by urban biodiversity, biophilic design is a way for us to restate our place within the natural environment and create new opportunities for man and nature to thrive in shared spaces.