SCIENCE science.org 22 APRIL 2022 • VOL 376 ISSUE 6591 343for deeper policy commitments. Newsworthy
mass mortality events add to the pressure,
such as on 14 September 2021, when heavy
migration combined with stormy weather
and low cloud cover in New York City led
to what Parkins calls a daylong “collision
massacre.” She says that “to get legislation
passed, you have to have the science.”
In December 2021, after hearing testimony
from Farnsworth and others, the New York
City Council voted to require city-owned
buildings to turn off lights on peak migra-
tion nights, joining several other U.S. cities
like Austin, Texas, which passed a similar
bill earlier last fall. New York state legisla-
tors have also introduced a more aggressive
bill that would compel private structures,
including residences statewide,
to dim or turn off most non-
essential lights by 11 p.m. all year. In
Illinois, a law passed in summer 2021
requires new state-owned buildings to
use bird-safe glass and dimmer, down-
cast lights shown to reduce collisions;
another proposed state bill would ban
nonessential lighting during migra-
tion season for new buildings near
ecological preserves.THESE MEASURES are incremental,
and researchers are eager to learn
whether they will help even in the
middle of light-polluted urban en-
vironments. In one study, published
in summer 2021 in the Proceedings
of the National Academy of Sci-
ences, van Doren and colleagues
drew on a unique data set: bird col-
lision records compiled by volun-
teers from Chicago’s Field Museum
during 40 years of morning walks
around the perimeter of the city’s
McCormick convention center, on
the Lake Michigan waterfront.
From 2000 to 2020, almost 12,000
sparrows, warblers, thrushes, and
other birds died at the conventioncenter. The worst single nights left more
than 100 bodies behind. Wind conditions
and the intensity of migrating birds spotted
in archival weather radar seemed to predict
how many birds hit the convention center
each night, the team found.
But another key factor was how many of
the convention center’s windows had been
illuminated. Each individual bright window
left more dead birds for volunteers to find the
next day. The correlation suggests halving the
number of lit window bays would halve the
number of bird strikes, the team estimated,
saving thousands of birds at this one three-
story building. “It really does seem that each
window makes a difference,” van Doren says.
Despite the study and the negative pressthat resulted, the convention center hasn’t
updated its lighting policy during migra-
tion season, says Annette Prince, part of a
volunteer group that tracks bird collisions
in downtown Chicago. “It’s disappointing,
because they do have drapes.”
Cynthia McCafferty, a spokesperson for
the convention center, says the customers
who use the building for events dictate the
hours the lights stay on. “We have to serve
our clients.” She adds that closing drapes in
the evening would require workers to bring
in heavy equipment.
Harder data on the efficacy of Lights Out
campaigns are still forthcoming. The Bird-
Cast group, for example, is working with
volunteers in Dallas and other Texan sites to
build a bigger data set of collisions, as
tracked by body counts in the morn-
ing. Between 100,000 and 200,000
birds perish in Dallas alone each
year, Farnsworth says. Assuming van
Doren’s findings scale up, their hope
is that turning down the city’s glow by
half could halve that casualty count.
Horton is developing sharper-
than-ever migratory forecasts by
incorporating information beyond
atmospheric conditions, including
an area’s vegetation and levels of
light pollution. He’s also identify-
ing public communication strategies
to translate them into action. Light
pollution harming wildlife is still an
unfamiliar concept to many, he says.
“Having your porch light on doesn’t
sound the same as pouring paint
down the sewer.”
But that means it’s also not politi-
cally polarized, unlike many environ-
mental topics. “I don’t think there’s
many people out there who are like, ‘I
want to keep my lights on to kill color-
ful songbirds,’” Horton says. jJoshua Sokol is a science journalist in
CREDITS: (PHOTO LLOYD CLAYTON/CORNELL LAB OF ORNITHOLOGY; (GRAPHIC K. FRANKLIN/ Raleigh, North Carolina.
SCIENCE
; (DATA K. HORTON, A. FARNSWORTH
ET AL
.,
FRONTIERS IN ECOLOGY AND THE ENVIRONMENT, 17, 4, (2019 LowHighSpring FallRelative exposure of birds to light5 15 25 35 45Dark Light radiance BrightChicago
DallasNew York CityHoustonChicagoHoustonN e w Yo r k C i t yDallasFlight risks
By using satellite maps to quantify light at night and radar to estimate
the numbers of migratory birds streaming across the night sky,
scientists have ranked the cities where birds face the most danger
from light pollution. Chicago tops the list in both spring and fall.