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n 2008 I was working as a land steward at a local land conser-

vancy called the Pennypack Ecological Restoration Trust, attending

graduate school at the University of Pennsylvania, and living in South Philly

near the Italian market. I was constantly mindful of an incongruous juxtaposition

in my life: I studied and worked toward the restoration of native ecosystems by day, and I

returned each night to live in the mass of urban concrete and asphalt humanity that is Philadelphia.

Fittingly, I became interested in a suite of bird species that have adapted to life in this anthropogenic

terrain around me. I have found that their life stories are complex and intertwined, reflecting both the

twists and turns of fate and the guiding principles of evolutionary biology.

Nightlife in the Big City

Michae l Co l l • Media , Pennsy lvan ia • mco l l@nat lands .org

The UrbanNaturalHistory ofthe CommonNighthawk

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Nighthawks: Homage. Acrylic on wood by © Ray Nelson.

Discuss your reaction to Ray Nelson’s homage to EdwardHopper’s famous 1942 painting, Nighthawks: aba.org/birding

For many of us, the urban avifauna is represented by suchspecies as the Rock Pigeon, Eurasian Collared-Dove, Eu-

ropean Starling, House Finch, and House Sparrow. In muchof their urban ranges, they are exotics—introduced long agofor their aesthetic value, but today regarded as pests. Theyclog drains and eaves with their nests, they are alleged tospread disease, and they are noisy and conspicuous.

But there’s a lot more to the urban avifauna than thesehighly successful exotics.

Peregrine Falcon numbers, for example, have increasedsharply in response to population restoration efforts inPhiladelphia and other major American cities. Peregrineshave been deliberately placed on bridges in many urbanareas because these structures replicate both the shape andthe protection offered by the falcons’ natural nesting loca-tions on cliff edges. Peregrines have thrived in this artificial

environment. Here the young are largely free from preda-tion by owls, and the habitat is rich with prey in the form ofnaive urban birds. In their new niche, Peregrine populationshave recovered from near-extinction, due to the use of DDT,in the mid-20th century. According to a June 2013 report bythe Pennsylvania Game Commission,  there are nearly asmany urban-nesting Peregrines in Pennsylvania alone aswere present in all U.S. cities in the early 1980s.

Aerial insectivores are another group of birds that havecarved out a piece of the urban ecosystem. The ChimneySwift, like its slightly larger European counterpart the Com-mon Swift, has moved from tree cavities and cliffs to hollowsin buildings and chimneys. Chimney Swifts now nest almostexclusively in manmade structures, a fact that is likely con-tributing to recent declines in their numbers. Modern chim-ney designs are less suitable for nesting and more likely to be

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The appreciation of urban wildlife is an emerging and undeniable focus for birdersin the 21st century. From non-native sparrows and starlings to high-flying falconsand nighthawks, hundreds of bird species have adapted to city living in the ABAArea and beyond. West Kensington, Philadelphia. Photo by © Justin Wolfe.

covered by a guard. (See Paul Hess’s summary in the July 2011Birding, p. 27, for more on Chimney Swift declines.)

But it is the life story of another aerial insectivore that cap-tured my interest when I lived in Philadelphia. In the city,streetlights stay on all night, their high-pressure sodium lampsgiving off an amber glow that mixes with the smoggy sky tocreate a ubiquitous orange haze. Many nights I would sit onthe stoop outside my apartment and, though I couldn’t see itthrough the haze, I would hear the call of a CommonNighthawk displaying above me. Away from large human pop-ulation centers, nighthawks are chiefly crepuscular hunters.In the city, however, ample ambient light allows for visual lo-cation of insects and hunting right through the night.

As with the urbanization of Peregrine Falcons, I was struckby this improbable integration of human systems and struc-tures with the life history of the nighthawk. This was not justsome House Sparrow making a home beneath an awning; thiswas a nightjar that catches insects on the wing, nests on bareground, and migrates thousands of miles to another hemi-

sphere each winter. Yet there it was, performing aerial matingdisplays and living on a rooftop in the middle of the city, some-where on my block.

Like the Chimney Swift, the Common Nighthawk in east-ern North America has a life story that includes being dis-placed from its original habitat, prospering in a new emerginghabitat in the form of human dwellings, and ultimately be-coming vulnerable as a species because of its learned de-pendence on an ephemeral form of architecture. Of course,we need to study population trends and the species’ behavior.But we also need to implement conservation actions, and akey initiative will be to re-create the artificial habitats thesebirds learned to utilize in the 19th century. It is my hope thatthe relationship between humans and these elegant creatures,however precarious, can persist.

