Scientific American - USA (2022-03)

84 Scientific American, March 2022

GRAPHIC SCIENCE

Text and Graphic by Katie Peek

Mexico City

Monterrey, N.L.

Corpus

Christi, Tex.

Houston

Dallas

Atlanta

Nashville

St. Louis

Washington

New York

Chicago

Toronto

Minneapolis

Montreal

Quebec City

Thunder

Bay, Ont.

Winnipeg,

Man.

Monarch

wintering

grounds^20 °

60 °

50 °

40 °

30 °

Edmonton,

Alta.

Calgary, Alta.

March April May June July

1–15 16–31 1–15 16–30 1–15 16–31 1–15 16–30 1–15 16–31

Latitude

2,266 4,482 5,229 4 ,1 6 4 4,031 9,218 7, 7 7 6 5,524 9,050

11,893 observations

2,266 4,482 5,229 4 ,1 6 4 4,031 9,218 7, 7 7 6 5,524 9,050

11,893 observations

The Great

Monarch

Odyssey

Citizen science data

reveal where and when

the famously itinerant

butterflies travel

It’s spring, and monarchs are on the

move. Every year the butterflies leave

their dense winter clusters near Mexi-

co City and head for northern latitudes.

It will take four months and three gen-

erations to get there. Once they arrive,

the butterflies will get busy boosting

their company enough to survive next

year’s winter. It’s a Si syphean task—

eastern monarch numbers have dropped

80 percent in the past 20 years because

of habitat degradation (in clud ing few-

er flowers)—throughout their range,

says Iman Momeni-De hag hi, a biologist

at Carleton University in Ottawa. Enter

citizen scientists, who have been build-

ing databases such as Journey North,

which Momeni-Dehaghi re cent ly used

to identify where the overwintering

generation hatches. The data could help

re search ers devise more targeted in ter-

ventions for a species

in rapid decline.

Area Included
Monarchs from wintering
grounds in Mexico ( orange star )
spread through North America east
of the Rockies. Florida is excluded because
its monarchs over winter
there rather than
in Mexico.

15 °

30 °

45 °

60 °

15°

30°

45 °

60°

First Generation

The spring eggs

gestate for a month

or so. By late April

first-generation

monarchs emerge

and begin to fly

north, laying eggs

as they go.

The Old Guard

In March the mon-

archs that wintered in

Mexico move north. In

northern Mexico and

the southern U.S., they

lay the eggs that will

be the first generation

of the next life cycle.

Second Generation

In late May and early

June the second gen er a-

tion hatches. The South

will soon be too hot for

monarchs, so those

born there move north.

Their objective:

make more butterflies.

Third and Fourth Generations

In late summer the last generations

emerge in the northern part of the

monarch range. These are the butter-

flies that will make the trek south

again, starting in September. They

will spend November through March

in the mountains of Michoacán,

then begin the cycle anew.

HOW TO READ

THIS GRAPHIC

Each shape represents

sightings of eastern

monarchs—eggs,

larvae and adult

butter^ flies—logged

in the Journey North

database between

2012 and 2021 (more

than 66,000 data

points). For each shape,

width represents the

number of sightings

during that half

month, corrected by

the human population

at that latitude.

Sources:

Monarch Sightings from Journey North Citizen Science Data (

journeynorth.org

);^

Population Data from Columbia University’s Socioeconomic Data and Applications Center (S

EDAC

)