Nocturnal migratory birds follow rhythm of the moon

Researchers have investigated how the moon affects the red-necked nightjar
Photo Credit: Carlos Carmacho

Scientific Frontline: Extended "At a Glance" Summary: Lunar-Driven Life Cycles in Nocturnal Migratory Birds

The Core Concept: The complete annual life cycle of the red-necked nightjar—including feeding, migration, and breeding—is strictly synchronized with the 29-day lunar cycle due to its reliance on moonlight for energy acquisition.

Key Distinction/Mechanism: Unlike nocturnal animals equipped with echolocation, nightjars cannot hunt effectively in total darkness; they forage intensely during full moons to build energy reserves and enter a temporary, energy-saving hibernation state by lowering their body temperature during dark nights.

Major Frameworks/Components:

• Multi-Sensor Telemetry: Utilizing advanced data loggers to continuously measure flight activity, body temperature, and behavioral patterns year-round.
• Lunar-Synchronized Energy Balancing: A physiological strategy involving fasting and torpor (lowering body temperature) during dark phases, juxtaposed with aggressive caloric intake during moonlit nights.
• Phenological Alignment: The precise timing of critical life events, such as initiating spring migrations approximately two weeks post-full moon and timing egg-hatching to coincide with peak moonlight and nocturnal insect availability.

Branch of Science: Ornithology, Behavioral Ecology, Chronobiology, Conservation Biology

Future Application: These findings provide a critical scientific baseline for assessing the environmental impact of artificial light at night (ALAN) and guide the implementation of protective conservation policies for vulnerable nocturnal species.

Why It Matters: The research highlights the fragile energy margins of nocturnal foragers, underscoring that increasing global light pollution could critically disrupt the delicate energy balances and reproductive success of species dependent on natural celestial light rhythms.

The team tracked the birds using advanced multi-sensor data loggers
Photo Credit: Carlos Carmacho

Moonlight determines when the red-necked nightjar (Caprimulgus ruficollis) feeds, migrates, and raises its young. A groundbreaking long-term study from Lund University shows how the migratory bird’s entire annual cycle follows the moon’s rhythm.

“. . . the lovely, melancholy moonlight, which makes the birds dream in the trees . . .”

The French poet Paul Verlaine was seemingly wrong in his famous poem "Clair de Lune." Moonlight does not make the birds dream up in the treetops—quite the opposite.

In a new study, researchers investigated how the moon affects the red-necked nightjar—a bird with a tapping “kjotok-kjotok” call that breeds in southern Europe and spends winters in West Africa. The research shows that the nightjar relies heavily on the moon’s light. When the moon is full, the bird can hunt insects for much of the night. When the moon is dark, the bird is instead forced to rely on brief hunting opportunities at dusk and dawn.

“Unlike bats, the nightjar lacks the ability to navigate effectively in total darkness. This is an animal that lives with small margins. Without moonlight, the energy balance simply doesn’t add up,” says Anders Hedenström, a professor of biology at Lund University.

The study is based on over 10 years of fieldwork in Doñana National Park in Spain, where researchers tracked the birds using advanced multi-sensor data loggers developed in Lund. The technology made it possible to measure flight activity, body temperature, and behavior around the clock, all year round—and to link the changes directly to the phases of the moon, which follow a 29-day cycle.

The team tracked the birds using advanced multi-sensor data loggers (photo by Carlos Carmacho).

When the light disappears, the birds are forced to slow down. They sit still for long periods and conserve energy by lowering their body temperature, a temporary hibernation strategy that is otherwise uncommon in birds.

“The most surprising thing was how clearly the dark nights trigger this energy-saving strategy. They shut down regularly every month,” says Gabriel Norevik, a biology researcher at Lund University.

However, when the full moon returns, conditions change quickly. Food intake increases, energy reserves are built up, and the birds can begin to prepare for the next demanding phase of their lives. The spring migration from Africa, for example, only begins when the energy balance allows it—usually around two weeks after the full moon.

Light Pollution a Threat to the Life Cycle of Animals

The moon’s rhythm also governs breeding. Eggs are laid so that the chicks hatch when the supply of nocturnal insects is at its peak, maximizing their chances of survival during the first critical weeks.

The results show how vulnerable nocturnal animals are to changes in the light environment, especially in a world of increasing light pollution and climate change. Even small changes in light levels can have major consequences for species already living close to their energy limits.

“The next step is to understand how artificial light affects these systems. If we alter the nighttime light, we risk disrupting their entire life cycle. This knowledge is vital when it comes to implementing conservation measures,” concludes Anders Hedenström.

Published in journal: Science Advances

Title: Moonlight drives the energy balance and annual cycle of a nocturnal forager

Authors: Carlos Camacho, Gabriel Norevik, Pedro Sáez-Gómez, Paula Hidalgo-Rodríguez, Julio Rabadán-González, Susanne Åkesson, and Anders Hedenström

Source/Credit: Lund University | Johan Joelsson

Reference Number: zoo050226_01

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