WILDLIFE OASES IN A CONCRETE JUNGLEyorfrcity's green roofs attract swrprisingly large numbers

RacnBl NuwrnA resourceful researcher discouers that Neut

of migratory birds and their insect Prey Bv

New York City's congested avenues

and imposing skyscrapers hardly seem

like suitable wildlife habitat, save per-

haps for the most hardy pigeon or rat'

But each year a teeming diversity ofmigrating birds pass through this

urban iungle. While most of those

feathered visitors are drawn to large

expanses of green such as Central

Park, Prospect Park and famaica BaY,

others congregate in whatever small

pockets of habitat theY can find-avacant lot or a bushY median striP-where they feed and rest before con-

tinuing on their waY. Now, a growing

number of green roofs in the city are

adding to those avian refuges, provid-ing safe havens high above the honk-

ing cabs and frenetic crowds.

FRAMED BY THE MANHATTAN SKYLINE, rB$earcher CIustin Partridge collects

spgciillens 0n the cultivated r00f 0f a building In Brooklyn, one of his study sites

tirat migratory birds have heen uslnq as resting and feeding stops during rnigration.

runoff, reduce urban heat, Provideinsulation for buildings and incorpo-

rate nature into cities. Although in

the United States the green-rooftrend only caught on relativelY

recendy, it is quickly gaining traction.

According to a survey conducted bY

the organizatton Green Roofs for

Healthy Cities, the U.S. green-roofindustry grew by 24 Percent in20LZalone. During that year, ProPertyowners in New York CitY installed

nearly 400,000 square feet of green

roofs on 93 buildings."In the past five years or so, build-

ing owners, architects and city plan-

ners started requesting and even

demanding this kind of addition to

their buildings," says Lauren Mandel,

project manager and rooftop agricul-

ture specialist for Roofmeadow, a

green-roof design and engineering

firm based in PhiladelPhia.

"Green roofs are a win-win all

around," says Dustin Partridge, a doc-

toral candidate in biology at Fordham

University who has been studying such

roofs in New York since 2009. "They

are ffuly sustainable," Partridge says.

Green roofs-defined as any roofcovered with soil or other growingmedium and veget2lisn-12[e many

forms. Some are comPosed of mostlY

small succulents that require littlemaintenance; others are designer gar-

dens with deeper soil and a greater

diversity of plant life. Some even

serve as small urban farms.

For years, residents in Switzerland,

Germany and other EuroPean coun-

tries have valued green roofs for their

ability to mitigate storm-water

I 12 I NATIONAL WILDLIFE

tNsEcr DIvERslrv is six times greater on lrlew York's Ereen roofs than sn tfue city,straditional roofs, prouiding fosd for sprin$ migrants such as the maqnolia warbler-

Partridge values the economic andaesthetic incentives for building greenroofs, but his true passion is wildlife.Green-roof supporters assume that thesites promote biodiversity, but hewanted to quantify just how signifi-cant a role they play for atrractingwinged and feathered creatures. A fewstudies in Europe menrion bird pres-ence on green roofs, but research onhow the animals :lrcilize such roofs inNorth America is almost nonexistent.

Partridge's study took place on l0green roofs scattered throughout NewYork's boroughs, six managed by thecity and the other four privatelyowned. For every private green-roofstudy site, he also gained access to anearby traditional roof--which typi-cally is covered in tar or rock ballast oris painted silver-so he could deter-mine how the two compared.

About 130 species of neotropicalmigrant pass through the city eachspring and fall while traveling alongthe Atlantic flyway-one of NorthAmerica's largest bird-migrationroutes. In the city's 840-acre CentralPark, birders can spot more than 200species annually. Those countsinclude other rypes of birds in addi-tion to the migrants.

To see how the birds do or don'ttake advantage of green roofs, Par-tridge visited each privately ownedbuilding in the study once a week

I 14 I NATTONAL WtLDLtFE

fun experience," he says.

Partridge has identified abouthalf of the 20,000 arrhropods he col-lected, and his study indicares thatinsect diversity may be about sixtimes greater on green roofs than ontraditional roofs. Those insects, hepoints out, are valuable food sourcesfor birds.

Though difficult for some NewYorkers to believe, pigeons seem to beno more common on green roofs thanon other roofs. Additionally, Partridgedid not collect a single cockroach on agreen roof, and he never saw a rat.

Though the types of birds that visitthe roofs do not differ by location, theresearcher found that each roofsarrhropod community is different.Partridge thinks this might be due tothe diversity of paths that smallarthropods take. Some, such as largebeetles and bees, can fly up to a greenroof, while others arrive in the soil oron plants. Still others, like spiders,can hitch a ride by getting caught upin the wind. "For bugs, green roofsare essentially flying islands," he says."Some get lucky and land wherethey're able to survive and persist."

Partridge points out that his studydoes not assess the quality of greenroofs as habitat for birds, though otherresearchers have demonstrated thattiny parks and other small urbanstopover sites provide valuable loca-tions for birds to rebuild their fat andmuscle tissue during migration breaks.But his resuks do indicate rhar biodi-versity on green roofs is significant.

This biodiversity likely will increasein the years to come. As more andmore green roofs sprout up, Partridgepoints out, they will form a patchworkof bird habitat that is only divided bythin canyons of the sffeet below. "Aer-ial images of some cities in Europeshow green roofs all over the place," hesays. "In the future, that could be some-thing that happens in New York."

Neut Yorftcuriter RACHEL NUWER

uisited green roofs cuith Dustin Part-ridge to reportfor this article.

from mid-April through the begin-ning of August in 2011 and 2012. Hespent about two hours in the earlymorning on the roofs recording thespecies, and he visited the sites inpairs-one traditional, one green. Inboth and on the public buildings inhis study, he set up autonomous unitsthat recorded bird vocalizations, start-ing half an hour before sunrise andcontinuing until just after sunset. Healso kept records and took specimensof the arthropods he found.

Partridge continues to analyze hisdata, but his results so far are telling.Twenty-six of the 37 bird speciesobserved in the study turned up onlyon green roofs. The researcher com-monly spotted or heard flycatchers,magnolia warblers and peregrine fal-cons. Some surprise visitors alsoappeared, including woodcocks andhummingbirds. "seeing a humming-bird nine stories up in the Bronx is a