Sky & Telescope - January 2024 - 37

active during the daytime but migrate at night. These birds
may die when they collide with lit structures, especially glass
windows as day breaks.
Research with weather radar, which is sensitive enough
to detect individual birds, has shown that birds are indeed
attracted to lighted areas from even kilometer-scale distances
and that anthropogenic light influences the distribution of
birds across the landscape during their migration. In these
cases, the birds aren't choosing their stopover habitats because
the locations are the highest quality but because they're lured
by lights. As a consequence, migrating birds are exposed to the
excess dangers associated with urban conditions.
A major consequence of animals changing their movement
patterns in response to lights can be the fragmentation of
landscapes into smaller pieces. Lights themselves can create
a barrier to movement, acting alone or in concert with other
features such as roads. In aquatic environments, for example,
bridge lights can prevent young salmon from migrating downstream,
even without a physical barrier in their way. Young
salmon naturally move during darkness, and when under
lights they will hunker down like it's daytime. Some species of
bats commuting from their roosts will avoid lighted areas and
consequently must fly around them. Researchers think these
behaviors are attempts to avoid being seen by predators.
In other instances, nocturnally active species avoid lights
to reduce contact with humans. Several studies show that
mountain lions keep to the darkest parts of the landscapes
they are in and will avoid areas with lights. For this reason,
controlling lights and creating dark pathways of approach is
important for the design of wildlife-crossing structures for
roadways.
Physiology: A Matter of
Timing
Artificial light also serves as a signal
that affects the timing and rhythms of
organisms, resulting in a wide number of
physiological and behavioral changes. It is here
where research on human health and on other
species overlaps.
Nearly every organism that lives on Earth's surface (as
opposed to in the abyss of the ocean or deep in caves) has
intrinsic daily rhythms that are kept synchronized by light.
Exposure to light at night, even at relatively low levels, can
upset those rhythms. Researchers have extensively investigated
this for humans, often using mice as a model organism.
Exposure to light at night has been associated with a whole
suite of diseases, most notably breast, prostate, and several
other cancers, as well as diabetes, obesity, sleep disorders,
depression, and stress.
For breast cancer, researchers think nighttime light exposure
prompts disease by suppressing the production of the
hormone melatonin. Melatonin serves many roles in regulating
systems in the body, suppresses cancerous growth, and is
produced only in the dark. Large studies consistently connect
outdoor nighttime lighting levels measured by satellites with
SOYBEANS This drone photo of a soybean field in Fairview, Alabama,
shows how the crop's behavior changes when exposed to artificial light
at night. Under normal conditions, the soybeans mature, die, and dry out
(brown areas), after which they're harvested. But near the streetlight, the
plants stay green. Note the long brown strip inside the green area: This is
where the pole's shadow blocked light from reaching the plants, enabling
them to mature naturally.
sk yand tele scope .o r g * JANUARY 2024 37
HONEYCOMB: ALEKSA__CH / SHUTTERSTOCK.COM; BEE: BELENOVA_
ART / SHUTTERSTOCK.COM; SOYBEANS: BEN TANKERSLEY / ALABAMA
COOPERATIVE EXTENSION SYSTEM
http://www.SHUTTERSTOCK.COM http://www.SHUTTERSTOCK.COM http://skyandtelescope.org
Sky & Telescope - January 2024

Table of Contents for the Digital Edition of Sky & Telescope - January 2024
