Science - USA (2022-04-22)

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scales. On weather radar, multispecies rivers
of passing birds can be filtered out from rain-
clouds, allowing their large scale movements
to be forecast like weather. (Meteorologists
face the same problem—telling apart birds
and storm systems—in reverse.) But it took
the advent of cloud computing and modern
machine learning to crunch through enough
data to make BirdCast work.
In 2017, the team did a small-scale test
of its methods at the Tribute in Light, prov-
ing that a single radar station—even one
on Long Island, relatively far from the art
installation—could quantify how birds move
on both large and fine-grained scales. A year
later, van Doren and Horton let machine
learning models loose on 23 years of conti-
nental U.S. weather data. They found peak
migration nights regularly involve half a
billion birds aloft over the sleeping United
States. Given a weather forecast of upcoming
temperatures and winds, their model could
predict variations in when and where the

birds would fly with 62% accuracy 1 week

ahead of time, rising to 75% 1 day in advance.

Since then, checking tomorrow’s Bird-

Cast has become “common vernacular” for

everyone from hobbyists planning birding

trips to scientists, says Emily Cohen, a mi-

gration ecologist at the University of Mary-

land Center for Environmental Science.

“This real-time forecasting of animal move-

ments is really unprecedented and super-

exciting.” The Cornell team is working to

leverage those predictions to help with

the siting of future wind turbines, to fore-

cast spikes in disease transmission from

wild birds to farmed poultry, and to antici-

pate elevated risks of birds smashing into

planes, which has bedeviled aviators since

the Wright brothers.

At the same time, other teams are using

GPS trackers mounted on individual ani-

mals to give a bird’s-eye view of the same big

patterns. One study published this month

in the Journal of Applied Ecology mapped

migration paths in North Africa and Eu-

rope, identifying areas where new turbines

or power lines would cause collisions.

The birdcasts also reveal where and when

migratory flows collide with concentrations

of light. In 2019, a study led by Horton ranked

the U.S. cities where birds face the greatest

collision risk from lights. Chicago, Houston,

and Dallas came in on top, as the most light-

polluted areas along heavy migration routes

(see graphic, p. 344). That information soon

percolated to local conservation groups.

Bird advocates have long organized vol-

untary “Lights Out” campaigns during mi-

gration season in a few cities, starting as far

back as the 1990s in Toronto, and spread-

ing to at least 44 U.S. cities today. Bird-

Cast data allow conservationists to amplify

this message on the exact nights millions

of birds are likely to cross an area, using

tweets, newsletters, and targeted emails to

everyone from bird rehabbers to downtown

building managers. “It’s wonderful policy

influenced by data,” Marra says.

Seeing the ignominious placement of

Texan cities on Horton’s list—and a Lights

Out program already in place in Chicago

since the late ’90s—the BirdCast group de-

cided to focus its own resources in Texas,

joining a smaller campaign that had begun

after 400 birds dashed themselves against

a single Galveston skyscraper one night

in 2017. In 2020, 14 major buildings par-

ticipated across the state; in 2021, it was

more than 100. Most of the iconic skyline

buildings in Dallas and Houston turned

off nonessential lights last spring and fall

for several peak migration weeks during

which at least 50% of migrating birds were

expected to pass over. Other buildings, for

example in downtown Fort Worth, kept their

lights off for months to cover the full migra-

tory season. Texas homeowners can sign up

for BirdCast alerts that provide narrower

night-by-night warnings.

The ability to quantify the risks with radar

data has also encouraged advocates to push CREDITS: (PHOTO LLOYD CLAYTON/CORNELL LAB OF ORNITHOLOGY; (GRAPHIC C. BICKEL/

SCIENCE

; (DATA B.M. VAN DOREN AND K.G. HORTON, YEARS OF MIGRATION FORECAST

MAP; BIRDCAST MIGRATION FORECAST MAP, 8 SEPTEMBER 2021 20:00 EST; CORNELL LAB OF ORNITHOLOGY; COLORADO STATE UNIVERSITY; UNIVERSITY OF OXFORD

Houston

Dallas

Chicago

N e w Yo r k

City

Low High

Migration intensity

548

million

birds predicted

8 September 2021

In fall 2020, the city of Dallas turned out lights (left) to spare migratory birds, somewhat dimming the city’s typically bright nightscape (right).

Night moves
On peak nights during migration seasons, some half a billion birds fly over the sleeping United States. Based
on weather and flight paths, models can forecast where their densities, and peril from city lights, will be highest.

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