Population DeclineThe Common Nighthawk has experienced drastic declinesthroughout its range in North America, especially in the past

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20 years. Results of the Breeding Bird Survey (BBS) show anannual decrease of 2.7% survey-wide since 1980. The rateof this decline is highest in the Eastern BBS Region (–5.6%per year) and in Canada (–5.4%).

Pennsylvania is one of many states reporting substantialcontractions in the breeding range of the CommonNighthawk. Only 217 of more than 4,000 blocks in the sec-ond Pennsylvania Breeding Bird Atlas (2004–2008) reportedthe presence of nighthawks, yet 754 blocks had nighthawksin the first Pennsylvania atlas, 20 years earlier.

Because of their crepuscular and nocturnal ways,nighthawks often do not appear in many daytime birdcounts. The inconsistency of resulting abundance reportsmakes understanding trends in nighthawk populationsmore difficult. If methods are developed for more accuratecensusing of nighthawks, it may become apparent that

nighthawk populations are diminishing even faster than cur-rently recognized.

Changes in Nest BiologyThe Common Nighthawk breeds across much of NorthAmerica and winters, after a long fall migration, in SouthAmerica. In natural areas, Common Nighthawks make theirnests on open patches of ground, usually devoid of vegeta-tion and often right on sand, gravel, or scattered debris; eventhough the nests are so exposed, the adults are surprisinglycryptic on the ground. Nighthawks lay two eggs, placed di-rectly on the ground, often without even so much as a de-pression beneath them.

In the late 1800s, nighthawks were found nesting onrooftops in cities. The first reports, coming out of Philadel-phia in 1869, are mentioned by William P. Turnbull in his

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Birds of East Pennsylvania and New Jersey. In subsequent years,a large portion of the eastern population abandoned traditionalnest sites for those in urban areas. This shift in nest site selec-tion is thought to be a result of natural area reduction byhuman development and the reforestation of areas previouslycleared by agriculture and logging.

Another factor that contributed to the urbanization ofnighthawks was the construction of flat-roofed buildings withgravel or slag rooftops. These rooftops were ideal fornighthawks, but they have been phased out gradually over thepast half-century. Coverage earlier this year in Birding magazine(Paul Hess, “Nighthawks in Decline,” March/April 2013, pp.26–27; Lukas Musher, “Reversing Common Nighthawk Pop-ulation Declines,” May/June 2013, pp. 30–37) provides a thor-

ough look at how changes in urban roofing may have con-tributed to nighthawk population declines.

PhiladelphiaWhen nighthawks first began living in cities, almost every flatrooftop was covered with gravel. Although I can find no cur-rent statistics about roof types, Ray Nocella, a third-generationPhiladelphia roofer, tells me that only 2%–3% of Philadelphia’sroofs remained topped with gravel in 2008. In a conversationwith Nocella, who has spoken about his expertise in Philadel-phia rooftops to the Preservation Alliance for Greater Philadel-phia, I learned that the same basic story of slag roofs is broadlyapplicable elsewhere in the East.

From the early 1900s until about 1950, Nocella’s father and

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Although many bird species have colonized big cities relatively recently, the Common Nighthawk discoveredthe urban niche long ago. Ornithologist William P. Turnbull, writing in the mid-1800s, described thenighthawk’s use of Philadelphia rooftops for nesting. Center City, Philadelphia. Photo by © Justin Wolfe.

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grandfather installed almost exclusively slag roofs inPhiladelphia. But by the time Nocella began roofing in the1960s and 1970s, very few slag roofs were being installed.He recalls doing a few in his early days, but not many, andnone since then. In fact, his experience with slag roofs wasmostly in undoing what his father and grandfather had donebefore him. The extant slag roofs are mostly located in theless-affluent areas of Philadelphia where decrepit buildingshave remained unimproved for the past 50 years. As oldrooftops have been replaced by those constructed of newmaterials, both the nesting opportunities and the popula-tion of nighthawks in Philadelphia have dwindled.

The Pennsylvania Breeding Bird Atlas divides the area ofPhiladelphia into 28 blocks. Of those blocks, 16 reportednighthawks in the first atlas (1984–1989). By the secondatlas (2004–2008), only six Philadelphia blocks reported thepresence of nighthawks.

Other Possible Reasons for Population DeclineRecent declines in urban nighthawk populations are mostlikely linked to the change in roof design, but other possi-ble causes include increased use of insecticides, increasedpredation by crows or other aerial threats, and unknownfactors that may be influencing nighthawks in their SouthAmerican winter range.

