When the

Too-Early Bird Sings

In spring songbirds greet the rising

and setting sun with a cacophony

of chirps meant to entice mates and

claim territory. But artificial light

has made the night sky brighter and

disrupted the seasonal rhythms

of birds that use day length as a cue

to sing. Of six songbird species

that scientists studied in Germany,

four started singing earlier in the year

because of night lighting. The long-

term effects of light pollution on

birds’ ecosystems, and their survival,

remain unclear.

LIKELIHOOD OF SINGING

At sites with artificial light

At sites without artificial light

Gray areas indicate days with no data.

At sites exposed to

artificial light, robins

sing at dawn about

18 days earlier.

WINTER

SPRING

100%

50%

0%

100%

50%

0%

DAWN

DUSK

ROBIN

Hormones stimulated by artificial lighting at

night may lead songbirds such as robins

to begin their mating calls earlier in the year.

BLACKBIRD

During winter, blackbirds (and robins) may

spend more time foraging in well-lit urban

areas where they find warmth and more food.

BLUE TIT

Both tit species sing earliest in the year, at both

dawn and dusk. For the blue tit, artificial light

has a significant impact only at dusk.

GREAT TIT

Scientists don’t know if longer mating seasons

caused by artificial light will increase nesting

success or exhaust birds like the great tit.

When the Too-Early Bird Sings

In spring songbirds greet the rising and setting sun with a cacophony

of chirps meant to entice mates and claim territory. But artificial light

has made the night sky brighter and disrupted the seasonal rhythms

of birds that use day length as a cue to sing. Of six songbird species

that scientists studied in Germany, four started singing earlier in the year

because of night lighting. The long-term effects of light pollution on

birds’ ecosystems, and their survival, remain unclear.

BLACKBIRD

LIKELIHOOD OF SINGING

During winter, blackbirds (and robins) may spend

more time foraging in well-lit urban areas where

they find warmth and more food.

At sites with artificial light

At sites without artificial light

At sites exposed to

artificial light, robins sing

at dawn about 18 days earlier.

100%

50%

BLUE TIT

Both tit species sing earliest in the year, at both

dawn and dusk. For the blue tit, artificial light has

a significant impact only at dusk.

0%

100%

50%

0%

DAWN

DUSK

SPRING

WINTER

ROBIN

Gray areas indicate days

with no data.

Hormones stimulated

by artificial lighting at

night may lead songbirds

such as robins to begin

their mating calls earlier

in the year.

GREAT TIT

Scientists don’t know if longer mating seasons

caused by artificial light will increase nesting

success or exhaust birds like the great tit.