Vector control programs in many North American cities,especially those aimed at reducing mosquitoes because ofWest Nile Virus, commonly use insecticides dispersed eitherterrestrially or from aerial platforms. The overall effect ofthese programs on flying insect populations, which are thefood source for nighthawks, is largely unstudied.

Another factor, discussed in greater detail in Musher’sBirding article, is crows. American Crows and Fish Crowsshare large portions of their ranges with nighthawks and arehighly effective egg predators. The urbanization of the Amer-

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ican Crow has been under way for decades now, and FishCrows have shown recent increases in some urban areas.Demonstrating an actual link between crow predation andnighthawk declines has proved elusive, however.

Population Restoration EffortsUrban nighthawks may well benefit from the creation of arti-ficial “nest patches,” gravel-filled frames similar to a sandboxthat can be placed on flat roofs to replicate nighthawk nestinghabitat. Nest patches have been used with success by VincentMarzilli, who reported nighthawks nesting on such patches inMaine during the 1980s. Project Nighthawk, an initiative withconnections to New Hampshire Audubon, has funded the con-struction and implementation of a number of these “Marzilli

patches.” The implementation work is ongoing. ProjectNighthawk has also produced the Gravel Nest Patch Handbook,available online <tinyurl.com/Project-Nighthawk>, which de-tails plans for the creation of artificial nest patches.

A key to success will be the placement of nest patches. Theyshould be placed on rooftops in areas where nighthawks al-ready are nesting. The hope is that juveniles, fledged fromrooftop nests, will return the next spring and use their nataland/or nearby nest patches.

The map on page 46 takes into account a number of cur-rently recognized factors to determine the optimal location toinstall nighthawk patches in Philadelphia. The square grid isbased on the system of “blocks” from the Pennsylvania BreedingBird Atlas. The area selected for habitat restoration, shown in

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It is easy to dismiss as birdless such settings as this one. But that would be a mistake. And it prompts a ques-tion: Do we birders have the will, going forward, to take the initiative to protect the nighthawk populationsthat are so evocative of summer nights in the city? Chinatown, Philadelphia. Photo by © Justin Wolfe.

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orange, is located in southeastern Philadel-phia, a residential area made up of mostlythree- and four-story row houses, many ofwhich have flat roofs (it includes the areawhere I lived when calling nighthawks firstpiqued my interest in the species). This area re-ported the strongest presence of nighthawks in thesecond Pennsylvania Breeding Bird Atlas (presence ofnighthawks indicated in blue), and it represents the largest gapin Philadelphia between areas where the city’s Vector Con-trol program uses insecticides (sprayed areas shown ingreen). Nighthawks also were present in this area duringfieldwork for the first Pennsylvania atlas, 20 years earlier.(Blocks that had nighthawks in the first atlas, but not the second,are indicated in red.) It seems safe to say that this region of the cityis a holdout for nighthawk populations, and we hope that it can serveas a source population for nighthawk increases in the region.

Why does any of this matter? Why is it important to restore urbanpopulations of Common Nighthawks?

A practical reason is the ecological service nighthawks and otheraerial insectivores (including bats) provide by helping to control in-sect populations in cities. Predation by nighthawks and other aerialinsectivores presents a safe and appealing alternative to sprayingwith chemicals.

A larger reason is the contribution of the Common Nighthawk toregional and even hemispheric biodiversity. I have focused here onthe particular matter of nighthawks on theirbreeding grounds in Philadelphia, but pop-ulations are broadly declining. We all con-nect to species in ways that are personal andlocal, but it is essential to think globallyabout birds and their habitats.

Global biodiversity issues are of para-mount importance, but we’ll end on ahuman note. Nighthawks are wonderfullynostalgic; people feel a strong connectionwith this beautiful bird and the long sum-mer evenings they evoke. Developmentcontinues to eliminate remaining naturalareas across the continent, especially inurban districts. Let’s not alienate a useful,charismatic species that has adapted so wellto life in human-modified landscapes.

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What have been your experiences with the ABA 2013 Bird of theYear? Share your thoughts and stories online: aba.org/birdingPhoto by © Judd Patterson.

Preserving Common Nighthawk Populations inPhiladelphia. Red blocks had Common Nighthawks inthe first Pennsylvania Breeding Bird Atlas, but not thesecond. Blue blocks had Common Nighthawks in boththe first and second atlases. Green areas have been re-cently sprayed for insects. The orange region has beenselected for nighthawk habitat restoration. See text foradditional details. Map by © Kei Sochi.

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